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diff --git a/libstdc++-v3/doc/html/ext/lwg-closed.html b/libstdc++-v3/doc/html/ext/lwg-closed.html deleted file mode 100644 index b01c109c744..00000000000 --- a/libstdc++-v3/doc/html/ext/lwg-closed.html +++ /dev/null @@ -1,42632 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" - "http://www.w3.org/TR/html4/strict.dtd"> -<html> -<head> -<title>C++ Standard Library Closed Issues List</title> -<style type="text/css"> - p {text-align:justify} - li {text-align:justify} - blockquote.note - { - background-color:#E0E0E0; - padding-left: 15px; - padding-right: 15px; - padding-top: 1px; - padding-bottom: 1px; - } - ins {background-color:#A0FFA0} - del {background-color:#FFA0A0} -</style> -</head> -<body> -<table> -<tr> - <td align="left">Doc. no.</td> - <td align="left">N4486</td> -</tr> -<tr> - <td align="left">Date:</td> - <td align="left">2015-05-23</td> -</tr> -<tr> - <td align="left">Project:</td> - <td align="left">Programming Language C++</td> -</tr> -<tr> - <td align="left">Reply to:</td> - <td align="left">Marshall Clow <<a href="mailto:lwgchair@gmail.com">lwgchair@gmail.com</a>></td> -</tr> -</table> -<h1>C++ Standard Library Closed Issues List (Revision R93)</h1> -<p><p>Revised 2015-05-23 at 15:05:40 UTC</p> -</p> - <p>Reference ISO/IEC IS 14882:2014(E)</p> - <p>Also see:</p> - <ul> - <li><a href="lwg-toc.html">Table of Contents</a> for all library issues.</li> - <li><a href="lwg-index.html">Index by Section</a> for all library issues.</li> - <li><a href="lwg-status.html">Index by Status</a> for all library issues.</li> - <li><a href="lwg-active.html">Library Active Issues List</a></li> - <li><a href="lwg-defects.html">Library Defect Reports List</a></li> - </ul> - - <p>This document contains only library issues which have been closed - by the Library Working Group as duplicates or not defects. That is, - issues which have a status of <a href="lwg-active.html#Dup">Dup</a> or - <a href="lwg-active.html#NAD">NAD</a>. See the <a href="lwg-active.html">Library Active Issues List</a> active issues and more - information. See the <a href="lwg-defects.html">Library Defect Reports List</a> for issues considered - defects. The introductory material in that document also applies to - this document.</p> - -<h2>Revision History</h2> -<ul> -<li>R93: 2014-05-22 2015 post-Lenexa mailing<ul> -<li><b>Summary:</b><ul> -<li>256 open issues, down by 36.</li> -<li>1770 closed issues, up by 48.</li> -<li>2026 issues total, up by 12.</li> -</ul></li> -<li><b>Details:</b><ul> -<li>Added the following 2 Ready issues: <a href="lwg-active.html#2492">2492</a>, <a href="lwg-active.html#2494">2494</a>.</li> -<li>Added the following 10 New issues: <a href="lwg-active.html#2493">2493</a>, <a href="lwg-active.html#2495">2495</a>, <a href="lwg-active.html#2496">2496</a>, <a href="lwg-active.html#2497">2497</a>, <a href="lwg-active.html#2498">2498</a>, <a href="lwg-active.html#2499">2499</a>, <a href="lwg-active.html#2500">2500</a>, <a href="lwg-active.html#2501">2501</a>, <a href="lwg-active.html#2502">2502</a>, <a href="lwg-active.html#2503">2503</a>.</li> -<li>Changed the following 2 issues to Ready (from Review): <a href="lwg-active.html#2111">2111</a>, <a href="lwg-active.html#2380">2380</a>.</li> -<li>Changed the following 20 issues to Ready (from New): <a href="lwg-active.html#2244">2244</a>, <a href="lwg-active.html#2250">2250</a>, <a href="lwg-active.html#2259">2259</a>, <a href="lwg-active.html#2336">2336</a>, <a href="lwg-active.html#2353">2353</a>, <a href="lwg-active.html#2367">2367</a>, <a href="lwg-active.html#2384">2384</a>, <a href="lwg-active.html#2385">2385</a>, <a href="lwg-active.html#2435">2435</a>, <a href="lwg-active.html#2462">2462</a>, <a href="lwg-active.html#2466">2466</a>, <a href="lwg-active.html#2473">2473</a>, <a href="lwg-active.html#2476">2476</a>, <a href="lwg-active.html#2477">2477</a>, <a href="lwg-active.html#2483">2483</a>, <a href="lwg-active.html#2484">2484</a>, <a href="lwg-active.html#2485">2485</a>, <a href="lwg-active.html#2486">2486</a>, <a href="lwg-active.html#2487">2487</a>, <a href="lwg-active.html#2489">2489</a>.</li> -<li>Changed the following 12 issues to Ready (from Open): <a href="lwg-active.html#1169">1169</a>, <a href="lwg-active.html#2072">2072</a>, <a href="lwg-active.html#2101">2101</a>, <a href="lwg-active.html#2119">2119</a>, <a href="lwg-active.html#2127">2127</a>, <a href="lwg-active.html#2133">2133</a>, <a href="lwg-active.html#2156">2156</a>, <a href="lwg-active.html#2181">2181</a>, <a href="lwg-active.html#2218">2218</a>, <a href="lwg-active.html#2219">2219</a>, <a href="lwg-active.html#2447">2447</a>, <a href="lwg-active.html#2469">2469</a>.</li> -<li>Changed the following issue to Tentatively Ready (from Open): <a href="lwg-active.html#2224">2224</a>.</li> -<li>Changed the following issue to Review (from New): <a href="lwg-active.html#2296">2296</a>.</li> -<li>Changed the following issue to Review (from Open): <a href="lwg-active.html#2328">2328</a>.</li> -<li>Changed the following 11 issues to Open (from New): <a href="lwg-active.html#2262">2262</a>, <a href="lwg-active.html#2289">2289</a>, <a href="lwg-active.html#2338">2338</a>, <a href="lwg-active.html#2348">2348</a>, <a href="lwg-active.html#2349">2349</a>, <a href="lwg-active.html#2370">2370</a>, <a href="lwg-active.html#2398">2398</a>, <a href="lwg-active.html#2402">2402</a>, <a href="lwg-active.html#2422">2422</a>, <a href="lwg-active.html#2450">2450</a>, <a href="lwg-active.html#2456">2456</a>.</li> -<li>Changed the following 8 issues to Open (from SG1): <a href="lwg-active.html#2245">2245</a>, <a href="lwg-active.html#2265">2265</a>, <a href="lwg-active.html#2276">2276</a>, <a href="lwg-active.html#2309">2309</a>, <a href="lwg-active.html#2363">2363</a>, <a href="lwg-active.html#2379">2379</a>, <a href="lwg-active.html#2426">2426</a>, <a href="lwg-active.html#2441">2441</a>.</li> -<li>Changed the following issue to LEWG (from New): <a href="lwg-active.html#2372">2372</a>.</li> -<li>Changed the following issue to EWG (from New): <a href="lwg-active.html#2432">2432</a>.</li> -<li>Changed the following issue to Deferred (from Open): <a href="lwg-active.html#2202">2202</a>.</li> -<li>Changed the following 14 issues to WP (from Ready): <a href="lwg-defects.html#2160">2160</a>, <a href="lwg-defects.html#2168">2168</a>, <a href="lwg-defects.html#2364">2364</a>, <a href="lwg-defects.html#2403">2403</a>, <a href="lwg-defects.html#2406">2406</a>, <a href="lwg-defects.html#2411">2411</a>, <a href="lwg-defects.html#2425">2425</a>, <a href="lwg-defects.html#2427">2427</a>, <a href="lwg-defects.html#2428">2428</a>, <a href="lwg-defects.html#2433">2433</a>, <a href="lwg-defects.html#2434">2434</a>, <a href="lwg-defects.html#2438">2438</a>, <a href="lwg-defects.html#2439">2439</a>, <a href="lwg-defects.html#2440">2440</a>.</li> -<li>Changed the following 18 issues to WP (from Tentatively Ready): <a href="lwg-defects.html#2059">2059</a>, <a href="lwg-defects.html#2076">2076</a>, <a href="lwg-defects.html#2239">2239</a>, <a href="lwg-defects.html#2369">2369</a>, <a href="lwg-defects.html#2378">2378</a>, <a href="lwg-defects.html#2410">2410</a>, <a href="lwg-defects.html#2415">2415</a>, <a href="lwg-defects.html#2418">2418</a>, <a href="lwg-defects.html#2437">2437</a>, <a href="lwg-defects.html#2448">2448</a>, <a href="lwg-defects.html#2454">2454</a>, <a href="lwg-defects.html#2455">2455</a>, <a href="lwg-defects.html#2458">2458</a>, <a href="lwg-defects.html#2459">2459</a>, <a href="lwg-defects.html#2463">2463</a>, <a href="lwg-defects.html#2467">2467</a>, <a href="lwg-defects.html#2470">2470</a>, <a href="lwg-defects.html#2482">2482</a>.</li> -<li>Changed the following 3 issues to WP (from New): <a href="lwg-defects.html#2420">2420</a>, <a href="lwg-defects.html#2464">2464</a>, <a href="lwg-defects.html#2488">2488</a>.</li> -<li>Changed the following issue to WP (from Open): <a href="lwg-defects.html#2063">2063</a>.</li> -<li>Changed the following 2 issues to WP (from SG1): <a href="lwg-defects.html#2407">2407</a>, <a href="lwg-defects.html#2442">2442</a>.</li> -<li>Changed the following issue to Resolved (from Review): <a href="lwg-defects.html#2228">2228</a>.</li> -<li>Changed the following 3 issues to Resolved (from Open): <a href="lwg-defects.html#1526">1526</a>, <a href="lwg-defects.html#2274">2274</a>, <a href="lwg-defects.html#2397">2397</a>.</li> -<li>Changed the following 5 issues to NAD (from New): <a href="lwg-closed.html#2079">2079</a>, <a href="lwg-closed.html#2251">2251</a>, <a href="lwg-closed.html#2351">2351</a>, <a href="lwg-closed.html#2373">2373</a>, <a href="lwg-closed.html#2386">2386</a>.</li> -<li>Changed the following issue to NAD (from Open): <a href="lwg-closed.html#2388">2388</a>.</li> -</ul></li> -</ul> -</li> -<li>R92: -2015-04-09 pre-Lenexa mailing -<ul> -<li><b>Summary:</b><ul> -<li>292 open issues, up by 33.</li> -<li>1722 closed issues, up by 0.</li> -<li>2014 issues total, up by 33.</li> -</ul></li> -<li><b>Details:</b><ul> -<li>Added the following 5 Tentatively Ready issues: <a href="lwg-active.html#2459">2459</a>, <a href="lwg-active.html#2463">2463</a>, <a href="lwg-active.html#2467">2467</a>, <a href="lwg-active.html#2470">2470</a>, <a href="lwg-active.html#2482">2482</a>.</li> -<li>Added the following 27 New issues: <a href="lwg-active.html#2460">2460</a>, <a href="lwg-active.html#2461">2461</a>, <a href="lwg-active.html#2462">2462</a>, <a href="lwg-active.html#2464">2464</a>, <a href="lwg-active.html#2465">2465</a>, <a href="lwg-active.html#2466">2466</a>, <a href="lwg-active.html#2468">2468</a>, <a href="lwg-active.html#2471">2471</a>, <a href="lwg-active.html#2472">2472</a>, <a href="lwg-active.html#2473">2473</a>, <a href="lwg-active.html#2474">2474</a>, <a href="lwg-active.html#2475">2475</a>, <a href="lwg-active.html#2476">2476</a>, <a href="lwg-active.html#2477">2477</a>, <a href="lwg-active.html#2478">2478</a>, <a href="lwg-active.html#2479">2479</a>, <a href="lwg-active.html#2480">2480</a>, <a href="lwg-active.html#2481">2481</a>, <a href="lwg-active.html#2483">2483</a>, <a href="lwg-active.html#2484">2484</a>, <a href="lwg-active.html#2485">2485</a>, <a href="lwg-active.html#2486">2486</a>, <a href="lwg-active.html#2487">2487</a>, <a href="lwg-active.html#2488">2488</a>, <a href="lwg-active.html#2489">2489</a>, <a href="lwg-active.html#2490">2490</a>, <a href="lwg-active.html#2491">2491</a>.</li> -<li>Added the following Open issue: <a href="lwg-active.html#2469">2469</a>.</li> -<li>Changed the following issue to Tentatively Ready (from Review): <a href="lwg-active.html#2378">2378</a>.</li> -<li>Changed the following 11 issues to Tentatively Ready (from New): <a href="lwg-active.html#2076">2076</a>, <a href="lwg-active.html#2239">2239</a>, <a href="lwg-active.html#2369">2369</a>, <a href="lwg-active.html#2410">2410</a>, <a href="lwg-active.html#2415">2415</a>, <a href="lwg-active.html#2418">2418</a>, <a href="lwg-active.html#2437">2437</a>, <a href="lwg-active.html#2448">2448</a>, <a href="lwg-active.html#2454">2454</a>, <a href="lwg-active.html#2455">2455</a>, <a href="lwg-active.html#2458">2458</a>.</li> -<li>Changed the following issue to Tentatively Ready (from Open): <a href="lwg-active.html#2059">2059</a>.</li> -<li>Changed the following issue to Tentatively NAD (from New): <a href="lwg-active.html#2337">2337</a>.</li> -<li>Changed the following issue to Tentatively NAD (from Open): <a href="lwg-active.html#760">760</a>.</li> -<li>Changed the following 5 issues to Open (from New): <a href="lwg-active.html#2312">2312</a>, <a href="lwg-active.html#2388">2388</a>, <a href="lwg-active.html#2393">2393</a>, <a href="lwg-active.html#2444">2444</a>, <a href="lwg-active.html#2447">2447</a>.</li> -<li>Changed the following 4 issues to LEWG (from New): <a href="lwg-active.html#2391">2391</a>, <a href="lwg-active.html#2417">2417</a>, <a href="lwg-active.html#2436">2436</a>, <a href="lwg-active.html#2451">2451</a>.</li> -<li>Changed the following issue to EWG (from Open): <a href="lwg-active.html#2089">2089</a>.</li> -<li>Changed the following issue to Core (from New): <a href="lwg-active.html#2452">2452</a>.</li> -<li>Changed the following 13 issues to SG1 (from New): <a href="lwg-active.html#2236">2236</a>, <a href="lwg-active.html#2245">2245</a>, <a href="lwg-active.html#2265">2265</a>, <a href="lwg-active.html#2276">2276</a>, <a href="lwg-active.html#2309">2309</a>, <a href="lwg-active.html#2334">2334</a>, <a href="lwg-active.html#2363">2363</a>, <a href="lwg-active.html#2379">2379</a>, <a href="lwg-active.html#2407">2407</a>, <a href="lwg-active.html#2412">2412</a>, <a href="lwg-active.html#2426">2426</a>, <a href="lwg-active.html#2442">2442</a>, <a href="lwg-active.html#2445">2445</a>.</li> -<li>Changed the following issue to SG1 (from Open): <a href="lwg-active.html#2441">2441</a>.</li> -</ul></li> -</ul> -</li> -<li>R91: -2014-11-23 post-Urbana mailing -<ul> -<li><b>Summary:</b><ul> -<li>259 open issues, up by 32.</li> -<li>1722 closed issues, down by 20.</li> -<li>1981 issues total, up by 12.</li> -</ul></li> -<li><b>Details:</b><ul> -<li>Added the following 12 New issues: <a href="lwg-active.html#2447">2447</a>, <a href="lwg-defects.html#2448">2448</a>, <a href="lwg-active.html#2449">2449</a>, <a href="lwg-active.html#2450">2450</a>, <a href="lwg-active.html#2451">2451</a>, <a href="lwg-active.html#2452">2452</a>, <a href="lwg-active.html#2453">2453</a>, <a href="lwg-defects.html#2454">2454</a>, <a href="lwg-defects.html#2455">2455</a>, <a href="lwg-active.html#2456">2456</a>, <a href="lwg-active.html#2457">2457</a>, <a href="lwg-defects.html#2458">2458</a>.</li> -<li>Changed the following 2 issues to Ready (from Review): <a href="lwg-defects.html#2160">2160</a>, <a href="lwg-defects.html#2364">2364</a>.</li> -<li>Changed the following 11 issues to Ready (from New): <a href="lwg-defects.html#2403">2403</a>, <a href="lwg-defects.html#2406">2406</a>, <a href="lwg-defects.html#2411">2411</a>, <a href="lwg-defects.html#2425">2425</a>, <a href="lwg-defects.html#2427">2427</a>, <a href="lwg-defects.html#2428">2428</a>, <a href="lwg-defects.html#2433">2433</a>, <a href="lwg-defects.html#2434">2434</a>, <a href="lwg-defects.html#2438">2438</a>, <a href="lwg-defects.html#2439">2439</a>, <a href="lwg-defects.html#2440">2440</a>.</li> -<li>Changed the following issue to Ready (from Open): <a href="lwg-defects.html#2168">2168</a>.</li> -<li>Changed the following issue to Review (from New): <a href="lwg-active.html#2424">2424</a>.</li> -<li>Changed the following 5 issues to Open (from New): <a href="lwg-active.html#2307">2307</a>, <a href="lwg-active.html#2310">2310</a>, <a href="lwg-active.html#2383">2383</a>, <a href="lwg-active.html#2414">2414</a>, <a href="lwg-active.html#2441">2441</a>.</li> -<li>Changed the following 2 issues to Open (from NAD Future): <a href="lwg-active.html#760">760</a>, <a href="lwg-active.html#1173">1173</a>.</li> -<li>Changed the following 4 issues to LEWG (from New): <a href="lwg-active.html#2419">2419</a>, <a href="lwg-active.html#2430">2430</a>, <a href="lwg-active.html#2443">2443</a>, <a href="lwg-active.html#2446">2446</a>.</li> -<li>Changed the following 48 issues to LEWG (from NAD Future): <a href="lwg-active.html#255">255</a>, <a href="lwg-active.html#423">423</a>, <a href="lwg-active.html#484">484</a>, <a href="lwg-active.html#523">523</a>, <a href="lwg-active.html#532">532</a>, <a href="lwg-active.html#708">708</a>, <a href="lwg-active.html#839">839</a>, <a href="lwg-active.html#851">851</a>, <a href="lwg-active.html#877">877</a>, <a href="lwg-active.html#933">933</a>, <a href="lwg-active.html#935">935</a>, <a href="lwg-active.html#936">936</a>, <a href="lwg-active.html#961">961</a>, <a href="lwg-active.html#1025">1025</a>, <a href="lwg-active.html#1031">1031</a>, <a href="lwg-active.html#1041">1041</a>, <a href="lwg-active.html#1052">1052</a>, <a href="lwg-active.html#1053">1053</a>, <a href="lwg-active.html#1112">1112</a>, <a href="lwg-active.html#1120">1120</a>, <a href="lwg-active.html#1121">1121</a>, <a href="lwg-active.html#1150">1150</a>, <a href="lwg-active.html#1154">1154</a>, <a href="lwg-active.html#1184">1184</a>, <a href="lwg-active.html#1188">1188</a>, <a href="lwg-active.html#1201">1201</a>, <a href="lwg-active.html#1203">1203</a>, <a href="lwg-active.html#1217">1217</a>, <a href="lwg-active.html#1235">1235</a>, <a href="lwg-active.html#1238">1238</a>, <a href="lwg-active.html#1242">1242</a>, <a href="lwg-active.html#1282">1282</a>, <a href="lwg-active.html#1289">1289</a>, <a href="lwg-active.html#1317">1317</a>, <a href="lwg-active.html#1320">1320</a>, <a href="lwg-active.html#1396">1396</a>, <a href="lwg-active.html#1406">1406</a>, <a href="lwg-active.html#1422">1422</a>, <a href="lwg-active.html#1459">1459</a>, <a href="lwg-active.html#1484">1484</a>, <a href="lwg-active.html#1488">1488</a>, <a href="lwg-active.html#1493">1493</a>, <a href="lwg-active.html#1499">1499</a>, <a href="lwg-active.html#1521">1521</a>, <a href="lwg-active.html#2040">2040</a>, <a href="lwg-active.html#2055">2055</a>, <a href="lwg-active.html#2226">2226</a>, <a href="lwg-active.html#2232">2232</a>.</li> -<li>Changed the following 2 issues to Pending NAD (from Tentatively NAD): <a href="lwg-closed.html#2302">2302</a>, <a href="lwg-closed.html#2382">2382</a>.</li> -<li>Changed the following 11 issues to WP (from Ready): <a href="lwg-defects.html#2016">2016</a>, <a href="lwg-defects.html#2170">2170</a>, <a href="lwg-defects.html#2340">2340</a>, <a href="lwg-defects.html#2354">2354</a>, <a href="lwg-defects.html#2377">2377</a>, <a href="lwg-defects.html#2396">2396</a>, <a href="lwg-defects.html#2399">2399</a>, <a href="lwg-defects.html#2400">2400</a>, <a href="lwg-defects.html#2401">2401</a>, <a href="lwg-defects.html#2404">2404</a>, <a href="lwg-defects.html#2408">2408</a>.</li> -<li>Changed the following 12 issues to WP (from Tentatively Ready): <a href="lwg-defects.html#2106">2106</a>, <a href="lwg-defects.html#2129">2129</a>, <a href="lwg-defects.html#2212">2212</a>, <a href="lwg-defects.html#2217">2217</a>, <a href="lwg-defects.html#2230">2230</a>, <a href="lwg-defects.html#2233">2233</a>, <a href="lwg-defects.html#2266">2266</a>, <a href="lwg-defects.html#2325">2325</a>, <a href="lwg-defects.html#2361">2361</a>, <a href="lwg-defects.html#2365">2365</a>, <a href="lwg-defects.html#2376">2376</a>, <a href="lwg-defects.html#2387">2387</a>.</li> -<li>Changed the following issue to Resolved (from Ready): <a href="lwg-defects.html#2319">2319</a>.</li> -<li>Changed the following issue to Resolved (from Review): <a href="lwg-defects.html#2118">2118</a>.</li> -<li>Changed the following issue to Resolved (from New): <a href="lwg-defects.html#2416">2416</a>.</li> -<li>Changed the following issue to Resolved (from Open): <a href="lwg-defects.html#2108">2108</a>.</li> -<li>Changed the following issue to NAD (from New): <a href="lwg-closed.html#2429">2429</a>.</li> -</ul></li> -</ul> -</li> -<li>R90: -2014-10-13 pre-Urbana mailing -<ul> -<li><b>Summary:</b><ul> -<li>227 open issues, up by 31.</li> -<li>1742 closed issues, up by 0.</li> -<li>1969 issues total, up by 31.</li> -</ul></li> -<li><b>Details:</b><ul> -<li>Added the following 31 New issues: <a href="lwg-defects.html#2416">2416</a>, <a href="lwg-active.html#2417">2417</a>, <a href="lwg-defects.html#2418">2418</a>, <a href="lwg-active.html#2419">2419</a>, <a href="lwg-defects.html#2420">2420</a>, <a href="lwg-active.html#2421">2421</a>, <a href="lwg-active.html#2422">2422</a>, <a href="lwg-active.html#2423">2423</a>, <a href="lwg-active.html#2424">2424</a>, <a href="lwg-defects.html#2425">2425</a>, <a href="lwg-active.html#2426">2426</a>, <a href="lwg-defects.html#2427">2427</a>, <a href="lwg-defects.html#2428">2428</a>, <a href="lwg-closed.html#2429">2429</a>, <a href="lwg-active.html#2430">2430</a>, <a href="lwg-active.html#2431">2431</a>, <a href="lwg-active.html#2432">2432</a>, <a href="lwg-defects.html#2433">2433</a>, <a href="lwg-defects.html#2434">2434</a>, <a href="lwg-active.html#2435">2435</a>, <a href="lwg-active.html#2436">2436</a>, <a href="lwg-defects.html#2437">2437</a>, <a href="lwg-defects.html#2438">2438</a>, <a href="lwg-defects.html#2439">2439</a>, <a href="lwg-defects.html#2440">2440</a>, <a href="lwg-active.html#2441">2441</a>, <a href="lwg-defects.html#2442">2442</a>, <a href="lwg-active.html#2443">2443</a>, <a href="lwg-active.html#2444">2444</a>, <a href="lwg-active.html#2445">2445</a>, <a href="lwg-active.html#2446">2446</a>.</li> -<li>No issues changed.</li> -</ul></li> -</ul> -</li> -<li>R89: -2014-07-08 post-Rapperswil mailing -<ul> -<li><b>Summary:</b><ul> -<li>196 open issues, up by 14.</li> -<li>1742 closed issues, up by 12.</li> -<li>1938 issues total, up by 26.</li> -</ul></li> -<li><b>Details:</b><ul> -<li>Added the following 6 Ready issues: <a href="lwg-defects.html#2396">2396</a>, <a href="lwg-defects.html#2399">2399</a>, <a href="lwg-defects.html#2400">2400</a>, <a href="lwg-defects.html#2401">2401</a>, <a href="lwg-defects.html#2404">2404</a>, <a href="lwg-defects.html#2408">2408</a>.</li> -<li>Added the following 15 New issues: <a href="lwg-active.html#2391">2391</a>, <a href="lwg-active.html#2392">2392</a>, <a href="lwg-active.html#2393">2393</a>, <a href="lwg-active.html#2394">2394</a>, <a href="lwg-active.html#2398">2398</a>, <a href="lwg-active.html#2402">2402</a>, <a href="lwg-defects.html#2403">2403</a>, <a href="lwg-defects.html#2406">2406</a>, <a href="lwg-defects.html#2407">2407</a>, <a href="lwg-defects.html#2410">2410</a>, <a href="lwg-defects.html#2411">2411</a>, <a href="lwg-active.html#2412">2412</a>, <a href="lwg-active.html#2413">2413</a>, <a href="lwg-active.html#2414">2414</a>, <a href="lwg-defects.html#2415">2415</a>.</li> -<li>Added the following Open issue: <a href="lwg-defects.html#2397">2397</a>.</li> -<li>Added the following 3 WP issues: <a href="lwg-defects.html#2390">2390</a>, <a href="lwg-defects.html#2395">2395</a>, <a href="lwg-defects.html#2409">2409</a>.</li> -<li>Added the following NAD issue: <a href="lwg-closed.html#2405">2405</a>.</li> -<li>Changed the following issue to Ready (from New): <a href="lwg-defects.html#2377">2377</a>.</li> -<li>Changed the following 2 issues to Ready (from Deferred): <a href="lwg-active.html#2253">2253</a>, <a href="lwg-active.html#2255">2255</a>.</li> -<li>Changed the following 2 issues to Tentatively Ready (from New): <a href="lwg-defects.html#2325">2325</a>, <a href="lwg-defects.html#2387">2387</a>.</li> -<li>Changed the following issue to Tentatively NAD (from New): <a href="lwg-closed.html#2382">2382</a>.</li> -<li>Changed the following 3 issues to Review (from New): <a href="lwg-defects.html#2364">2364</a>, <a href="lwg-defects.html#2378">2378</a>, <a href="lwg-active.html#2380">2380</a>.</li> -<li>Changed the following 2 issues to Review (from Open): <a href="lwg-defects.html#2118">2118</a>, <a href="lwg-defects.html#2160">2160</a>.</li> -<li>Changed the following 3 issues to Open (from New): <a href="lwg-defects.html#2168">2168</a>, <a href="lwg-active.html#2238">2238</a>, <a href="lwg-active.html#2273">2273</a>.</li> -<li>Changed the following 3 issues to Open (from Deferred): <a href="lwg-active.html#2254">2254</a>, <a href="lwg-active.html#2264">2264</a>, <a href="lwg-active.html#2277">2277</a>.</li> -<li>Changed the following 3 issues to WP (from New): <a href="lwg-defects.html#2371">2371</a>, <a href="lwg-defects.html#2374">2374</a>, <a href="lwg-defects.html#2389">2389</a>.</li> -<li>Changed the following 4 issues to Resolved (from Deferred): <a href="lwg-defects.html#2282">2282</a>, <a href="lwg-defects.html#2283">2283</a>, <a href="lwg-defects.html#2287">2287</a>, <a href="lwg-defects.html#2333">2333</a>.</li> -<li>Changed the following issue to NAD (from Deferred): <a href="lwg-closed.html#2305">2305</a>.</li> -</ul></li> -</ul> -</li> -<li>R88: -2014-05-24 pre-Rapperswil mailing -<ul> -<li><b>Summary:</b><ul> -<li>182 open issues, up by 29.</li> -<li>1730 closed issues, up by 0.</li> -<li>1912 issues total, up by 29.</li> -</ul></li> -<li><b>Details:</b><ul> -<li>Added the following 3 Tentatively Ready issues: <a href="lwg-defects.html#2361">2361</a>, <a href="lwg-defects.html#2365">2365</a>, <a href="lwg-defects.html#2376">2376</a>.</li> -<li>Added the following 26 New issues: <a href="lwg-active.html#2362">2362</a>, <a href="lwg-active.html#2363">2363</a>, <a href="lwg-defects.html#2364">2364</a>, <a href="lwg-active.html#2366">2366</a>, <a href="lwg-active.html#2367">2367</a>, <a href="lwg-active.html#2368">2368</a>, <a href="lwg-defects.html#2369">2369</a>, <a href="lwg-active.html#2370">2370</a>, <a href="lwg-defects.html#2371">2371</a>, <a href="lwg-active.html#2372">2372</a>, <a href="lwg-closed.html#2373">2373</a>, <a href="lwg-defects.html#2374">2374</a>, <a href="lwg-active.html#2375">2375</a>, <a href="lwg-defects.html#2377">2377</a>, <a href="lwg-defects.html#2378">2378</a>, <a href="lwg-active.html#2379">2379</a>, <a href="lwg-active.html#2380">2380</a>, <a href="lwg-active.html#2381">2381</a>, <a href="lwg-closed.html#2382">2382</a>, <a href="lwg-active.html#2383">2383</a>, <a href="lwg-active.html#2384">2384</a>, <a href="lwg-active.html#2385">2385</a>, <a href="lwg-closed.html#2386">2386</a>, <a href="lwg-defects.html#2387">2387</a>, <a href="lwg-closed.html#2388">2388</a>, <a href="lwg-defects.html#2389">2389</a>.</li> -<li>Changed the following 5 issues to Tentatively Ready (from Open): <a href="lwg-defects.html#2106">2106</a>, <a href="lwg-defects.html#2129">2129</a>, <a href="lwg-defects.html#2212">2212</a>, <a href="lwg-defects.html#2230">2230</a>, <a href="lwg-defects.html#2233">2233</a>.</li> -</ul></li> -</ul> -</li> -</ul> - -<h2>Closed Issues</h2> -<hr> -<h3><a name="2"></a>2. Auto_ptr conversions effects incorrect</h3> -<p><b>Section:</b> X [auto.ptr.conv] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nathan Myers <b>Opened:</b> 1997-12-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Paragraph 1 in "Effects", says "Calls -p->release()" where it clearly must be "Calls -p.release()". (As it is, it seems to require using -auto_ptr<>::operator-> to refer to X::release, assuming that -exists.)</p> - - -<p><b>Proposed resolution:</b></p> -<p>Change 20.10.4.3 [meta.unary.prop] paragraph 1 Effects from -"Calls p->release()" to "Calls p.release()".</p> - - -<p><b>Rationale:</b></p> -<p>Not a defect: the proposed change is already found in the standard. -[Originally classified as a defect, later reclassified.]</p> - - - - - -<hr> -<h3><a name="4"></a>4. Basic_string size_type and difference_type should be implementation defined</h3> -<p><b>Section:</b> 21.4 [basic.string] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 1997-11-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#basic.string">active issues</a> in [basic.string].</p> -<p><b>View all other</b> <a href="lwg-index.html#basic.string">issues</a> in [basic.string].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>In Morristown we changed the size_type and difference_type typedefs -for all the other containers to implementation defined with a -reference to 23.2 [container.requirements]. This should probably also have been -done for strings. </p> - - -<p><b>Rationale:</b></p> -<p>Not a defect. [Originally classified as a defect, later -reclassified.] basic_string, unlike the other standard library -template containers, is severely constrained by its use of -char_traits. Those types are dictated by the traits class, and are far -from implementation defined.</p> - - - - - -<hr> -<h3><a name="6"></a>6. File position not an offset unimplementable</h3> -<p><b>Section:</b> 27.5.4 [fpos] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 1997-12-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#fpos">issues</a> in [fpos].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Table 88, in I/O, is too strict; it's unimplementable on systems -where a file position isn't just an offset. It also never says just -what fpos<> is really supposed to be. [Here's my summary, which -Jerry agrees is more or less accurate. "I think I now know what -the class really is, at this point: it's a magic cookie that -encapsulates an mbstate_t and a file position (possibly represented as -an fpos_t), it has syntactic support for pointer-like arithmetic, and -implementors are required to have real, not just syntactic, support -for arithmetic." This isn't standardese, of course.] </p> - - -<p><b>Rationale:</b></p> -<p>Not a defect. The LWG believes that the Standard is already clear, -and that the above summary is what the Standard in effect says.</p> - - - - - -<hr> -<h3><a name="10"></a>10. Codecvt<>::do unclear</h3> -<p><b>Section:</b> 22.4.1.5 [locale.codecvt.byname] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 1998-01-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt.byname">issues</a> in [locale.codecvt.byname].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#19">19</a></p> -<p><b>Discussion:</b></p> -<p>Section 22.2.1.5.2 says that codecvt<>::do_in and do_out -should return the value noconv if "no conversion was -needed". However, I don't see anything anywhere that defines what -it means for a conversion to be needed or not needed. I can think of -several circumstances where one might plausibly think that a -conversion is not "needed", but I don't know which one is -intended here. </p> - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="12"></a>12. Way objects hold allocators unclear</h3> -<p><b>Section:</b> 17.6.3.5 [allocator.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Angelika Langer <b>Opened:</b> 1998-02-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#allocator.requirements">active issues</a> in [allocator.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#allocator.requirements">issues</a> in [allocator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>I couldn't find a statement in the standard saying whether the allocator object held by -a container is held as a copy of the constructor argument or whether a pointer of -reference is maintained internal. There is an according statement for compare objects and -how they are maintained by the associative containers, but I couldn't find anything -regarding allocators. </p> - -<p>Did I overlook it? Is it an open issue or known defect? Or is it deliberately left -unspecified? </p> - - -<p><b>Rationale:</b></p> -<p>Not a defect. The LWG believes that the Standard is already -clear. See 23.2 [container.requirements], paragraph 8.</p> - - - - - -<hr> -<h3><a name="43"></a>43. Locale table correction</h3> -<p><b>Section:</b> 22.4.1.5 [locale.codecvt.byname] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Brendan Kehoe <b>Opened:</b> 1998-06-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt.byname">issues</a> in [locale.codecvt.byname].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#33">33</a></p> -<p><b>Discussion:</b></p> - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="45"></a>45. Stringstreams read/write pointers initial position unclear</h3> -<p><b>Section:</b> 27.8.4 [ostringstream] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matthias Mueller <b>Opened:</b> 1998-05-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ostringstream">issues</a> in [ostringstream].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>In a comp.lang.c++.moderated Matthias Mueller wrote:</p> - -<p>"We are not sure how to interpret the CD2 (see 27.3 [iostream.forward], 27.8.4.1 [ostringstream.cons], 27.8.2.1 [stringbuf.cons]) -with respect to the question as to what the correct initial positions -of the write and read pointers of a stringstream should -be."</p> - -<p>"Is it the same to output two strings or to initialize the stringstream with the -first and to output the second?"</p> - -<p><i>[PJ Plauger, Bjarne Stroustrup, Randy Smithey, Sean Corfield, and -Jerry Schwarz have all offered opinions; see reflector messages -lib-6518, 6519, 6520, 6521, 6523, 6524.]</i></p> - - - - -<p><b>Rationale:</b></p> -<p>The LWG believes the Standard is correct as written. The behavior -of stringstreams is consistent with fstreams, and there is a -constructor which can be used to obtain the desired effect. This -behavior is known to be different from strstreams.</p> - - - - - -<hr> -<h3><a name="58"></a>58. Extracting a char from a wide-oriented stream</h3> -<p><b>Section:</b> 27.7.2.2.3 [istream::extractors] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 1998-07-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#istream::extractors">issues</a> in [istream::extractors].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>27.6.1.2.3 has member functions for extraction of signed char and -unsigned char, both singly and as strings. However, it doesn't say -what it means to extract a <tt>char</tt> from a -<tt>basic_streambuf<charT, Traits></tt>. </p> - -<p>basic_streambuf, after all, has no members to extract a char, so -basic_istream must somehow convert from charT to signed char or -unsigned char. The standard doesn't say how it is to perform that -conversion. </p> - - -<p><b>Rationale:</b></p> -<p>The Standard is correct as written. There is no such extractor and -this is the intent of the LWG.</p> - - - - -<hr> -<h3><a name="65"></a>65. Underspecification of strstreambuf::seekoff</h3> -<p><b>Section:</b> D.7.1.3 [depr.strstreambuf.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 1998-08-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#depr.strstreambuf.virtuals">issues</a> in [depr.strstreambuf.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The standard says how this member function affects the current -stream position. (<tt>gptr</tt> or <tt>pptr</tt>) However, it does not -say how this member function affects the beginning and end of the -get/put area. </p> - -<p>This is an issue when seekoff is used to position the get pointer -beyond the end of the current read area. (Which is legal. This is -implicit in the definition of <i>seekhigh</i> in D.7.1, paragraph 4.) -</p> - - -<p><b>Rationale:</b></p> -<p>The LWG agrees that seekoff() is underspecified, but does not wish -to invest effort in this deprecated feature.</p> - - - - - -<hr> -<h3><a name="67"></a>67. Setw useless for strings</h3> -<p><b>Section:</b> 21.4.8.9 [string.io] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Steve Clamage <b>Opened:</b> 1998-07-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string.io">issues</a> in [string.io].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#25">25</a></p> -<p><b>Discussion:</b></p> -<p>In a comp.std.c++ posting Michel Michaud wrote: What -should be output by: </p> - -<pre> string text("Hello"); - cout << '[' << setw(10) << right << text << ']'; -</pre> - -<p>Shouldn't it be:</p> - -<pre> [ Hello]</pre> - -<p>Another person replied: Actually, according to the FDIS, the width -of the field should be the minimum of width and the length of the -string, so the output shouldn't have any padding. I think that this is -a typo, however, and that what is wanted is the maximum of the -two. (As written, setw is useless for strings. If that had been the -intent, one wouldn't expect them to have mentioned using its value.) -</p> - -<p>It's worth pointing out that this is a recent correction anyway; -IIRC, earlier versions of the draft forgot to mention formatting -parameters whatsoever.</p> - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="72"></a>72. Do_convert phantom member function</h3> -<p><b>Section:</b> 22.4.1.4 [locale.codecvt] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Nathan Myers <b>Opened:</b> 1998-08-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt">issues</a> in [locale.codecvt].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#24">24</a></p> -<p><b>Discussion:</b></p> -<p>In 22.4.1.4 [locale.codecvt] par 3, and in 22.4.1.4.2 [locale.codecvt.virtuals] par 8, a nonexistent member function -"do_convert" is mentioned. This member was replaced with -"do_in" and "do_out", the proper referents in the -contexts above.</p> - - -<p><b>Rationale:</b></p> - - - - - -<hr> -<h3><a name="73"></a>73. <tt>is_open</tt> should be const</h3> -<p><b>Section:</b> 27.9.1 [fstreams] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 1998-08-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#fstreams">issues</a> in [fstreams].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Classes <tt>basic_ifstream</tt>, <tt>basic_ofstream</tt>, and -<tt>basic_fstream</tt> all have a member function <tt>is_open</tt>. It -should be a <tt>const</tt> member function, since it does nothing but -call one of <tt>basic_filebuf</tt>'s const member functions. </p> - - -<p><b>Rationale:</b></p> -<p>Not a defect. This is a deliberate feature; const streams would be -meaningless.</p> - - - - -<hr> -<h3><a name="77"></a>77. Valarray operator[] const returning value</h3> -<p><b>Section:</b> 26.6.2.4 [valarray.access] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Levente Farkas <b>Opened:</b> 1998-09-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#valarray.access">issues</a> in [valarray.access].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#389">389</a></p> -<p><b>Discussion:</b></p> -<p>valarray:<br/> -<br/> - <tt>T operator[] (size_t) const;</tt><br/> -<br/> -why not <br/> -<br/> - <tt>const T& operator[] (size_t) const;</tt><br/> -<br/> -as in vector ???<br/> -<br/> -One can't copy even from a const valarray eg:<br/> -<br/> - <tt>memcpy(ptr, &v[0], v.size() * sizeof(double));<br/> -</tt><br/> -[I] find this bug in valarray is very difficult.</p> - - -<p><b>Rationale:</b></p> -<p>The LWG believes that the interface was deliberately designed that -way. That is what valarray was designed to do; that's where the -"value array" name comes from. LWG members further comment -that "we don't want valarray to be a full STL container." -26.6.2.4 [valarray.access] specifies properties that indicate "an -absence of aliasing" for non-constant arrays; this allows -optimizations, including special hardware optimizations, that are not -otherwise possible. </p> - - - - - -<hr> -<h3><a name="81"></a>81. Wrong declaration of slice operations</h3> -<p><b>Section:</b> 26.6.5 [template.slice.array], 26.6.7 [template.gslice.array], 26.6.8 [template.mask.array], 26.6.9 [template.indirect.array] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1998-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#template.slice.array">issues</a> in [template.slice.array].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Isn't the definition of copy constructor and assignment operators wrong? - Instead of</p> - -<pre> slice_array(const slice_array&); - slice_array& operator=(const slice_array&);</pre> - -<p>IMHO they have to be</p> - -<pre> slice_array(const slice_array<T>&); - slice_array& operator=(const slice_array<T>&);</pre> - -<p>Same for gslice_array. </p> - - -<p><b>Rationale:</b></p> -<p>Not a defect. The Standard is correct as written. </p> - - - - -<hr> -<h3><a name="82"></a>82. Missing constant for set elements</h3> -<p><b>Section:</b> 23.2.4 [associative.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1998-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Paragraph 5 specifies:</p> - -<blockquote><p> -For set and multiset the value type is the same as the key type. For -map and multimap it is equal to pair<const Key, T>. -</p></blockquote> - -<p>Strictly speaking, this is not correct because for set and multiset -the value type is the same as the <b>constant</b> key type.</p> - - -<p><b>Rationale:</b></p> -<p>Not a defect. The Standard is correct as written; it uses a -different mechanism (const &) for <tt>set</tt> and -<tt>multiset</tt>. See issue <a href="lwg-defects.html#103">103</a> for a related -issue.</p> - - - - -<hr> -<h3><a name="84"></a>84. Ambiguity with string::insert()</h3> -<p><b>Section:</b> 21.4.5 [string.access] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1998-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string.access">issues</a> in [string.access].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>If I try</p> -<pre> s.insert(0,1,' ');</pre> - -<p> I get an nasty ambiguity. It might be</p> -<pre> s.insert((size_type)0,(size_type)1,(charT)' ');</pre> - -<p>which inserts 1 space character at position 0, or</p> -<pre> s.insert((char*)0,(size_type)1,(charT)' ')</pre> - -<p>which inserts 1 space character at iterator/address 0 (bingo!), or</p> -<pre> s.insert((char*)0, (InputIterator)1, (InputIterator)' ')</pre> - -<p>which normally inserts characters from iterator 1 to iterator ' -'. But according to 23.1.1.9 (the "do the right thing" fix) -it is equivalent to the second. However, it is still ambiguous, -because of course I mean the first!</p> - - -<p><b>Rationale:</b></p> -<p>Not a defect. The LWG believes this is a "genetic -misfortune" inherent in the design of string and thus not a -defect in the Standard as such .</p> - - - - -<hr> -<h3><a name="85"></a>85. String char types</h3> -<p><b>Section:</b> 21 [strings] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1998-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#strings">issues</a> in [strings].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The standard seems not to require that charT is equivalent to -traits::char_type. So, what happens if charT is not equivalent to -traits::char_type?</p> - - -<p><b>Rationale:</b></p> -<p>There is already wording in 21.2 [char.traits] paragraph 3 that -requires them to be the same.</p> - - - - -<hr> -<h3><a name="87"></a>87. Error in description of string::compare()</h3> -<p><b>Section:</b> 21.4.6.8 [string::swap] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1998-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string::swap">issues</a> in [string::swap].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#5">5</a></p> -<p><b>Discussion:</b></p> -<p>The following compare() description is obviously a bug:</p> - -<pre> -int compare(size_type pos, size_type n1, - charT *s, size_type n2 = npos) const; -</pre> - -<p>because without passing n2 it should compare up to the end of the -string instead of comparing npos characters (which throws an -exception) </p> - - -<p><b>Rationale:</b></p> - - - - - -<hr> -<h3><a name="88"></a>88. Inconsistency between string::insert() and string::append()</h3> -<p><b>Section:</b> 21.4.6.4 [string::insert], 21.4.6.2 [string::append] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1998-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string::insert">issues</a> in [string::insert].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Why does </p> -<pre> template<class InputIterator> - basic_string& append(InputIterator first, InputIterator last);</pre> - -<p>return a string, while</p> -<pre> template<class InputIterator> - void insert(iterator p, InputIterator first, InputIterator last);</pre> - -<p>returns nothing ?</p> - - -<p><b>Rationale:</b></p> -<p>The LWG believes this stylistic inconsistency is not sufficiently -serious to constitute a defect.</p> - - - - -<hr> -<h3><a name="89"></a>89. Missing throw specification for string::insert() and string::replace()</h3> -<p><b>Section:</b> 21.4.6.4 [string::insert], 21.4.6.6 [string::replace] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1998-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string::insert">issues</a> in [string::insert].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#83">83</a></p> -<p><b>Discussion:</b></p> -<p>All insert() and replace() members for strings with an iterator as -first argument lack a throw specification. The throw -specification should probably be: length_error if size exceeds -maximum. </p> - - -<p><b>Rationale:</b></p> -<p>Considered a duplicate because it will be solved by the resolution -of issue <a href="lwg-defects.html#83">83</a>.</p> - - - - - -<hr> -<h3><a name="93"></a>93. Incomplete Valarray Subset Definitions</h3> -<p><b>Section:</b> 26.6 [numarray] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1998-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#numarray">issues</a> in [numarray].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>You can easily create subsets, but you can't easily combine them -with other subsets. Unfortunately, you almost always needs an -explicit type conversion to valarray. This is because the standard -does not specify that valarray subsets provide the same operations as -valarrays. </p> - -<p>For example, to multiply two subsets and assign the result to a third subset, you can't -write the following:</p> - -<pre>va[slice(0,4,3)] = va[slice(1,4,3)] * va[slice(2,4,3)];</pre> - -<p>Instead, you have to code as follows:</p> - -<pre>va[slice(0,4,3)] = static_cast<valarray<double> >(va[slice(1,4,3)]) * - static_cast<valarray<double> >(va[slice(2,4,3)]);</pre> - -<p>This is tedious and error-prone. Even worse, it costs performance because each cast -creates a temporary objects, which could be avoided without the cast. </p> - - -<p><b>Proposed resolution:</b></p> -<p>Extend all valarray subset types so that they offer all valarray operations.</p> - - -<p><b>Rationale:</b></p> -<p>This is not a defect in the Standard; it is a request for an extension.</p> - - - - -<hr> -<h3><a name="94"></a>94. May library implementors add template parameters to Standard Library classes?</h3> -<p><b>Section:</b> 17.6.5 [conforming] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 1998-01-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#conforming">issues</a> in [conforming].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Is it a permitted extension for library implementors to add template parameters to -standard library classes, provided that those extra parameters have defaults? For example, -instead of defining <tt>template <class T, class Alloc = allocator<T> > class -vector;</tt> defining it as <tt>template <class T, class Alloc = allocator<T>, -int N = 1> class vector;</tt> </p> - -<p>The standard may well already allow this (I can't think of any way that this extension -could break a conforming program, considering that users are not permitted to -forward-declare standard library components), but it ought to be explicitly permitted or -forbidden. </p> - -<p>comment from Steve Cleary via comp.std.c++:</p> -<blockquote> -<p>I disagree [with the proposed resolution] for the following reason: -consider user library code with template template parameters. For -example, a user library object may be templated on the type of -underlying sequence storage to use (deque/list/vector), since these -classes all take the same number and type of template parameters; this -would allow the user to determine the performance tradeoffs of the -user library object. A similar example is a user library object -templated on the type of underlying set storage (set/multiset) or map -storage (map/multimap), which would allow users to change (within -reason) the semantic meanings of operations on that object.</p> -<p>I think that additional template parameters should be forbidden in -the Standard classes. Library writers don't lose any expressive power, -and can still offer extensions because additional template parameters -may be provided by a non-Standard implementation class:</p> -<pre> - template <class T, class Allocator = allocator<T>, int N = 1> - class __vector - { ... }; - template <class T, class Allocator = allocator<T> > - class vector: public __vector<T, Allocator> - { ... }; -</pre> - -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p>Add a new subclause [presumably 17.4.4.9] following 17.6.5.12 [res.on.exception.handling]:</p> - -<blockquote> - <p>17.4.4.9 Template Parameters</p> <p>A specialization of a - template class described in the C++ Standard Library behaves the - same as if the implementation declares no additional template - parameters.</p> <p>Footnote: Additional template parameters with - default values are thus permitted.</p> -</blockquote> - -<p>Add "template parameters" to the list of subclauses at -the end of 17.6.5 [conforming] paragraph 1.</p> - -<p><i>[Kona: The LWG agreed the standard needs clarification. After -discussion with John Spicer, it seems added template parameters can be -detected by a program using template-template parameters. A straw vote -- "should implementors be allowed to add template -parameters?" found no consensus ; 5 - yes, 7 - no.]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -There is no ambiguity; the standard is clear as written. Library -implementors are not permitted to add template parameters to standard -library classes. This does not fall under the "as if" rule, -so it would be permitted only if the standard gave explicit license -for implementors to do this. This would require a change in the -standard. -</p> - -<p> -The LWG decided against making this change, because it would break -user code involving template template parameters or specializations -of standard library class templates. -</p> - - - - - -<hr> -<h3><a name="95"></a>95. Members added by the implementation</h3> -<p><b>Section:</b> 17.6.5.5 [member.functions] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#member.functions">issues</a> in [member.functions].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>In 17.3.4.4/2 vs 17.3.4.7/0 there is a hole; an implementation could add virtual -members a base class and break user derived classes.</p> - -<p>Example: </p> - -<blockquote> - <pre>// implementation code: -struct _Base { // _Base is in the implementer namespace - virtual void foo (); -}; -class vector : _Base // deriving from a class is allowed -{ ... }; - -// user code: -class vector_checking : public vector -{ - void foo (); // don't want to override _Base::foo () as the - // user doesn't know about _Base::foo () -};</pre> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p>Clarify the wording to make the example illegal.</p> - - -<p><b>Rationale:</b></p> -<p>This is not a defect in the Standard. The example is already -illegal. See 17.6.5.5 [member.functions] paragraph 2.</p> - - - - -<hr> -<h3><a name="96"></a>96. Vector<bool> is not a container</h3> -<p><b>Section:</b> 23.3.6 [vector] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#vector">issues</a> in [vector].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><tt>vector<bool></tt> is not a container as its reference and -pointer types are not references and pointers. </p> - -<p>Also it forces everyone to have a space optimization instead of a -speed one.</p> - -<p><b>See also:</b> 99-0008 == N1185 Vector<bool> is -Nonconforming, Forces Optimization Choice.</p> - -<p><i>[In Santa Cruz the LWG felt that this was Not A Defect.]</i></p> - - -<p><i>[In Dublin many present felt that failure to meet Container -requirements was a defect. There was disagreement as to whether -or not the optimization requirements constituted a defect.]</i></p> - - -<p><i>[The LWG looked at the following resolutions in some detail: -<br/> - * Not A Defect.<br/> - * Add a note explaining that vector<bool> does not meet -Container requirements.<br/> - * Remove vector<bool>.<br/> - * Add a new category of container requirements which -vector<bool> would meet.<br/> - * Rename vector<bool>.<br/> -<br/> -No alternative had strong, wide-spread, support and every alternative -had at least one "over my dead body" response.<br/> -<br/> -There was also mention of a transition scheme something like (1) add -vector_bool and deprecate vector<bool> in the next standard. (2) -Remove vector<bool> in the following standard.]</i></p> - - -<p><i>[Modifying container requirements to permit returning proxies -(thus allowing container requirements conforming vector<bool>) -was also discussed.]</i></p> - - -<p><i>[It was also noted that there is a partial but ugly workaround in -that vector<bool> may be further specialized with a customer -allocator.]</i></p> - - -<p><i>[Kona: Herb Sutter presented his paper J16/99-0035==WG21/N1211, -<tt>vector<bool></tt>: More Problems, Better Solutions. Much discussion -of a two step approach: a) deprecate, b) provide replacement under a -new name. LWG straw vote on that: 1-favor, 11-could live with, 2-over -my dead body. This resolution was mentioned in the LWG report to the -full committee, where several additional committee members indicated -over-my-dead-body positions.]</i></p> - - -<p>Discussed at Lillehammer. General agreement that we should - deprecate <tt>vector<bool></tt> and introduce this functionality under - a different name, e.g. <tt>bit_vector</tt>. This might make it possible to - remove the <tt>vector<bool></tt> specialization in the standard that comes - after C++0x. There was also a suggestion that - in C++0x we could additional say that it's implementation defined - whether <tt>vector<bool></tt> refers to the specialization or to the - primary template, but there wasn't general agreement that this was a - good idea.</p> - -<p>We need a paper for the new <tt>bit_vector</tt> class.</p> - -<p><i>[ -Batavia: -]</i></p> - -<blockquote><p> -The LWG feels we need something closer to SGI's <tt>bitvector</tt> to ease migration -from <tt>vector<bool></tt>. Although some of the funcitonality from -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2050.pdf">N2050</a> -could well be used in such a template. The concern is easing the API migration for those -users who want to continue using a bit-packed container. Alan and Beman to work. -</p></blockquote> - -<p><i>[ -Post Summit Alisdair adds: -]</i></p> - - -<blockquote> -<p> -<tt>vector<bool></tt> is now a conforming container under the revised terms of C++0x, -which supports containers of proxies. -</p> -<p> -Recommend NAD. -</p> -<p> -Two issues remain: -</p> -<p> -i/ premature optimization in the specification. -There is still some sentiment that deprecation is the correct way to go, -although it is still not clear what it would mean to deprecate a single -specialization of a template. -</p> -<p> -Recommend: Create a new issue for the discussion, leave as Open. -</p> -<p> -ii/ Request for a new bitvector class to guarantee the optimization, perhaps -with a better tuned interface. -</p> -<p> -This is a clear extension request that may be handled via a future TR. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We note that most of this issue has become moot over time, -and agree with Alisdair's recommendations. -Move to NAD Future for reconsideration of part (ii). -</p></blockquote> - -<p><i>[ -2009-07-29 Alisdair reopens: -]</i></p> - - -<blockquote> -<p> -This infamous issue was closed as NAD Future when concepts introduced -support for proxy iterators, so the only remaining requirement was to -provide a better type to support bitsets of dynamic length. I fear we -must re-open this issue until the post-concept form of iterators is -available, and hopefully will support the necessary proxy functionality -to allow us to close this issue as NAD. -</p> - -<p> -I recommend we spawn a separate issue (<a href="lwg-active.html#1184">1184</a>) requesting a dynamic length bitset -and pre-emptively file it as NAD Future. It is difficult to resolve #96 -when it effectively contains two separate sub-issues. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD, and give rationale. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -We now have: -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2050.pdf">N2050</a> -and -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2160.html">N2160</a>. -</p> - - - -<p><b>Rationale:</b></p> -<p> -We want to support proxy iterators but that is going to be separate -work. Don't want to see this issue come back in these kinds of terms. -We're interested in a separate container, and proxy iterators, but both -of those are separate issues. -</p> -<p> -We've looked at a lot of ways to fix this that would be close to this, -but those things would break existing code. Attempts to fix this -directly have not been tractable, and removing it has not been -tractable. Therefore we are closing. -</p> - - - - - -<hr> -<h3><a name="97"></a>97. Insert inconsistent definition</h3> -<p><b>Section:</b> 23 [containers] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#containers">active issues</a> in [containers].</p> -<p><b>View all other</b> <a href="lwg-index.html#containers">issues</a> in [containers].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><tt>insert(iterator, const value_type&)</tt> is defined both on -sequences and on set, with unrelated semantics: insert here (in -sequences), and insert with hint (in associative containers). They -should have different names (B.S. says: do not abuse overloading).</p> - - -<p><b>Rationale:</b></p> -<p>This is not a defect in the Standard. It is a genetic misfortune of -the design, for better or for worse.</p> - - - - -<hr> -<h3><a name="99"></a>99. Reverse_iterator comparisons completely wrong</h3> -<p><b>Section:</b> 24.5.1.3.13 [reverse.iter.op==] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The <, >, <=, >= comparison operator are wrong: they -return the opposite of what they should.</p> - -<p>Note: same problem in CD2, these were not even defined in CD1. SGI -STL code is correct; this problem is known since the Morristown -meeting but there it was too late</p> - - -<p><b>Rationale:</b></p> -<p>This is not a defect in the Standard. A careful reading shows the Standard is correct -as written. A review of several implementations show that they implement -exactly what the Standard says.</p> - - - - -<hr> -<h3><a name="100"></a>100. Insert iterators/ostream_iterators overconstrained</h3> -<p><b>Section:</b> 24.5.2 [insert.iterators], 24.6.4 [ostreambuf.iterator] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#insert.iterators">issues</a> in [insert.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Overspecified For an insert iterator it, the expression *it is -required to return a reference to it. This is a simple possible -implementation, but as the SGI STL documentation says, not the only -one, and the user should not assume that this is the case.</p> - - -<p><b>Rationale:</b></p> -<p>The LWG believes this causes no harm and is not a defect in the -standard. The only example anyone could come up with caused some -incorrect code to work, rather than the other way around.</p> - - - - - -<hr> -<h3><a name="101"></a>101. No way to free storage for vector and deque</h3> -<p><b>Section:</b> 23.3.6 [vector], 23.3.2 [array] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#vector">issues</a> in [vector].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p>Reserve can not free storage, unlike string::reserve</p> - -<p><i>[ -2010-02-13 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -This issue has been revisited and addressed (<a href="lwg-defects.html#755">755</a>, <a href="lwg-defects.html#850">850</a>). This issues should be reclassified to NAD Editorial to reflect -this action. -</p> -</blockquote> - - - -<p><b>Rationale:</b></p> -<p>This is not a defect in the Standard. The LWG has considered this -issue in the past and sees no need to change the Standard. Deque has -no reserve() member function. For vector, shrink-to-fit can be -expressed in a single line of code (where <tt>v</tt> is -<tt>vector<T></tt>): -</p> - -<blockquote> - <p><tt>vector<T>(v).swap(v); // shrink-to-fit v</tt></p> -</blockquote> - - - - - -<hr> -<h3><a name="102"></a>102. Bug in insert range in associative containers</h3> -<p><b>Section:</b> 23.2.4 [associative.reqmts] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#264">264</a></p> -<p><b>Discussion:</b></p> -<p>Table 69 of Containers say that a.insert(i,j) is linear if [i, j) is ordered. It seems -impossible to implement, as it means that if [i, j) = [x], insert in an associative -container is O(1)!</p> - - -<p><b>Proposed resolution:</b></p> -<p>N+log (size()) if [i,j) is sorted according to value_comp()</p> - - -<p><b>Rationale:</b></p> -<p>Subsumed by issue <a href="lwg-defects.html#264">264</a>.</p> - - - - - -<hr> -<h3><a name="104"></a>104. Description of basic_string::operator[] is unclear</h3> -<p><b>Section:</b> 21.4.4 [string.capacity] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string.capacity">issues</a> in [string.capacity].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>It is not clear that undefined behavior applies when pos == size () -for the non const version.</p> - - -<p><b>Proposed resolution:</b></p> -<p>Rewrite as: Otherwise, if pos > size () or pos == size () and -the non-const version is used, then the behavior is undefined.</p> - - -<p><b>Rationale:</b></p> -<p>The Standard is correct. The proposed resolution already appears in -the Standard.</p> - - - - -<hr> -<h3><a name="105"></a>105. fstream ctors argument types desired</h3> -<p><b>Section:</b> 27.9 [file.streams] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-closed.html#454">454</a></p> -<p><b>Discussion:</b></p> - - -<p>fstream ctors take a const char* instead of string.<br/> -fstream ctors can't take wchar_t</p> - -<p>An extension to add a const wchar_t* to fstream would make the -implementation non conforming.</p> - - -<p><b>Rationale:</b></p> -<p>This is not a defect in the Standard. It might be an -interesting extension for the next Standard. </p> - - - - -<hr> -<h3><a name="107"></a>107. Valarray constructor is strange</h3> -<p><b>Section:</b> 26.6.2 [template.valarray] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> AFNOR <b>Opened:</b> 1998-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#template.valarray">issues</a> in [template.valarray].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The order of the arguments is (elem, size) instead of the normal -(size, elem) in the rest of the library. Since elem often has an -integral or floating point type, both types are convertible to each -other and reversing them leads to a well formed program.</p> - - -<p><b>Proposed resolution:</b></p> -<p>Inverting the arguments could silently break programs. Introduce -the two signatures (const T&, size_t) and (size_t, const T&), -but make the one we do not want private so errors result in a -diagnosed access violation. This technique can also be applied to STL -containers.</p> - - -<p><b>Rationale:</b></p> -<p>The LWG believes that while the order of arguments is unfortunate, -it does not constitute a defect in the standard. The LWG believes that -the proposed solution will not work for valarray<size_t> and -perhaps other cases.</p> - - - - -<hr> -<h3><a name="111"></a>111. <tt>istreambuf_iterator::equal</tt> overspecified, inefficient</h3> -<p><b>Section:</b> 24.6.3.5 [istreambuf.iterator::equal] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nathan Myers <b>Opened:</b> 1998-10-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#istreambuf.iterator::equal">issues</a> in [istreambuf.iterator::equal].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The member <tt>istreambuf_iterator<>::equal</tt> is specified to be -unnecessarily inefficient. While this does not affect the efficiency -of conforming implementations of iostreams, because they can -"reach into" the iterators and bypass this function, it does -affect users who use <tt>istreambuf_iterators</tt>. </p> - -<p>The inefficiency results from a too-scrupulous definition, which -requires a "true" result if neither iterator is at eof. In -practice these iterators can only usefully be compared with the -"eof" value, so the extra test implied provides no benefit, -but slows down users' code. </p> - -<p>The solution is to weaken the requirement on the function to return -true only if both iterators are at eof. </p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Reopened by Alisdair. -</p></blockquote> - -<p><i>[ -Post Summit Daniel adds: -]</i></p> - - -<blockquote> -<p> -Recommend NAD. The proposed wording would violate the axioms of -concept requirement <tt>EqualityComparable</tt> axioms as part of concept <tt>InputIterator</tt> -and more specifically it would violate the explicit wording of -24.2.3 [input.iterators]/7: -</p> - -<blockquote><p> -If two iterators <tt>a</tt> and <tt>b</tt> of the same type are equal, then either <tt>a</tt> -and <tt>b</tt> are both dereferenceable or else neither is dereferenceable. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Agree NAD. -</p></blockquote> - -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p>Replace 24.6.3.5 [istreambuf.iterator::equal], paragraph 1, </p> - -<blockquote> - <p>-1- <i>Returns</i>: true if and only if both iterators are at end-of-stream, or neither is at - end-of-stream, regardless of what streambuf object they use. </p> -</blockquote> - -<p>with</p> - -<blockquote> - <p>-1- <i>Returns</i>: true if and only if both iterators are at - end-of-stream, regardless of what streambuf object they use. </p> -</blockquote> - - - -<p><b>Rationale:</b></p> -<p>It is not clear that this is a genuine defect. Additionally, the -LWG was reluctant to make a change that would result in -<tt>operator==</tt> not being a equivalence relation. One consequence of -this change is that an algorithm that's passed the range <tt>[i, i)</tt> -would no longer treat it as an empty range.</p> - - - - - -<hr> -<h3><a name="113"></a>113. Missing/extra iostream sync semantics</h3> -<p><b>Section:</b> 27.7.2.1 [istream], 27.7.2.3 [istream.unformatted] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Steve Clamage <b>Opened:</b> 1998-10-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#istream">issues</a> in [istream].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>In 27.6.1.1, class basic_istream has a member function sync, described in 27.6.1.3, -paragraph 36. </p> - -<p>Following the chain of definitions, I find that the various sync functions have defined -semantics for output streams, but no semantics for input streams. On the other hand, -basic_ostream has no sync function. </p> - -<p>The sync function should at minimum be added to basic_ostream, for internal -consistency. </p> - -<p>A larger question is whether sync should have assigned semantics for input streams. </p> - -<p>Classic iostreams said streambuf::sync flushes pending output and attempts to return -unread input characters to the source. It is a protected member function. The filebuf -version (which is public) has that behavior (it backs up the read pointer). Class -strstreambuf does not override streambuf::sync, and so sync can't be called on a -strstream. </p> - -<p>If we can add corresponding semantics to the various sync functions, we should. If not, -we should remove sync from basic_istream.</p> - - -<p><b>Rationale:</b></p> -<p>A sync function is not needed in basic_ostream because the flush function provides the -desired functionality.</p> - -<p>As for the other points, the LWG finds the standard correct as written.</p> - - - - - -<hr> -<h3><a name="116"></a>116. bitset cannot be constructed with a const char*</h3> -<p><b>Section:</b> 20.6 [template.bitset] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Judy Ward <b>Opened:</b> 1998-11-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#template.bitset">active issues</a> in [template.bitset].</p> -<p><b>View all other</b> <a href="lwg-index.html#template.bitset">issues</a> in [template.bitset].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#778">778</a></p> -<p><b>Discussion:</b></p> - - - -<p>The following code does not compile with the EDG compiler:</p> - -<blockquote> - <pre>#include <bitset> -using namespace std; -bitset<32> b("111111111");</pre> -</blockquote> - -<p>If you cast the ctor argument to a string, i.e.:</p> - -<blockquote> - <pre>bitset<32> b(string("111111111"));</pre> -</blockquote> - -<p>then it will compile. The reason is that bitset has the following templatized -constructor:</p> - -<blockquote> - <pre>template <class charT, class traits, class Allocator> -explicit bitset (const basic_string<charT, traits, Allocator>& str, ...);</pre> -</blockquote> - -<p>According to the compiler vendor, Steve Adamcyk at EDG, the user -cannot pass this template constructor a <tt>const char*</tt> and -expect a conversion to <tt>basic_string</tt>. The reason is -"When you have a template constructor, it can get used in -contexts where type deduction can be done. Type deduction basically -comes up with exact matches, not ones involving conversions." -</p> - -<p>I don't think the intention when this constructor became -templatized was for construction from a <tt>const char*</tt> to no -longer work.</p> - - -<p><b>Proposed resolution:</b></p> -<p>Add to 20.6 [template.bitset] a bitset constructor declaration</p> - -<blockquote> - <pre>explicit bitset(const char*);</pre> -</blockquote> - -<p>and in Section 20.6.1 [bitset.cons] add:</p> - -<blockquote> - <pre>explicit bitset(const char* str);</pre> - <p>Effects: <br/> - Calls <tt>bitset((string) str, 0, string::npos);</tt></p> -</blockquote> - - -<p><b>Rationale:</b></p> -<p>Although the problem is real, the standard is designed that way so -it is not a defect. Education is the immediate workaround. A future -standard may wish to consider the Proposed Resolution as an -extension.</p> - - - - - -<hr> -<h3><a name="121"></a>121. Detailed definition for ctype<wchar_t> specialization</h3> -<p><b>Section:</b> 22.3.1.1.1 [locale.category] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Judy Ward <b>Opened:</b> 1998-12-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.category">issues</a> in [locale.category].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Section 22.1.1.1.1 has the following listed in Table 51: ctype<char> , -ctype<wchar_t>. </p> - -<p>Also Section 22.4.1.1 [locale.ctype] says: </p> - -<blockquote> - <p>The instantiations required in Table 51 (22.1.1.1.1) namely ctype<char> and - ctype<wchar_t> , implement character classing appropriate to the implementation's - native character set. </p> -</blockquote> - -<p>However, Section 22.4.1.3 [facet.ctype.special] -only has a detailed description of the ctype<char> specialization, not the -ctype<wchar_t> specialization. </p> - - -<p><b>Proposed resolution:</b></p> -<p>Add the ctype<wchar_t> detailed class description to Section -22.4.1.3 [facet.ctype.special]. </p> - - -<p><b>Rationale:</b></p> -<p>Specialization for wchar_t is not needed since the default is acceptable.</p> - - - - - -<hr> -<h3><a name="128"></a>128. Need open_mode() function for file stream, string streams, file buffers, and string buffers</h3> -<p><b>Section:</b> 27.8 [string.streams], 27.9 [file.streams] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Angelika Langer <b>Opened:</b> 1999-02-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string.streams">issues</a> in [string.streams].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The following question came from Thorsten Herlemann:</p> - -<blockquote> - <p>You can set a mode when constructing or opening a file-stream or - filebuf, e.g. ios::in, ios::out, ios::binary, ... But how can I get - that mode later on, e.g. in my own operator << or operator - >> or when I want to check whether a file-stream or - file-buffer object passed as parameter is opened for input or output - or binary? Is there no possibility? Is this a design-error in the - standard C++ library? </p> -</blockquote> - -<p>It is indeed impossible to find out what a stream's or stream -buffer's open mode is, and without that knowledge you don't know -how certain operations behave. Just think of the append mode. </p> - -<p>Both streams and stream buffers should have a <tt>mode()</tt> function that returns the -current open mode setting. </p> - -<p><i>[ -post Bellevue: Alisdair requested to re-Open. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -Neither Howard nor Bill has received a customer request for this. -</p> -<p> -No consensus for change. The programmer can save this information to the side. -</p> -<p> -Moved to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p>For stream buffers, add a function to the base class as a non-virtual function -qualified as const to 27.6.3 [streambuf]:</p> - -<p> <tt>openmode mode() const</tt>;</p> - -<p><b> Returns</b> the current open mode.</p> - -<p>With streams, I'm not sure what to suggest. In principle, the mode -could already be returned by <tt>ios_base</tt>, but the mode is only -initialized for file and string stream objects, unless I'm overlooking -anything. For this reason it should be added to the most derived -stream classes. Alternatively, it could be added to <tt>basic_ios</tt> -and would be default initialized in <tt>basic_ios<>::init()</tt>.</p> - - -<p><b>Rationale:</b></p> -<p>This might be an interesting extension for some future, but it is -not a defect in the current standard. The Proposed Resolution is -retained for future reference.</p> - - - - - -<hr> -<h3><a name="131"></a>131. list::splice throws nothing</h3> -<p><b>Section:</b> 23.3.5.5 [list.ops] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 1999-03-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#list.ops">issues</a> in [list.ops].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>What happens if a splice operation causes the size() of a list to grow -beyond max_size()?</p> - - -<p><b>Rationale:</b></p> -<p>Size() cannot grow beyond max_size(). </p> - - - - - -<hr> -<h3><a name="135"></a>135. basic_iostream doubly initialized</h3> -<p><b>Section:</b> 27.7.2.5.1 [iostream.cons] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 1999-03-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>-1- Effects Constructs an object of class basic_iostream, assigning -initial values to the base classes by calling -basic_istream<charT,traits>(sb) (lib.istream) and -basic_ostream<charT,traits>(sb) (lib.ostream)</p> - -<p>The called for basic_istream and basic_ostream constructors call -init(sb). This means that the basic_iostream's virtual base class is -initialized twice.</p> - - -<p><b>Proposed resolution:</b></p> -<p>Change 27.6.1.5.1, paragraph 1 to:</p> - -<p>-1- Effects Constructs an object of class basic_iostream, assigning -initial values to the base classes by calling -basic_istream<charT,traits>(sb) (lib.istream).</p> - - -<p><b>Rationale:</b></p> -<p>The LWG agreed that the <tt> init()</tt> function is called -twice, but said that this is harmless and so not a defect in the -standard.</p> - - - - -<hr> -<h3><a name="138"></a>138. Class <tt>ctype_byname<char></tt> redundant and misleading</h3> -<p><b>Section:</b> 22.4.1.4 [locale.codecvt] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Angelika Langer <b>Opened:</b> 1999-03-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt">issues</a> in [locale.codecvt].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Section 22.4.1.4 [locale.codecvt] specifies that -<tt>ctype_byname<char></tt> must be a specialization of the <tt>ctype_byname</tt> -template.</p> - -<p>It is common practice in the standard that specializations of class templates are only -mentioned where the interface of the specialization deviates from the interface of the -template that it is a specialization of. Otherwise, the fact whether or not a required -instantiation is an actual instantiation or a specialization is left open as an -implementation detail. </p> - -<p>Clause 22.2.1.4 deviates from that practice and for that reason is misleading. The -fact, that <tt>ctype_byname<char></tt> is specified as a specialization suggests that there -must be something "special" about it, but it has the exact same interface as the -<tt>ctype_byname</tt> template. Clause 22.2.1.4 does not have any explanatory value, is at best -redundant, at worst misleading - unless I am missing anything. </p> - -<p>Naturally, an implementation will most likely implement <tt>ctype_byname<char></tt> as a -specialization, because the base class <tt>ctype<char></tt> is a specialization with an -interface different from the <tt>ctype</tt> template, but that's an implementation detail and need -not be mentioned in the standard. </p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Reopened by Alisdair. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Moved to NAD. -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p> The standard as written is mildly misleading, but the correct fix -is to deal with the underlying problem in the <tt>ctype_byname</tt> base class, -not in the specialization. See issue <a href="lwg-defects.html#228">228</a>.</p> - - - - -<hr> -<h3><a name="140"></a>140. map<Key, T>::value_type does not satisfy the assignable requirement</h3> -<p><b>Section:</b> 23.4.4 [map] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Mark Mitchell <b>Opened:</b> 1999-04-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#map">issues</a> in [map].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<blockquote> - <p>23.2 [container.requirements]<br/> - <br/> - expression return type - pre/post-condition<br/> - ------------- ----------- - -------------------<br/> - X::value_type T - - T is assignable<br/> - <br/> - 23.4.4 [map]<br/> - <br/> - A map satisfies all the requirements of a container.<br/> - <br/> - For a map<Key, T> ... the value_type is pair<const Key, T>.</p> -</blockquote> - -<p>There's a contradiction here. In particular, `pair<const Key, -T>' is not assignable; the `const Key' cannot be assigned -to. So, map<Key, T>::value_type does not satisfy the -assignable requirement imposed by a container.</p> - -<p><i>[See issue <a href="lwg-defects.html#103">103</a> for the slightly related issue of -modification of set keys.]</i></p> - - - -<p><b>Rationale:</b></p> -<p>The LWG believes that the standard is inconsistent, but that this -is a design problem rather than a strict defect. May wish to -reconsider for the next standard.</p> - - - - -<hr> -<h3><a name="143"></a>143. C .h header wording unclear</h3> -<p><b>Section:</b> D.5 [depr.c.headers] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Christophe de Dinechin <b>Opened:</b> 1999-05-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>[depr.c.headers] paragraph 2 reads:</p> - -<blockquote> - -<p>Each C header, whose name has the form name.h, behaves as if each -name placed in the Standard library namespace by the corresponding -cname header is also placed within the namespace scope of the -namespace std and is followed by an explicit using-declaration -(_namespace.udecl_)</p> - -</blockquote> - -<p>I think it should mention the global name space somewhere... -Currently, it indicates that name placed in std is also placed in -std...</p> - -<p>I don't know what is the correct wording. For instance, if struct -tm is defined in time.h, ctime declares std::tm. However, the current -wording seems ambiguous regarding which of the following would occur -for use of both ctime and time.h:</p> - -<blockquote> - <pre>// version 1: -namespace std { - struct tm { ... }; -} -using std::tm; - -// version 2: -struct tm { ... }; -namespace std { - using ::tm; -} - -// version 3: -struct tm { ... }; -namespace std { - struct tm { ... }; -}</pre> -</blockquote> - -<p>I think version 1 is intended.</p> - -<p><i>[Kona: The LWG agreed that the wording is not clear. It also -agreed that version 1 is intended, version 2 is not equivalent to -version 1, and version 3 is clearly not intended. The example below -was constructed by Nathan Myers to illustrate why version 2 is not -equivalent to version 1.</i></p> - -<p><i>Although not equivalent, the LWG is unsure if (2) is enough of -a problem to be prohibited. Points discussed in favor of allowing -(2):</i></p> - -<blockquote> - <ul> - <li><i>It may be a convenience to implementors.</i></li> - <li><i>The only cases that fail are structs, of which the C library - contains only a few.</i></li> - </ul> -</blockquote> - -<p><i>]</i></p> - -<p><b>Example:</b></p> - -<blockquote> - -<pre>#include <time.h> -#include <utility> - -int main() { - std::tm * t; - make_pair( t, t ); // okay with version 1 due to Koenig lookup - // fails with version 2; make_pair not found - return 0; -}</pre> - -</blockquote> - - -<p><b>Proposed resolution:</b></p> - -<p>Replace D.5 [depr.c.headers] paragraph 2 with:</p> - -<blockquote> - -<p> Each C header, whose name has the form name.h, behaves as if each -name placed in the Standard library namespace by the corresponding -cname header is also placed within the namespace scope of the -namespace std by name.h and is followed by an explicit -using-declaration (_namespace.udecl_) in global scope.</p> - -</blockquote> - - - -<p><b>Rationale:</b></p> -<p> The current wording in the standard is the result of a difficult -compromise that averted delay of the standard. Based on discussions -in Tokyo it is clear that there is no still no consensus on stricter -wording, so the issue has been closed. It is suggested that users not -write code that depends on Koenig lookup of C library functions.</p> - - - - -<hr> -<h3><a name="145"></a>145. adjustfield lacks default value</h3> -<p><b>Section:</b> 27.5.5.2 [basic.ios.cons] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Angelika Langer <b>Opened:</b> 1999-05-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#basic.ios.cons">issues</a> in [basic.ios.cons].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>There is no initial value for the adjustfield defined, although -many people believe that the default adjustment were right. This is a -common misunderstanding. The standard only defines that, if no -adjustment is specified, all the predefined inserters must add fill -characters before the actual value, which is "as if" the -right flag were set. The flag itself need not be set.</p> - -<p>When you implement a user-defined inserter you cannot rely on right -being the default setting for the adjustfield. Instead, you must be -prepared to find none of the flags set and must keep in mind that in -this case you should make your inserter behave "as if" the -right flag were set. This is surprising to many people and complicates -matters more than necessary.</p> - -<p>Unless there is a good reason why the adjustfield should not be -initialized I would suggest to give it the default value that -everybody expects anyway.</p> - - - -<p><b>Rationale:</b></p> -<p>This is not a defect. It is deliberate that the default is no bits -set. Consider Arabic or Hebrew, for example. See 22.4.2.2.2 [facet.num.put.virtuals] paragraph 19, Table 61 - Fill padding.</p> - - - - -<hr> -<h3><a name="157"></a>157. Meaningless error handling for <tt>pword()</tt> and <tt>iword()</tt></h3> -<p><b>Section:</b> 27.5.3.5 [ios.base.storage] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Dietmar Kühl <b>Opened:</b> 1999-07-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ios.base.storage">issues</a> in [ios.base.storage].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#41">41</a></p> -<p><b>Discussion:</b></p> -<p>According to paragraphs 2 and 4 of 27.5.3.5 [ios.base.storage], the -functions <tt>iword()</tt> and <tt>pword()</tt> "set the -<tt>badbit</tt> (which might throw an exception)" on -failure. ... but what does it mean for <tt>ios_base</tt> to set the -<tt>badbit</tt>? The state facilities of the IOStream library are -defined in <tt>basic_ios</tt>, a derived class! It would be possible -to attempt a down cast but then it would be necessary to know the -character type used...</p> - - -<p><b>Rationale:</b></p> - - - - - -<hr> -<h3><a name="162"></a>162. Really "formatted input functions"?</h3> -<p><b>Section:</b> 27.7.2.2.3 [istream::extractors] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Dietmar Kühl <b>Opened:</b> 1999-07-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#istream::extractors">issues</a> in [istream::extractors].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#60">60</a></p> -<p><b>Discussion:</b></p> -<p>It appears to be somewhat nonsensical to consider the functions -defined in the paragraphs 1 to 5 to be "Formatted input -function" but since these functions are defined in a section -labeled "Formatted input functions" it is unclear to me -whether these operators are considered formatted input functions which -have to conform to the "common requirements" from 27.7.2.2.1 [istream.formatted.reqmts]: If this is the case, all manipulators, not just -<tt>ws</tt>, would skip whitespace unless <tt>noskipws</tt> is set -(... but setting <tt>noskipws</tt> using the manipulator syntax would -also skip whitespace :-)</p> - -<p>See also issue <a href="lwg-closed.html#166">166</a> for the same problem in formatted -output</p> - - -<p><b>Rationale:</b></p> - - - - - -<hr> -<h3><a name="163"></a>163. Return of <tt>gcount()</tt> after a call to <tt>gcount</tt></h3> -<p><b>Section:</b> 27.7.2.3 [istream.unformatted] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Dietmar Kühl <b>Opened:</b> 1999-07-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#istream.unformatted">active issues</a> in [istream.unformatted].</p> -<p><b>View all other</b> <a href="lwg-index.html#istream.unformatted">issues</a> in [istream.unformatted].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#60">60</a></p> -<p><b>Discussion:</b></p> -<p>It is not clear which functions are to be considered unformatted -input functions. As written, it seems that all functions in 27.7.2.3 [istream.unformatted] are unformatted input functions. However, it does not -really make much sense to construct a sentry object for -<tt>gcount()</tt>, <tt>sync()</tt>, ... Also it is unclear what -happens to the <tt>gcount()</tt> if eg. <tt>gcount()</tt>, -<tt>putback()</tt>, <tt>unget()</tt>, or <tt>sync()</tt> is called: -These functions don't extract characters, some of them even -"unextract" a character. Should this still be reflected in -<tt>gcount()</tt>? Of course, it could be read as if after a call to -<tt>gcount()</tt> <tt>gcount()</tt> return <tt>0</tt> (the last -unformatted input function, <tt>gcount()</tt>, didn't extract any -character) and after a call to <tt>putback()</tt> <tt>gcount()</tt> -returns <tt>-1</tt> (the last unformatted input function -<tt>putback()</tt> did "extract" back into the -stream). Correspondingly for <tt>unget()</tt>. Is this what is -intended? If so, this should be clarified. Otherwise, a corresponding -clarification should be used.</p> - - -<p><b>Rationale:</b></p> - - - - - -<hr> -<h3><a name="166"></a>166. Really "formatted output functions"?</h3> -<p><b>Section:</b> 27.7.3.6.3 [ostream.inserters] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Dietmar Kühl <b>Opened:</b> 1999-07-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#60">60</a></p> -<p><b>Discussion:</b></p> -<p>From 27.7.3.6.1 [ostream.formatted.reqmts] it appears that all the functions -defined in 27.7.3.6.3 [ostream.inserters] have to construct a -<tt>sentry</tt> object. Is this really intended?</p> - -<p>This is basically the same problem as issue <a href="lwg-closed.html#162">162</a> but -for output instead of input.</p> - - -<p><b>Rationale:</b></p> - - - - - -<hr> -<h3><a name="177"></a>177. Complex operators cannot be explicitly instantiated</h3> -<p><b>Section:</b> 26.4.6 [complex.ops] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Judy Ward <b>Opened:</b> 1999-07-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#complex.ops">issues</a> in [complex.ops].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>A user who tries to explicitly instantiate a complex non-member operator will -get compilation errors. Below is a simplified example of the reason why. The -problem is that iterator_traits cannot be instantiated on a non-pointer type -like float, yet when the compiler is trying to decide which operator+ needs to -be instantiated it must instantiate the declaration to figure out the first -argument type of a reverse_iterator operator.</p> -<pre>namespace std { -template <class Iterator> -struct iterator_traits -{ - typedef typename Iterator::value_type value_type; -}; - -template <class T> class reverse_iterator; - -// reverse_iterator operator+ -template <class T> -reverse_iterator<T> operator+ -(typename iterator_traits<T>::difference_type, const reverse_iterator<T>&); - -template <class T> struct complex {}; - -// complex operator + -template <class T> -complex<T> operator+ (const T& lhs, const complex<T>& rhs) -{ return complex<T>();} -} - -// request for explicit instantiation -template std::complex<float> std::operator+<float>(const float&, - const std::complex<float>&);</pre> -<p>See also c++-stdlib reflector messages: lib-6814, 6815, 6816.</p> - - -<p><b>Rationale:</b></p> -<p>Implementors can make minor changes and the example will -work. Users are not affected in any case.</p> <p>According to John -Spicer, It is possible to explicitly instantiate these operators using -different syntax: change "std::operator+<float>" to -"std::operator+".</p> - -<p>The proposed resolution of issue 120 is that users will not be able -to explicitly instantiate standard library templates. If that -resolution is accepted then library implementors will be the only ones -that will be affected by this problem, and they must use the indicated -syntax.</p> - - - - -<hr> -<h3><a name="178"></a>178. Should clog and cerr initially be tied to cout?</h3> -<p><b>Section:</b> 27.4.2 [narrow.stream.objects] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Judy Ward <b>Opened:</b> 1999-07-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#narrow.stream.objects">issues</a> in [narrow.stream.objects].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Section 27.3.1 says "After the object cerr is initialized, -cerr.flags() & unitbuf is nonzero. Its state is otherwise the same as -required for ios_base::init (lib.basic.ios.cons). It doesn't say -anything about the the state of clog. So this means that calling -cerr.tie() and clog.tie() should return 0 (see Table 89 for -ios_base::init effects). -</p> -<p> -Neither of the popular standard library implementations -that I tried does this, they both tie cerr and clog -to &cout. I would think that would be what users expect. -</p> - - -<p><b>Rationale:</b></p> -<p>The standard is clear as written.</p> -<p>27.3.1/5 says that "After the object cerr is initialized, cerr.flags() -& unitbuf is nonzero. Its state is otherwise the same as required for -ios_base::init (27.4.4.1)." Table 89 in 27.4.4.1, which gives the -postconditions of basic_ios::init(), says that tie() is 0. (Other issues correct -ios_base::init to basic_ios::init().)</p> - - - - -<hr> -<h3><a name="188"></a>188. valarray helpers missing augmented assignment operators</h3> -<p><b>Section:</b> 26.6.2.7 [valarray.cassign] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Gabriel Dos Reis <b>Opened:</b> 1999-08-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#valarray.cassign">issues</a> in [valarray.cassign].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>26.5.2.6 defines augmented assignment operators -valarray<T>::op=(const T&), but fails to provide -corresponding versions for the helper classes. Thus making the -following illegal:</p> -<blockquote> -<pre>#include <valarray> - -int main() -{ -std::valarray<double> v(3.14, 1999); - -v[99] *= 2.0; // Ok - -std::slice s(0, 50, 2); - -v[s] *= 2.0; // ERROR -}</pre> -</blockquote> -<p>I can't understand the intent of that omission. It makes the -valarray library less intuitive and less useful.</p> - - -<p><b>Rationale:</b></p> -<p>Although perhaps an unfortunate -design decision, the omission is not a defect in the current -standard. A future standard may wish to add the missing -operators.</p> - - - - -<hr> -<h3><a name="190"></a>190. min() and max() functions should be std::binary_functions</h3> -<p><b>Section:</b> 25.4.7 [alg.min.max] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Mark Rintoul <b>Opened:</b> 1999-08-26 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.min.max">issues</a> in [alg.min.max].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Both std::min and std::max are defined as template functions. This -is very different than the definition of std::plus (and similar -structs) which are defined as function objects which inherit -std::binary_function.<br/> -<br/> - This lack of inheritance leaves std::min and std::max somewhat useless in standard library algorithms which require -a function object that inherits std::binary_function.</p> - -<p><i>[ -post Bellevue: Alisdair requested to re-Open. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -C++0x has lambdas to address this problem now. -</p> -<p> -Moved to NAD. -</p> -</blockquote> - - - -<p><b>Rationale:</b></p> -<p>Although perhaps an unfortunate design decision, the omission is not a defect -in the current standard. A future standard may wish to consider additional -function objects.</p> - - - - -<hr> -<h3><a name="191"></a>191. Unclear complexity for algorithms such as binary search</h3> -<p><b>Section:</b> 25.4.3 [alg.binary.search] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 1999-10-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.binary.search">issues</a> in [alg.binary.search].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The complexity of binary_search() is stated as "At most -log(last-first) + 2 comparisons", which seems to say that the -algorithm has logarithmic complexity. However, this algorithms is -defined for forward iterators. And for forward iterators, the need to -step element-by-element results into linear complexity. But such a -statement is missing in the standard. The same applies to -lower_bound(), upper_bound(), and equal_range(). <br/> -<br/> -However, strictly speaking the standard contains no bug here. So this -might considered to be a clarification or improvement. -</p> - - -<p><b>Rationale:</b></p> -<p>The complexity is expressed in terms of comparisons, and that -complexity can be met even if the number of iterators accessed is -linear. Paragraph 1 already says exactly what happens to -iterators.</p> - - - - -<hr> -<h3><a name="192"></a>192. a.insert(p,t) is inefficient and overconstrained</h3> -<p><b>Section:</b> 23.2.4 [associative.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Ed Brey <b>Opened:</b> 1999-06-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#233">233</a></p> -<p><b>Discussion:</b></p> -<p>As defined in 23.1.2, paragraph 7 (table 69), a.insert(p,t) suffers from -several problems:</p> -<table border="1" cellpadding="5"> - <tr> - <td><b>expression</b></td> - <td><b>return type</b></td> - <td><b>pre/post-condition</b></td> - <td><b>complexity</b></td> - </tr> - <tr> - <td><tt>a.insert(p,t)</tt></td> - <td><tt>iterator</tt></td> - <td>inserts t if and only if there is no element with key equivalent to the key of - t in containers with unique keys; always inserts t in containers with equivalent - keys. always returns the iterator pointing to the element with key equivalent to - the key of t . iterator p is a hint pointing to where the insert should start to search.</td> - <td>logarithmic in general, but amortized constant if t is inserted right after p .</td> - </tr> -</table> -<p>1. For a container with unique keys, only logarithmic complexity is -guaranteed if no element is inserted, even though constant complexity is always -possible if p points to an element equivalent to t.</p> -<p>2. For a container with equivalent keys, the amortized constant complexity -guarantee is only useful if no key equivalent to t exists in the container. -Otherwise, the insertion could occur in one of multiple locations, at least one -of which would not be right after p.</p> -<p>3. By guaranteeing amortized constant complexity only when t is inserted -after p, it is impossible to guarantee constant complexity if t is inserted at -the beginning of the container. Such a problem would not exist if amortized -constant complexity was guaranteed if t is inserted before p, since there is -always some p immediately before which an insert can take place.</p> -<p>4. For a container with equivalent keys, p does not allow specification of -where to insert the element, but rather only acts as a hint for improving -performance. This negates the added functionality that p would provide if it -specified where within a sequence of equivalent keys the insertion should occur. -Specifying the insert location provides more control to the user, while -providing no disadvantage to the container implementation.</p> - - -<p><b>Proposed resolution:</b></p> -<p>In 23.2.4 [associative.reqmts] paragraph 7, replace the row in table 69 -for a.insert(p,t) with the following two rows:</p> -<table border="1" cellpadding="5"> - <tr> - <td><b>expression</b></td> - <td><b>return type</b></td> - <td><b>pre/post-condition</b></td> - <td><b>complexity</b></td> - </tr> - <tr> - <td><tt>a_uniq.insert(p,t)</tt></td> - <td><tt>iterator</tt></td> - <td>inserts t if and only if there is no element with key equivalent to the - key of t. returns the iterator pointing to the element with key equivalent - to the key of t.</td> - <td>logarithmic in general, but amortized constant if t is inserted right - before p or p points to an element with key equivalent to t.</td> - </tr> - <tr> - <td><tt>a_eq.insert(p,t)</tt></td> - <td><tt>iterator</tt></td> - <td>inserts t and returns the iterator pointing to the newly inserted - element. t is inserted right before p if doing so preserves the container - ordering.</td> - <td>logarithmic in general, but amortized constant if t is inserted right - before p.</td> - </tr> -</table> - - - -<p><b>Rationale:</b></p> -<p>Too big a change. Furthermore, implementors report checking -both before p and after p, and don't want to change this behavior.</p> - - - - - -<hr> -<h3><a name="194"></a>194. rdbuf() functions poorly specified</h3> -<p><b>Section:</b> 27.5.5 [ios] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Steve Clamage <b>Opened:</b> 1999-09-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>In classic iostreams, base class ios had an rdbuf function that returned a -pointer to the associated streambuf. Each derived class had its own rdbuf -function that returned a pointer of a type reflecting the actual type derived -from streambuf. Because in ARM C++, virtual function overrides had to have the -same return type, rdbuf could not be virtual.</p> -<p>In standard iostreams, we retain the non-virtual rdbuf function design, and -in addition have an overloaded rdbuf function that sets the buffer pointer. -There is no need for the second function to be virtual nor to be implemented in -derived classes.</p> -<p>Minor question: Was there a specific reason not to make the original rdbuf -function virtual?</p> -<p>Major problem: Friendly compilers warn about functions in derived classes -that hide base-class overloads. Any standard implementation of iostreams will -result in such a warning on each of the iostream classes, because of the -ill-considered decision to overload rdbuf only in a base class.</p> -<p>In addition, users of the second rdbuf function must use explicit -qualification or a cast to call it from derived classes. An explicit -qualification or cast to basic_ios would prevent access to any later overriding -version if there was one.</p> -<p>What I'd like to do in an implementation is add a using- declaration for the -second rdbuf function in each derived class. It would eliminate warnings about -hiding functions, and would enable access without using explicit qualification. -Such a change I don't think would change the behavior of any valid program, but -would allow invalid programs to compile:</p> -<blockquote> - <pre> filebuf mybuf; - fstream f; - f.rdbuf(mybuf); // should be an error, no visible rdbuf</pre> -</blockquote> -<p>I'd like to suggest this problem as a defect, with the proposed resolution to -require the equivalent of a using-declaration for the rdbuf function that is not -replaced in a later derived class. We could discuss whether replacing the -function should be allowed.</p> - - -<p><b>Rationale:</b></p> -<p>For historical reasons, the standard is correct as written. There is a subtle difference between the base -class <tt> rdbuf()</tt> and derived class <tt>rdbuf()</tt>. The derived -class <tt> rdbuf()</tt> always returns the original streambuf, whereas the base class -<tt> rdbuf()</tt> will return the "current streambuf" if that has been changed by the variant you mention.</p> - -<p>Permission is not required to add such an extension. See -17.6.5.5 [member.functions].</p> - - - - -<hr> -<h3><a name="196"></a>196. Placement new example has alignment problems</h3> -<p><b>Section:</b> 18.6.1.3 [new.delete.placement] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Herb Sutter <b>Opened:</b> 1998-12-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#new.delete.placement">issues</a> in [new.delete.placement].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#114">114</a></p> -<p><b>Discussion:</b></p> -<p>The example in 18.6.1.3 [new.delete.placement] paragraph 4 reads: </p> - -<blockquote> - -<p>[Example: This can be useful for constructing an object at a known address:<br/> -<br/> -<tt> char place[sizeof(Something)];<br/> - Something* p = new (place) Something();<br/> -<br/> -</tt>end example] </p> - -</blockquote> - -<p>This example has potential alignment problems. </p> - - -<p><b>Rationale:</b></p> - - - - - -<hr> -<h3><a name="197"></a>197. max_size() underspecified</h3> -<p><b>Section:</b> 17.6.3.5 [allocator.requirements], 23.2 [container.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Andy Sawyer <b>Opened:</b> 1999-10-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#allocator.requirements">active issues</a> in [allocator.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#allocator.requirements">issues</a> in [allocator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Must the value returned by max_size() be unchanged from call to call? </p> - -<p>Must the value returned from max_size() be meaningful? </p> - -<p>Possible meanings identified in lib-6827: </p> - -<p>1) The largest container the implementation can support given "best -case" conditions - i.e. assume the run-time platform is "configured to -the max", and no overhead from the program itself. This may possibly -be determined at the point the library is written, but certainly no -later than compile time.<br/> -<br/> -2) The largest container the program could create, given "best case" -conditions - i.e. same platform assumptions as (1), but take into -account any overhead for executing the program itself. (or, roughly -"storage=storage-sizeof(program)"). This does NOT include any resource -allocated by the program. This may (or may not) be determinable at -compile time.<br/> -<br/> -3) The largest container the current execution of the program could -create, given knowledge of the actual run-time platform, but again, -not taking into account any currently allocated resource. This is -probably best determined at program start-up.<br/> -<br/> -4) The largest container the current execution program could create at -the point max_size() is called (or more correctly at the point -max_size() returns :-), given it's current environment (i.e. taking -into account the actual currently available resources). This, -obviously, has to be determined dynamically each time max_size() is -called. </p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>max_size() isn't useful for very many things, and the existing - wording is sufficiently clear for the few cases that max_size() can - be used for. None of the attempts to change the existing wording - were an improvement.</p> - -<p>It is clear to the LWG that the value returned by max_size() can't - change from call to call.</p> - - - - - - -<hr> -<h3><a name="203"></a>203. basic_istream::sentry::sentry() is uninstantiable with ctype<user-defined type></h3> -<p><b>Section:</b> 27.7.2.1.3 [istream::sentry] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt McClure and Dietmar Kühl <b>Opened:</b> 2000-01-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#istream::sentry">issues</a> in [istream::sentry].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>27.6.1.1.2 Paragraph 4 states:</p> -<blockquote> - <p>To decide if the character c is a whitespace character, the constructor - performs ''as if'' it executes the following code fragment: </p> - <pre>const ctype<charT>& ctype = use_facet<ctype<charT> >(is.getloc()); -if (ctype.is(ctype.space,c)!=0) -// c is a whitespace character.</pre> -</blockquote> - -<p> But Table 51 in 22.1.1.1.1 only requires an implementation to -provide specializations for ctype<char> and -ctype<wchar_t>. If sentry's constructor is implemented using -ctype, it will be uninstantiable for a user-defined character type -charT, unless the implementation has provided non-working (since it -would be impossible to define a correct ctype<charT> specialization -for an arbitrary charT) definitions of ctype's virtual member -functions.</p> - -<p> -It seems the intent the standard is that sentry should behave, in -every respect, not just during execution, as if it were implemented -using ctype, with the burden of providing a ctype specialization -falling on the user. But as it is written, nothing requires the -translation of sentry's constructor to behave as if it used the above -code, and it would seem therefore, that sentry's constructor should be -instantiable for all character types. -</p> - -<p> -Note: If I have misinterpreted the intent of the standard with -respect to sentry's constructor's instantiability, then a note should -be added to the following effect: -</p> - -<blockquote><p> -An implementation is forbidden from using the above code if it renders -the constructor uninstantiable for an otherwise valid character -type. -</p></blockquote> - -<p>In any event, some clarification is needed.</p> - - - -<p><b>Rationale:</b></p> -<p>It is possible but not easy to instantiate on types other than char -or wchar_t; many things have to be done first. That is by intention -and is not a defect.</p> - - - - -<hr> -<h3><a name="204"></a>204. distance(first, last) when "last" is before "first"</h3> -<p><b>Section:</b> 24.4.4 [iterator.operations] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Rintala Matti <b>Opened:</b> 2000-01-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iterator.operations">issues</a> in [iterator.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Section 24.3.4 describes the function distance(first, last) (where first and -last are iterators) which calculates "the number of increments or -decrements needed to get from 'first' to 'last'".</p> -<p>The function should work for forward, bidirectional and random access -iterators, and there is a requirement 24.3.4.5 which states that "'last' -must be reachable from 'first'".</p> -<p>With random access iterators the function is easy to implement as "last -- first".</p> -<p>With forward iterators it's clear that 'first' must point to a place before -'last', because otherwise 'last' would not be reachable from 'first'.</p> -<p>But what about bidirectional iterators? There 'last' is reachable from -'first' with the -- operator even if 'last' points to an earlier position than -'first'. However, I cannot see how the distance() function could be implemented -if the implementation does not know which of the iterators points to an earlier -position (you cannot use ++ or -- on either iterator if you don't know which -direction is the "safe way to travel").</p> -<p>The paragraph 24.3.4.1 states that "for ... bidirectional iterators they -use ++ to provide linear time implementations". However, the ++ operator is -not mentioned in the reachability requirement. Furthermore 24.3.4.4 explicitly -mentions that distance() returns the number of increments _or decrements_, -suggesting that it could return a negative number also for bidirectional -iterators when 'last' points to a position before 'first'.</p> -<p>Is a further requirement is needed to state that for forward and -bidirectional iterators "'last' must be reachable from 'first' using the ++ -operator". Maybe this requirement might also apply to random access -iterators so that distance() would work the same way for every iterator -category?</p> - - -<p><b>Rationale:</b></p> -<p>"Reachable" is defined in the standard in X [iterator.concepts] paragraph 6. -The definition is only in terms of operator++(). The LWG sees no defect in -the standard.</p> - - - - -<hr> -<h3><a name="205"></a>205. numeric_limits unclear on how to determine floating point types</h3> -<p><b>Section:</b> 18.3.2.4 [numeric.limits.members] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Steve Cleary <b>Opened:</b> 2000-01-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#numeric.limits.members">issues</a> in [numeric.limits.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>In several places in 18.3.2.4 [numeric.limits.members], a member is -described as "Meaningful for all floating point types." -However, no clear method of determining a floating point type is -provided.</p> - -<p>In 18.3.2.7 [numeric.special], paragraph 1 states ". . . (for -example, epsilon() is only meaningful if is_integer is -false). . ." which suggests that a type is a floating point type -if is_specialized is true and is_integer is false; however, this is -unclear.</p> - -<p>When clarifying this, please keep in mind this need of users: what -exactly is the definition of floating point? Would a fixed point or -rational representation be considered one? I guess my statement here -is that there could also be types that are neither integer or -(strictly) floating point.</p> - - -<p><b>Rationale:</b></p> -<p>It is up to the implementor of a user define type to decide if it is a -floating point type.</p> - - - - -<hr> -<h3><a name="207"></a>207. ctype<char> members return clause incomplete</h3> -<p><b>Section:</b> 22.4.1.3.2 [facet.ctype.char.members] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Robert Klarer <b>Opened:</b> 1999-11-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#facet.ctype.char.members">issues</a> in [facet.ctype.char.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#153">153</a></p> -<p><b>Discussion:</b></p> -<p> -The <tt>widen</tt> and <tt>narrow</tt> member functions are described -in 22.2.1.3.2, paragraphs 9-11. In each case we have two overloaded -signatures followed by a <b>Returns</b> clause. The <b>Returns</b> -clause only describes one of the overloads. -</p> - - -<p><b>Proposed resolution:</b></p> -<p>Change the returns clause in 22.4.1.3.2 [facet.ctype.char.members] -paragraph 10 from:</p> -<p> Returns: do_widen(low, high, to).</p> - -<p>to:</p> -<p> Returns: do_widen(c) or do_widen(low, high, to), -respectively.</p> - -<p>Change the returns clause in 22.4.1.3.2 [facet.ctype.char.members] paragraph 11 -from:</p> -<p> Returns: do_narrow(low, high, to).</p> - -<p>to:</p> -<p> Returns: do_narrow(c) or do_narrow(low, high, to), -respectively.</p> - - -<p><b>Rationale:</b></p> -<p>Subsumed by issue <a href="lwg-defects.html#153">153</a>, which addresses the same -paragraphs.</p> - - - - - - -<hr> -<h3><a name="213"></a>213. Math function overloads ambiguous</h3> -<p><b>Section:</b> 26.8 [c.math] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nico Josuttis <b>Opened:</b> 2000-02-26 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.math">active issues</a> in [c.math].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Due to the additional overloaded versions of numeric functions for -float and long double according to Section 26.5, calls such as int x; -std::pow (x, 4) are ambiguous now in a standard conforming -implementation. Current implementations solve this problem very -different (overload for all types, don't overload for float and long -double, use preprocessor, follow the standard and get -ambiguities).</p> <p>This behavior should be standardized or at least -identified as implementation defined.</p> - - -<p><b>Rationale:</b></p> -<p>These math issues are an -understood and accepted consequence of the design. They have -been discussed several times in the past. Users must write casts -or write floating point expressions as arguments.</p> - - - - -<hr> -<h3><a name="215"></a>215. Can a map's key_type be const?</h3> -<p><b>Section:</b> 23.2.4 [associative.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Judy Ward <b>Opened:</b> 2000-02-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>A user noticed that this doesn't compile with the Rogue Wave library because -the rb_tree class declares a key_allocator, and allocator<const int> is -not legal, I think:</p> -<blockquote> - <pre>map < const int, ... > // legal?</pre> -</blockquote> -<p>which made me wonder whether it is legal for a map's key_type to be const. In -email from Matt Austern he said:</p> -<blockquote> -<p>I'm not sure whether it's legal to declare a map with a const key type. I -hadn't thought about that question until a couple weeks ago. My intuitive -feeling is that it ought not to be allowed, and that the standard ought to say -so. It does turn out to work in SGI's library, though, and someone in the -compiler group even used it. Perhaps this deserves to be written up as an issue -too.</p> -</blockquote> - - -<p><b>Rationale:</b></p> -<p>The "key is assignable" requirement from table 69 in -23.2.4 [associative.reqmts] already implies the key cannot be const.</p> - - - - -<hr> -<h3><a name="216"></a>216. setbase manipulator description flawed</h3> -<p><b>Section:</b> 27.7.4 [std.manip] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Hyman Rosen <b>Opened:</b> 2000-02-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#std.manip">issues</a> in [std.manip].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#193">193</a></p> -<p><b>Discussion:</b></p> -<p>27.7.4 [std.manip] paragraph 5 says:</p> -<blockquote> -<pre>smanip setbase(int base);</pre> -<p> Returns: An object s of unspecified type such that if out is an -(instance of) basic_ostream then the expression out<<s behaves -as if f(s) were called, in is an (instance of) basic_istream then the -expression in>>s behaves as if f(s) were called. Where f can be -defined as:</p> -<pre>ios_base& f(ios_base& str, int base) -{ - // set basefield - str.setf(n == 8 ? ios_base::oct : - n == 10 ? ios_base::dec : - n == 16 ? ios_base::hex : - ios_base::fmtflags(0), ios_base::basefield); - return str; -}</pre> -</blockquote> -<p>There are two problems here. First, f takes two parameters, so the -description needs to say that out<<s and in>>s behave as if f(s,base) -had been called. Second, f is has a parameter named base, but is written as if -the parameter was named n.</p> -<p>Actually, there's a third problem. The paragraph has grammatical errors. -There needs to be an "and" after the first comma, and the "Where -f" sentence fragment needs to be merged into its preceding sentence. You -may also want to format the function a little better. The formatting above is -more-or-less what the Standard contains.</p> - - -<p><b>Rationale:</b></p> -<p>The resolution of this defect is subsumed by the proposed resolution for -issue <a href="lwg-defects.html#193">193</a>.</p> - -<p><i>[Tokyo: The LWG agrees that this is a defect and notes that it -occurs additional places in the section, all requiring fixes.]</i></p> - - - - - - - - -<hr> -<h3><a name="218"></a>218. Algorithms do not use binary predicate objects for default comparisons</h3> -<p><b>Section:</b> 25.4 [alg.sorting] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pablo Halpern <b>Opened:</b> 2000-03-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.sorting">issues</a> in [alg.sorting].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Many of the algorithms take an argument, pred, of template parameter type -BinaryPredicate or an argument comp of template parameter type Compare. These -algorithms usually have an overloaded version that does not take the predicate -argument. In these cases pred is usually replaced by the use of operator== and -comp is replaced by the use of operator<.</p> -<p>This use of hard-coded operators is inconsistent with other parts of the -library, particularly the containers library, where equality is established -using equal_to<> and ordering is established using less<>. Worse, -the use of operator<, would cause the following innocent-looking code to have -undefined behavior:</p> -<blockquote> - <pre>vector<string*> vec; -sort(vec.begin(), vec.end());</pre> -</blockquote> -<p>The use of operator< is not defined for pointers to unrelated objects. If -std::sort used less<> to compare elements, then the above code would be -well-defined, since less<> is explicitly specialized to produce a total -ordering of pointers.</p> - - -<p><b>Rationale:</b></p> -<p>This use of operator== and operator< was a very deliberate, conscious, and -explicitly made design decision; these operators are often more efficient. The -predicate forms are available for users who don't want to rely on operator== and -operator<.</p> - - - - -<hr> -<h3><a name="219"></a>219. <tt>find</tt> algorithm missing version that takes a binary predicate argument</h3> -<p><b>Section:</b> 25.2.5 [alg.find] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pablo Halpern <b>Opened:</b> 2000-03-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.find">issues</a> in [alg.find].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The find function always searches for a value using <tt>operator==</tt> to compare the -value argument to each element in the input iterator range. This is inconsistent -with other find-related functions such as <tt>find_end</tt> and <tt>find_first_of</tt>, which -allow the caller to specify a binary predicate object to be used for determining -equality. The fact that this can be accomplished using a combination of <tt>find_if</tt> -and <tt>bind_1st</tt> or <tt>bind_2nd</tt> does not negate the desirability of a consistent, -simple, alternative interface to <tt>find</tt>.</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Reopened by Alisdair. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -The same thing can be achieved using <tt>find_if</tt> (as noted in the issue). -</p> -<p> -Moved to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<blockquote> -<p>In section 25.2.5 [alg.find], add a second prototype for find -(between the existing prototype and the prototype for find_if), as -follows:</p> -<pre> template<class InputIterator, class T, class BinaryPredicate> - InputIterator find(InputIterator first, InputIterator last, - const T& value, BinaryPredicate bin_pred);</pre> -<p>Change the description of the return from:</p> -<blockquote> - <p>Returns: The first iterator <tt>i</tt> in the range <tt>[first, last)</tt> for which the following corresponding - conditions hold: <tt>*i == value</tt>, <tt>pred(*i) != false</tt>. Returns <tt>last</tt> if no such iterator is found.</p> -</blockquote> -<p> to:</p> -<blockquote> - <p>Returns: The first iterator <tt>i</tt> in the range <tt>[first, last)</tt> for which the following - corresponding condition holds: <tt>*i == value</tt>, <tt>bin_pred(*i,value) != false</tt>, <tt>pred(*) - != false</tt>. Return <tt>last</tt> if no such iterator is found.</p> -</blockquote> -</blockquote> - - -<p><b>Rationale:</b></p> -<p>This is request for a pure extension, so it is not a defect in the -current standard. As the submitter pointed out, "this can -be accomplished using a combination of <tt>find_if</tt> and <tt>bind_1st</tt> or -<tt>bind_2nd</tt>".</p> - - - - -<hr> -<h3><a name="236"></a>236. ctype<char>::is() member modifies facet</h3> -<p><b>Section:</b> 22.4.1.3.2 [facet.ctype.char.members] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Dietmar Kühl <b>Opened:</b> 2000-04-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#facet.ctype.char.members">issues</a> in [facet.ctype.char.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#28">28</a></p> -<p><b>Discussion:</b></p> -<p>The description of the <tt>is()</tt> member in paragraph 4 of 22.4.1.3.2 [facet.ctype.char.members] is broken: According to this description, the -second form of the <tt>is()</tt> method modifies the masks in the -<tt>ctype</tt> object. The correct semantics if, of course, to obtain -an array of masks. The corresponding method in the general case, -ie. the <tt>do_is()</tt> method as described in 22.4.1.1.2 [locale.ctype.virtuals] paragraph 1 does the right thing.</p> - - -<p><b>Proposed resolution:</b></p> - <p>Change paragraph 4 from</p> - <blockquote><p> - The second form, for all *p in the range [low, high), assigns - vec[p-low] to table()[(unsigned char)*p]. - </p></blockquote> - <p>to become</p> - <blockquote><p> - The second form, for all *p in the range [low, high), assigns - table()[(unsigned char)*p] to vec[p-low]. - </p></blockquote> - - -<p><b>Rationale:</b></p> - - - - - -<hr> -<h3><a name="244"></a>244. Must <tt>find</tt>'s third argument be CopyConstructible?</h3> -<p><b>Section:</b> 25.2.5 [alg.find] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Andrew Koenig <b>Opened:</b> 2000-05-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.find">issues</a> in [alg.find].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Is the following implementation of <tt>find</tt> acceptable?</p> - -<pre> - template<class Iter, class X> - Iter find(Iter begin, Iter end, const X& x) - { - X x1 = x; // this is the crucial statement - while (begin != end && *begin != x1) - ++begin; - return begin; - } -</pre> - -<p>If the answer is yes, then it is implementation-dependent as to -whether the following fragment is well formed:</p> - -<pre> - vector<string> v; - - find(v.begin(), v.end(), "foo"); -</pre> - -<p>At issue is whether there is a requirement that the third argument -of find be CopyConstructible. There may be no problem here, but -analysis is necessary.</p> - - -<p><b>Rationale:</b></p> -<p>There is no indication in the standard that find's third argument -is required to be Copy Constructible. The LWG believes that no such -requirement was intended. As noted above, there are times when a user -might reasonably pass an argument that is not Copy Constructible.</p> - - - - -<hr> -<h3><a name="245"></a>245. Which operations on <tt>istream_iterator</tt> trigger input operations?</h3> -<p><b>Section:</b> 24.6.1 [istream.iterator] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Andrew Koenig <b>Opened:</b> 2000-05-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#istream.iterator">issues</a> in [istream.iterator].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>I do not think the standard specifies what operation(s) on istream -iterators trigger input operations. So, for example:</p> - -<pre> - istream_iterator<int> i(cin); - - int n = *i++; -</pre> - -<p>I do not think it is specified how many integers have been read -from cin. The number must be at least 1, of course, but can it be 2? -More?</p> - - -<p><b>Rationale:</b></p> -<p>The standard is clear as written: the stream is read every time -operator++ is called, and it is also read either when the iterator is -constructed or when operator* is called for the first time. In the -example above, exactly two integers are read from cin.</p> - -<p>There may be a problem with the interaction between istream_iterator -and some STL algorithms, such as find. There are no guarantees about -how many times find may invoke operator++.</p> - - - - -<hr> -<h3><a name="246"></a>246. <tt>a.insert(p,t)</tt> is incorrectly specified</h3> -<p><b>Section:</b> 23.2.4 [associative.reqmts] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Mark Rodgers <b>Opened:</b> 2000-05-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#233">233</a></p> -<p><b>Discussion:</b></p> -<p>Closed issue 192 raised several problems with the specification of -this function, but was rejected as Not A Defect because it was too big -a change with unacceptable impacts on existing implementations. -However, issues remain that could be addressed with a smaller change -and with little or no consequent impact.</p> - -<ol> - <li><p> The specification is inconsistent with the original - proposal and with several implementations.</p> - - <p>The initial implementation by Hewlett Packard only ever looked - immediately <i>before</i> p, and I do not believe there was any - intention to standardize anything other than this behavior. - Consequently, current implementations by several leading - implementors also look immediately before p, and will only insert - after p in logarithmic time. I am only aware of one implementation - that does actually look after p, and it looks before p as well. It - is therefore doubtful that existing code would be relying on the - behavior defined in the standard, and it would seem that fixing - this defect as proposed below would standardize existing - practice.</p></li> - - <li><p> - The specification is inconsistent with insertion for sequence - containers.</p> - - <p>This is difficult and confusing to teach to newcomers. All - insert operations that specify an iterator as an insertion location - should have a consistent meaning for the location represented by - that iterator.</p></li> - - <li><p> As specified, there is no way to hint that the insertion - should occur at the beginning of the container, and the way to hint - that it should occur at the end is long winded and unnatural.</p> - - <p>For a container containing n elements, there are n+1 possible - insertion locations and n+1 valid iterators. For there to be a - one-to-one mapping between iterators and insertion locations, the - iterator must represent an insertion location immediately before - the iterator.</p></li> - - <li><p> When appending sorted ranges using insert_iterators, - insertions are guaranteed to be sub-optimal.</p> - - <p>In such a situation, the optimum location for insertion is - always immediately after the element previously inserted. The - mechanics of the insert iterator guarantee that it will try and - insert after the element after that, which will never be correct. - However, if the container first tried to insert before the hint, - all insertions would be performed in amortized constant - time.</p></li> -</ol> - - -<p><b>Proposed resolution:</b></p> -<p>In 23.1.2 [lib.associative.reqmts] paragraph 7, table 69, make -the following changes in the row for a.insert(p,t):</p> - -<p><i>assertion/note pre/post condition:</i> -<br/>Change the last sentence from</p> - <blockquote><p> - "iterator p is a hint pointing to where the insert should - start to search." - </p></blockquote> -<p>to</p> - <blockquote><p> - "iterator p is a hint indicating that immediately before p - may be a correct location where the insertion could occur." - </p></blockquote> - -<p><i>complexity:</i><br/> -Change the words "right after" to "immediately before".</p> - - -<p><b>Rationale:</b></p> - - - - - -<hr> -<h3><a name="249"></a>249. Return Type of <tt>auto_ptr::operator=</tt></h3> -<p><b>Section:</b> X [auto.ptr] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Joseph Gottman <b>Opened:</b> 2000-06-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#auto.ptr">issues</a> in [auto.ptr].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>According to section 20.4.5, the function -<tt>auto_ptr::operator=()</tt> returns a reference to an auto_ptr. -The reason that <tt>operator=()</tt> usually returns a reference is to -facilitate code like</p> - -<pre> - int x,y,z; - x = y = z = 1; -</pre> - -<p>However, given analogous code for <tt>auto_ptr</tt>s,</p> -<pre> - auto_ptr<int> x, y, z; - z.reset(new int(1)); - x = y = z; -</pre> - -<p>the result would be that <tt>z</tt> and <tt>y</tt> would both be set to -NULL, instead of all the <tt>auto_ptr</tt>s being set to the same value. -This makes such cascading assignments useless and counterintuitive for -<tt>auto_ptr</tt>s.</p> - - -<p><b>Proposed resolution:</b></p> -<p>Change <tt>auto_ptr::operator=()</tt> to return <tt>void</tt> instead -of an <tt>auto_ptr</tt> reference.</p> - - -<p><b>Rationale:</b></p> -<p>The return value has uses other than cascaded assignments: a user can -call an auto_ptr member function, pass the auto_ptr to a -function, etc. Removing the return value could break working user -code.</p> - - - - -<hr> -<h3><a name="257"></a>257. STL functional object and iterator inheritance.</h3> -<p><b>Section:</b> X [depr.base], 24.4.2 [iterator.basic] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Robert Dick <b>Opened:</b> 2000-08-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#depr.base">issues</a> in [depr.base].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -According to the November 1997 Draft Standard, the results of deleting an -object of a derived class through a pointer to an object of its base class are -undefined if the base class has a non-virtual destructor. Therefore, it is -potentially dangerous to publicly inherit from such base classes. -</p> - -<p>Defect: -<br/> -The STL design encourages users to publicly inherit from a number of classes -which do nothing but specify interfaces, and which contain non-virtual -destructors. -</p> - -<p>Attribution: -<br/> -Wil Evers and William E. Kempf suggested this modification for functional -objects. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -When a base class in the standard library is useful only as an interface -specifier, i.e., when an object of the class will never be directly -instantiated, specify that the class contains a protected destructor. This -will prevent deletion through a pointer to the base class without performance, -or space penalties (on any implementation I'm aware of). -</p> - -<p> -As an example, replace... -</p> - -<pre> - template <class Arg, class Result> - struct unary_function { - typedef Arg argument_type; - typedef Result result_type; - }; -</pre> - -<p> -... with... -</p> - -<pre> - template <class Arg, class Result> - struct unary_function { - typedef Arg argument_type; - typedef Result result_type; - protected: - ~unary_function() {} - }; -</pre> - -<p> -Affected definitions: -<br/> - 20.3.1 [lib.function.objects] -- unary_function, binary_function - <br/> - 24.3.2 [lib.iterator.basic] -- iterator -</p> - - -<p><b>Rationale:</b></p> -<p> -The standard is clear as written; this is a request for change, not a -defect in the strict sense. The LWG had several different objections -to the proposed change. One is that it would prevent users from -creating objects of type <tt>unary_function</tt> and -<tt>binary_function</tt>. Doing so can sometimes be legitimate, if users -want to pass temporaries as traits or tag types in generic code. -</p> - - - - - -<hr> -<h3><a name="267"></a>267. interaction of strstreambuf::overflow() and seekoff()</h3> -<p><b>Section:</b> D.7.1.3 [depr.strstreambuf.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2000-10-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#depr.strstreambuf.virtuals">issues</a> in [depr.strstreambuf.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -It appears that the interaction of the strstreambuf members overflow() -and seekoff() can lead to undefined behavior in cases where defined -behavior could reasonably be expected. The following program -demonstrates this behavior: -</p> - -<pre> - #include <strstream> - - int main () - { - std::strstreambuf sb; - sb.sputc ('c'); - - sb.pubseekoff (-1, std::ios::end, std::ios::in); - return !('c' == sb.sgetc ()); - } -</pre> - -<p> -D.7.1.1, p1 initializes strstreambuf with a call to basic_streambuf<>(), -which in turn sets all pointers to 0 in 27.5.2.1, p1. -</p> - -<p> -27.5.2.2.5, p1 says that basic_streambuf<>::sputc(c) calls -overflow(traits::to_int_type(c)) if a write position isn't available (it -isn't due to the above). -</p> - -<p> -D.7.1.3, p3 says that strstreambuf::overflow(off, ..., ios::in) makes at -least one write position available (i.e., it allows the function to make -any positive number of write positions available). -</p> - -<p> -D.7.1.3, p13 computes newoff = seekhigh - eback(). In D.7.1, p4 we see -seekhigh = epptr() ? epptr() : egptr(), or seekhigh = epptr() in this -case. newoff is then epptr() - eback(). -</p> - -<p> -D.7.1.4, p14 sets gptr() so that gptr() == eback() + newoff + off, or -gptr() == epptr() + off holds. -</p> - -<p> -If strstreambuf::overflow() made exactly one write position available -then gptr() will be set to just before epptr(), and the program will -return 0. Buf if the function made more than one write position -available, epptr() and gptr() will both point past pptr() and the -behavior of the program is undefined. -</p> - - -<p><b>Proposed resolution:</b></p> - - - <p>Change the last sentence of D.7.1 [depr.strstreambuf] paragraph 4 from</p> - - <blockquote><p> - Otherwise, seeklow equals gbeg and seekhigh is either pend, if - pend is not a null pointer, or gend. - </p></blockquote> - - <p>to become</p> - - <blockquote><p> - Otherwise, seeklow equals gbeg and seekhigh is either gend if - 0 == pptr(), or pbase() + max where max is the maximum value of - pptr() - pbase() ever reached for this stream. - </p></blockquote> - -<p><i>[ - pre-Copenhagen: Dietmar provided wording for proposed resolution. -]</i></p> - - -<p><i>[ - post-Copenhagen: Fixed a typo: proposed resolution said to fix - 4.7.1, not D.7.1. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p>This is related to issue <a href="lwg-closed.html#65">65</a>: it's not clear what it -means to seek beyond the current area. Without resolving issue <a href="lwg-closed.html#65">65</a> we can't resolve this. As with issue <a href="lwg-closed.html#65">65</a>, -the library working group does not wish to invest time nailing down -corner cases in a deprecated feature.</p> - - - - - -<hr> -<h3><a name="269"></a>269. cstdarg and unnamed parameters</h3> -<p><b>Section:</b> 18.8 [support.exception] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> J. Stephen Adamczyk <b>Opened:</b> 2000-10-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#support.exception">issues</a> in [support.exception].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -One of our customers asks whether this is valid C++: -</p> - -<pre> - #include <cstdarg> - - void bar(const char *, va_list); - - void - foo(const char *file, const char *, ...) - { - va_list ap; - va_start(ap, file); - bar(file, ap); - va_end(ap); - } -</pre> - -<p> -The issue being whether it is valid to use cstdarg when the final -parameter before the "..." is unnamed. cstdarg is, as far -as I can tell, inherited verbatim from the C standard. and the -definition there (7.8.1.1 in the ISO C89 standard) refers to "the -identifier of the rightmost parameter". What happens when there -is no such identifier? -</p> - -<p> -My personal opinion is that this should be allowed, but some tweak -might be required in the C++ standard. -</p> - - -<p><b>Rationale:</b></p> -<p> -Not a defect, the C and C++ standards are clear. It is impossible to -use varargs if the parameter immediately before "..." has no -name, because that is the parameter that must be passed to va_start. -The example given above is broken, because va_start is being passed -the wrong parameter. -</p> - -<p> -There is no support for extending varargs to provide additional -functionality beyond what's currently there. For reasons of C/C++ -compatibility, it is especially important not to make gratuitous -changes in this part of the C++ standard. The C committee has already -been requested not to touch this part of the C standard unless -necessary. -</p> - - - - -<hr> -<h3><a name="277"></a>277. Normative encouragement in allocator requirements unclear</h3> -<p><b>Section:</b> 17.6.3.5 [allocator.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2000-11-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#allocator.requirements">active issues</a> in [allocator.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#allocator.requirements">issues</a> in [allocator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In 20.1.5, paragraph 5, the standard says that "Implementors are -encouraged to supply libraries that can accept allocators that -encapsulate more general memory models and that support non-equal -instances." This is intended as normative encouragement to -standard library implementors. However, it is possible to interpret -this sentence as applying to nonstandard third-party libraries. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In 20.1.5, paragraph 5, change "Implementors" to -"Implementors of the library described in this International -Standard". -</p> - - -<p><b>Rationale:</b></p> -<p>The LWG believes the normative encouragement is already -sufficiently clear, and that there are no important consequences -even if it is misunderstood.</p> - - - - - -<hr> -<h3><a name="279"></a>279. const and non-const iterators should have equivalent typedefs</h3> -<p><b>Section:</b> 23.2 [container.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Steve Cleary <b>Opened:</b> 2000-11-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#container.requirements">active issues</a> in [container.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#container.requirements">issues</a> in [container.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -This came from an email from Steve Cleary to Fergus in reference to -issue <a href="lwg-defects.html#179">179</a>. The library working group briefly discussed -this in Toronto and believes it should be a separate issue. -</p> - -<p> -Steve said: "We may want to state that the const/non-const iterators must have -the same difference type, size_type, and category." -</p> - -<p> -(Comment from Judy) -I'm not sure if the above sentence should be true for all -const and non-const iterators in a particular container, or if it means -the container's iterator can't be compared with the container's -const_iterator unless the above it true. I suspect the former. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In <b>Section:</b> 23.2 [container.requirements], -table 65, in the assertion/note pre/post condition for X::const_iterator, -add the following: -</p> - -<blockquote> -<p> -typeid(X::const_iterator::difference_type) == typeid(X::iterator::difference_type) -</p> - -<p> -typeid(X::const_iterator::size_type) == typeid(X::iterator::size_type) -</p> - -<p> -typeid(X::const_iterator::category) == typeid(X::iterator::category) -</p> -</blockquote> - - -<p><b>Rationale:</b></p> -<p>Going through the types one by one: Iterators don't have a -<tt>size_type</tt>. We already know that the difference types are -identical, because the container requirements already say that the -difference types of both X::iterator and X::const_iterator are both -X::difference_type. The standard does not require that X::iterator -and X::const_iterator have the same iterator category, but the LWG -does not see this as a defect: it's possible to imagine cases in which -it would be useful for the categories to be different.</p> - -<p>It may be desirable to require X::iterator and X::const_iterator to -have the same value type, but that is a new issue. (Issue <a href="lwg-defects.html#322">322</a>.)</p> - - - - - - -<hr> -<h3><a name="287"></a>287. conflicting ios_base fmtflags</h3> -<p><b>Section:</b> 27.5.3.2 [fmtflags.state] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Judy Ward <b>Opened:</b> 2000-12-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#fmtflags.state">issues</a> in [fmtflags.state].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The Effects clause for ios_base::setf(fmtflags fmtfl) says -"Sets fmtfl in flags()". What happens if the user first calls -ios_base::scientific and then calls ios_base::fixed or vice-versa? -This is an issue for all of the conflicting flags, i.e. ios_base::left -and ios_base::right or ios_base::dec, ios_base::hex and ios_base::oct. -</p> - -<p> -I see three possible solutions: -</p> - -<ol> -<li>Set ios_base::failbit whenever the user specifies a conflicting -flag with one previously explicitly set. If the constructor is -supposed to set ios_base::dec (see discussion below), then -the user setting hex or oct format after construction will not -set failbit. </li> -<li>The last call to setf "wins", i.e. it clears any conflicting -previous setting.</li> -<li>All the flags that the user specifies are set, but when actually -interpreting them, fixed always override scientific, right always -overrides left, dec overrides hex which overrides oct.</li> -</ol> - -<p> -Most existing implementations that I tried seem to conform to resolution #3, -except that when using the iomanip manipulator hex or oct then that always -overrides dec, but calling setf(ios_base::hex) doesn't. -</p> - -<p> -There is a sort of related issue, which is that although the ios_base -constructor says that each ios_base member has an indeterminate value -after construction, all the existing implementations I tried explicitly set -ios_base::dec. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p> -<tt>adjustfield</tt>, <tt>basefield</tt>, and <tt>floatfield</tt> -are each multi-bit fields. It is possible to set multiple bits within -each of those fields. (For example, <tt>dec</tt> and -<tt>oct</tt>). These fields are used by locale facets. The LWG -reviewed the way in which each of those three fields is used, and -believes that in each case the behavior is well defined for any -possible combination of bits. See for example Table 58, in 22.4.2.2.2 [facet.num.put.virtuals], noting the requirement in paragraph 6 of that -section. -</p> -<p> -Users are advised to use manipulators, or else use the two-argument -version of <tt>setf</tt>, to avoid unexpected behavior. -</p> - - - - - -<hr> -<h3><a name="289"></a>289. <cmath> requirements missing C float and long double versions</h3> -<p><b>Section:</b> 26.8 [c.math] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Judy Ward <b>Opened:</b> 2000-12-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.math">active issues</a> in [c.math].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> - In ISO/IEC 9899:1990 Programming Languages C we find the following - concerning <math.h>: -</p> - -<blockquote><p> - 7.13.4 Mathematics <math.h> - <br/> - The names of all existing functions declared in the <math.h> - header, suffixed with f or l, are reserved respectively for - corresponding functions with float and long double arguments - are return values. -</p></blockquote> - -<p> - For example, <tt>float sinf(float)</tt> - is reserved. -</p> - -<p> - In the C99 standard, <math.h> must contain declarations - for these functions. -</p> - -<p> -So, is it acceptable for an implementor to add these prototypes to the -C++ versions of the math headers? Are they required? -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add these Functions to Table 80, section 26.5 and to Table 99, -section C.2: -</p> - -<pre> - acosf asinf atanf atan2f ceilf cosf coshf - expf fabsf floorf fmodf frexpf ldexpf - logf log10f modff powf sinf sinhf sqrtf - tanf tanhf - acosl asinl atanl atan2l ceill cosl coshl - expl fabsl floorl fmodl frexpl ldexpl - logl log10l modfl powl sinl sinhl sqrtl - tanl tanhl -</pre> - -<p> -There should probably be a note saying that these functions -are optional and, if supplied, should match the description in -the 1999 version of the C standard. In the next round -of C++ standardization they can then become mandatory. -</p> - - -<p><b>Rationale:</b></p> -<p>The C90 standard, as amended, already permits (but does not -require) these functions, and the C++ standard incorporates the -C90 standard by reference. C99 is not an issue, because it is -never referred to by the C++ standard.</p> - - - - - -<hr> -<h3><a name="290"></a>290. Requirements to for_each and its function object</h3> -<p><b>Section:</b> 25.2.4 [alg.foreach] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Angelika Langer <b>Opened:</b> 2001-01-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.foreach">issues</a> in [alg.foreach].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The specification of the for_each algorithm does not have a -"Requires" section, which means that there are no -restrictions imposed on the function object whatsoever. In essence it -means that I can provide any function object with arbitrary side -effects and I can still expect a predictable result. In particular I -can expect that the function object is applied exactly last - first -times, which is promised in the "Complexity" section. -</p> - -<p>I don't see how any implementation can give such a guarantee -without imposing requirements on the function object. -</p> - -<p>Just as an example: consider a function object that removes -elements from the input sequence. In that case, what does the -complexity guarantee (applies f exactly last - first times) mean? -</p> - -<p>One can argue that this is obviously a nonsensical application and -a theoretical case, which unfortunately it isn't. I have seen -programmers shooting themselves in the foot this way, and they did not -understand that there are restrictions even if the description of the -algorithm does not say so. -</p> -<p><i>[Lillehammer: This is more general than for_each. We don't want - the function object in transform invalidiating iterators - either. There should be a note somewhere in clause 17 (17, not 25) - saying that user code operating on a range may not invalidate - iterators unless otherwise specified. Bill will provide wording.]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -Moved to NAD. -</p> -<p> -It was felt that the current description is adequate, and that there are -limits to what the standard can reasonably say to prohibit perverse uses -of the library. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - - -<hr> -<h3><a name="293"></a>293. Order of execution in transform algorithm</h3> -<p><b>Section:</b> 25.3.4 [alg.transform] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Angelika Langer <b>Opened:</b> 2001-01-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.transform">issues</a> in [alg.transform].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>This issue is related to issue 242. In case that the resolution -proposed for issue 242 is accepted, we have have the following -situation: The 4 numeric algorithms (accumulate and consorts) as well -as transform would allow a certain category of side effects. The -numeric algorithms specify that they invoke the functor "for -every iterator i in the range [first, last) in order". transform, -in contrast, would not give any guarantee regarding order of -invocation of the functor, which means that the functor can be invoked -in any arbitrary order. -</p> - -<p>Why would that be a problem? Consider an example: say the -transformator that is a simple enumerator ( or more generally -speaking, "is order-sensitive" ). Since a standard -compliant implementation of transform is free to invoke the enumerator -in no definite order, the result could be a garbled enumeration. -Strictly speaking this is not a problem, but it is certainly at odds -with the prevalent understanding of transform as an algorithms that -assigns "a new _corresponding_ value" to the output -elements. -</p> - -<p>All implementations that I know of invoke the transformator in -definite order, namely starting from first and proceeding to last - -1. Unless there is an optimization conceivable that takes advantage of -the indefinite order I would suggest to specify the order, because it -eliminate the uncertainty that users would otherwise have regarding -the order of execution of their potentially order-sensitive function -objects. -</p> - - -<p><b>Proposed resolution:</b></p> -<p>In section 25.2.3 - Transform [lib.alg.transform] change:</p> -<blockquote><p> --1- Effects: Assigns through every iterator i in the range [result, -result + (last1 - first1)) a new corresponding -value equal to op(*(first1 + (i - result)) or binary_op(*(first1 + -(i - result), *(first2 + (i - result))). -</p></blockquote> -<p>to:</p> -<blockquote><p> --1- Effects: Computes values by invoking the operation op or binary_op -for every iterator in the range [first1, last1) in order. Assigns through -every iterator i in the range [result, result + (last1 - first1)) a new -corresponding -value equal to op(*(first1 + (i - result)) or binary_op(*(first1 + -(i - result), *(first2 + (i - result))). -</p></blockquote> - - -<p><b>Rationale:</b></p> -<p>For Input Iterators an order is already guaranteed, because -only one order is possible. If a user who passes a Forward -Iterator to one of these algorithms really needs a specific -order of execution, it's possible to achieve that effect by -wrapping it in an Input Iterator adaptor.</p> - - - - - -<hr> -<h3><a name="299"></a>299. Incorrect return types for iterator dereference</h3> -<p><b>Section:</b> 24.2.6 [bidirectional.iterators], 24.2.7 [random.access.iterators] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> John Potter <b>Opened:</b> 2001-01-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#bidirectional.iterators">issues</a> in [bidirectional.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In section 24.2.6 [bidirectional.iterators], -Table 75 gives the return type of <tt>*r--</tt> as convertible to <tt>T</tt>. This is -not consistent with Table 74 which gives the return type of <tt>*r++</tt> as -<tt>T&</tt>. <tt>*r++ = t</tt> is valid while <tt>*r-- = t</tt> is invalid. -</p> - -<p> -In section 24.2.7 [random.access.iterators], -Table 76 gives the return type of <tt>a[n]</tt> as convertible to <tt>T</tt>. This is -not consistent with the semantics of <tt>*(a + n)</tt> which returns <tt>T&</tt> by -Table 74. <tt>*(a + n) = t</tt> is valid while <tt>a[n] = t</tt> is invalid. -</p> - -<p> -Discussion from the Copenhagen meeting: the first part is -uncontroversial. The second part, <tt>operator[]</tt> for Random Access -Iterators, requires more thought. There are reasonable arguments on -both sides. Return by value from <tt>operator[]</tt> enables some potentially -useful iterators, e.g. a random access "iota iterator" (a.k.a -"counting iterator" or "int iterator"). There isn't any obvious way -to do this with return-by-reference, since the reference would be to a -temporary. On the other hand, <tt>reverse_iterator</tt> takes an -arbitrary Random Access Iterator as template argument, and its -<tt>operator[]</tt> returns by reference. If we decided that the return type -in Table 76 was correct, we would have to change -<tt>reverse_iterator</tt>. This change would probably affect user -code. -</p> - -<p> -History: the contradiction between <tt>reverse_iterator</tt> and the -Random Access Iterator requirements has been present from an early -stage. In both the STL proposal adopted by the committee -(N0527==94-0140) and the STL technical report (HPL-95-11 (R.1), by -Stepanov and Lee), the Random Access Iterator requirements say that -<tt>operator[]</tt>'s return value is "convertible to <tt>T</tt>". In N0527 -reverse_iterator's <tt>operator[]</tt> returns by value, but in HPL-95-11 -(R.1), and in the STL implementation that HP released to the public, -reverse_iterator's <tt>operator[]</tt> returns by reference. In 1995, the -standard was amended to reflect the contents of HPL-95-11 (R.1). The -original intent for <tt>operator[]</tt> is unclear. -</p> - -<p> -In the long term it may be desirable to add more fine-grained -iterator requirements, so that access method and traversal strategy -can be decoupled. (See "Improved Iterator Categories and -Requirements", N1297 = 01-0011, by Jeremy Siek.) Any decisions -about issue 299 should keep this possibility in mind. -</p> - -<p>Further discussion: I propose a compromise between John Potter's -resolution, which requires <tt>T&</tt> as the return type of -<tt>a[n]</tt>, and the current wording, which requires convertible to -<tt>T</tt>. The compromise is to keep the convertible to <tt>T</tt> -for the return type of the expression <tt>a[n]</tt>, but to also add -<tt>a[n] = t</tt> as a valid expression. This compromise "saves" the -common case uses of random access iterators, while at the same time -allowing iterators such as counting iterator and caching file -iterators to remain random access iterators (iterators where the -lifetime of the object returned by <tt>operator*()</tt> is tied to the -lifetime of the iterator). -</p> - -<p> -Note that the compromise resolution necessitates a change to -<tt>reverse_iterator</tt>. It would need to use a proxy to support -<tt>a[n] = t</tt>. -</p> - -<p> -Note also there is one kind of mutable random access iterator that -will no longer meet the new requirements. Currently, iterators that -return an r-value from <tt>operator[]</tt> meet the requirements for a -mutable random access iterator, even though the expression <tt>a[n] = -t</tt> will only modify a temporary that goes away. With this proposed -resolution, <tt>a[n] = t</tt> will be required to have the same -operational semantics as <tt>*(a + n) = t</tt>. -</p> - -<p><i>[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]</i></p> - - -<p><i>[ -2009-09-18 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -Why can't we write through the reference returned from <tt>operator[]</tt> on a -random access iterator? -</p> - -<p> -Recommended solution: -</p> - -<p> -In table Table 104 — Random access iterator requirements, replace -</p> - -<blockquote><p> -<tt>a[n]</tt> : convertible to <del><tt>const T &</tt></del> -<ins><tt>T&</tt> if <tt>X</tt> is mutable, otherwise convertible to <tt>const T&</tt></ins> -</p></blockquote> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Leave Open. Alisdair to spearhead a paper on revivification. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -Solved by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3066.html">N3066</a>. -</p> - - -<p><b>Proposed resolution:</b></p> - -<p> -In section 24.1.4 [lib.bidirectdional.iterators], change the return -type in table 75 from "convertible to <tt>T</tt>" to -<tt>T&</tt>. -</p> - -<p> -In section 24.1.5 [lib.random.access.iterators], change the -operational semantics for <tt>a[n]</tt> to " the r-value of -<tt>a[n]</tt> is equivalent to the r-value of <tt>*(a + -n)</tt>". Add a new row in the table for the expression <tt>a[n] = t</tt> -with a return type of convertible to <tt>T</tt> and operational semantics of -<tt>*(a + n) = t</tt>. -</p> - -<p><i>[Lillehammer: Real problem, but should be addressed as part of - iterator redesign]</i></p> - - - - -<p><b>Rationale:</b></p> -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote><p> -Solved by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2758.pdf">N2758</a>. -</p></blockquote> - - - - - - - -<hr> -<h3><a name="302"></a>302. Need error indication from codecvt<>::do_length</h3> -<p><b>Section:</b> 22.4.1.5 [locale.codecvt.byname] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Gregory Bumgardner <b>Opened:</b> 2001-01-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt.byname">issues</a> in [locale.codecvt.byname].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The effects of <tt>codecvt<>::do_length()</tt> are described in -22.2.1.5.2, paragraph 10. As implied by that paragraph, and clarified -in issue <a href="lwg-defects.html#75">75</a>, <tt>codecvt<>::do_length()</tt> must -process the source data and update the <tt>stateT</tt> argument just -as if the data had been processed by <tt>codecvt<>::in()</tt>. -However, the standard does not specify how <tt>do_length()</tt> would -report a translation failure, should the source sequence contain -untranslatable or illegal character sequences. -</p> - -<p> -The other conversion methods return an "error" result value -to indicate that an untranslatable character has been encountered, but -<tt>do_length()</tt> already has a return value (the number of source -characters that have been processed by the method). -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -This issue cannot be resolved without modifying the interface. An exception -cannot be used, as there would be no way to determine how many characters -have been processed and the state object would be left in an indeterminate -state. -</p> - -<p> -A source compatible solution involves adding a fifth argument to length() -and do_length() that could be used to return position of the offending -character sequence. This argument would have a default value that would -allow it to be ignored: -</p> - -<pre> - int length(stateT& state, - const externT* from, - const externT* from_end, - size_t max, - const externT** from_next = 0); - - virtual - int do_length(stateT& state, - const externT* from, - const externT* from_end, - size_t max, - const externT** from_next); -</pre> - -<p> -Then an exception could be used to report any translation errors and -the from_next argument, if used, could then be used to retrieve the -location of the offending character sequence. -</p> - - -<p><b>Rationale:</b></p> -<p>The standard is already clear: the return value is the number of -"valid complete characters". If it encounters an invalid sequence of -external characters, it stops.</p> - - - - - -<hr> -<h3><a name="304"></a>304. Must <tt>*a</tt> return an lvalue when <tt>a</tt> is an input iterator?</h3> -<p><b>Section:</b> X [iterator.concepts] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Dave Abrahams <b>Opened:</b> 2001-02-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iterator.concepts">issues</a> in [iterator.concepts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -We all "know" that input iterators are allowed to produce -values when dereferenced of which there is no other in-memory copy. -</p> - -<p> -But: Table 72, with a careful reading, seems to imply that this can only be -the case if the value_type has no members (e.g. is a built-in type). -</p> - -<p>The problem occurs in the following entry:</p> - -<pre> - a->m pre: (*a).m is well-defined - Equivalent to (*a).m -</pre> - -<p> -<tt>*a.m</tt> can be well-defined if <tt>*a</tt> is not a reference -type, but since <tt>operator->()</tt> must return a pointer for -<tt>a->m</tt> to be well-formed, it needs something to return a -pointer <i>to</i>. This seems to indicate that <tt>*a</tt> must be -buffered somewhere to make a legal input iterator. -</p> - -<p>I don't think this was intentional.</p> - - -<p><b>Rationale:</b></p> -<p>The current standard is clear and consistent. Input iterators that - return rvalues are in fact implementable. They may in some cases - require extra work, but it is still possible to define an operator-> - in such cases: it doesn't have to return a T*, but may return a - proxy type. No change to the standard is justified.</p> - - - - - -<hr> -<h3><a name="309"></a>309. Does sentry catch exceptions?</h3> -<p><b>Section:</b> 27.7 [iostream.format] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2001-03-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iostream.format">issues</a> in [iostream.format].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The descriptions of the constructors of basic_istream<>::sentry -(27.7.2.1.3 [istream::sentry]) and basic_ostream<>::sentry -(27.7.3.4 [ostream::sentry]) do not explain what the functions do in -case an exception is thrown while they execute. Some current -implementations allow all exceptions to propagate, others catch them -and set ios_base::badbit instead, still others catch some but let -others propagate. -</p> - -<p> -The text also mentions that the functions may call setstate(failbit) -(without actually saying on what object, but presumably the stream -argument is meant). That may have been fine for -basic_istream<>::sentry prior to issue <a href="lwg-defects.html#195">195</a>, since -the function performs an input operation which may fail. However, -issue <a href="lwg-defects.html#195">195</a> amends 27.7.2.1.3 [istream::sentry], p2 to -clarify that the function should actually call setstate(failbit | -eofbit), so the sentence in p3 is redundant or even somewhat -contradictory. -</p> - -<p> -The same sentence that appears in 27.7.3.4 [ostream::sentry], p3 -doesn't seem to be very meaningful for basic_istream<>::sentry -which performs no input. It is actually rather misleading since it -would appear to guide library implementers to calling -setstate(failbit) when os.tie()->flush(), the only called function, -throws an exception (typically, it's badbit that's set in response to -such an event). -</p> - -<p><b>Additional comments from Martin, who isn't comfortable with the - current proposed resolution</b> (see c++std-lib-11530)</p> - -<p> -The istream::sentry ctor says nothing about how the function -deals with exemptions (27.6.1.1.2, p1 says that the class is -responsible for doing "exception safe"(*) prefix and suffix -operations but it doesn't explain what level of exception -safety the class promises to provide). The mockup example -of a "typical implementation of the sentry ctor" given in -27.6.1.1.2, p6, removed in ISO/IEC 14882:2003, doesn't show -exception handling, either. Since the ctor is not classified -as a formatted or unformatted input function, the text in -27.6.1.1, p1 through p4 does not apply. All this would seem -to suggest that the sentry ctor should not catch or in any -way handle exceptions thrown from any functions it may call. -Thus, the typical implementation of an istream extractor may -look something like [1]. -</p> - -<p> -The problem with [1] is that while it correctly sets ios::badbit -if an exception is thrown from one of the functions called from -the sentry ctor, if the sentry ctor reaches EOF while extracting -whitespace from a stream that has eofbit or failbit set in -exceptions(), it will cause an ios::failure to be thrown, which -will in turn cause the extractor to set ios::badbit. -</p> - -<p> -The only straightforward way to prevent this behavior is to -move the definition of the sentry object in the extractor -above the try block (as suggested by the example in 22.2.8, -p9 and also indirectly supported by 27.6.1.3, p1). See [2]. -But such an implementation will allow exceptions thrown from -functions called from the ctor to freely propagate to the -caller regardless of the setting of ios::badbit in the stream -object's exceptions(). -</p> - -<p> -So since neither [1] nor [2] behaves as expected, the only -possible solution is to have the sentry ctor catch exceptions -thrown from called functions, set badbit, and propagate those -exceptions if badbit is also set in exceptions(). (Another -solution exists that deals with both kinds of sentries, but -the code is non-obvious and cumbersome -- see [3].) -</p> - -<p> -Please note that, as the issue points out, current libraries -do not behave consistently, suggesting that implementors are -not quite clear on the exception handling in istream::sentry, -despite the fact that some LWG members might feel otherwise. -(As documented by the parenthetical comment here: -http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1480.html#309) -</p> - -<p> -Also please note that those LWG members who in Copenhagen -felt that "a sentry's constructor should not catch exceptions, -because sentries should only be used within (un)formatted input -functions and that exception handling is the responsibility of -those functions, not of the sentries," as noted here -http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2001/n1310.html#309 -would in effect be either arguing for the behavior described -in [1] or for extractors implemented along the lines of [3]. -</p> - -<p> -The original proposed resolution (Revision 25 of the issues -list) clarifies the role of the sentry ctor WRT exception -handling by making it clear that extractors (both library -or user-defined) should be implemented along the lines of -[2] (as opposed to [1]) and that no exception thrown from -the callees should propagate out of either function unless -badbit is also set in exceptions(). -</p> - - -<p>[1] Extractor that catches exceptions thrown from sentry:</p> - -<blockquote> -<pre> -struct S { long i; }; - -istream& operator>> (istream &strm, S &s) -{ - ios::iostate err = ios::goodbit; - try { - const istream::sentry guard (strm, false); - if (guard) { - use_facet<num_get<char> >(strm.getloc ()) - .get (istreambuf_iterator<char>(strm), - istreambuf_iterator<char>(), - strm, err, s.i); - } - } - catch (...) { - bool rethrow; - try { - strm.setstate (ios::badbit); - rethrow = false; - } - catch (...) { - rethrow = true; - } - if (rethrow) - throw; - } - if (err) - strm.setstate (err); - return strm; -} -</pre> -</blockquote> - -<p>[2] Extractor that propagates exceptions thrown from sentry:</p> - -<blockquote> -<pre> -istream& operator>> (istream &strm, S &s) -{ - istream::sentry guard (strm, false); - if (guard) { - ios::iostate err = ios::goodbit; - try { - use_facet<num_get<char> >(strm.getloc ()) - .get (istreambuf_iterator<char>(strm), - istreambuf_iterator<char>(), - strm, err, s.i); - } - catch (...) { - bool rethrow; - try { - strm.setstate (ios::badbit); - rethrow = false; - } - catch (...) { - rethrow = true; - } - if (rethrow) - throw; - } - if (err) - strm.setstate (err); - } - return strm; -} -</pre> -</blockquote> - -<p> -[3] Extractor that catches exceptions thrown from sentry -but doesn't set badbit if the exception was thrown as a -result of a call to strm.clear(). -</p> - -<blockquote> -<pre> -istream& operator>> (istream &strm, S &s) -{ - const ios::iostate state = strm.rdstate (); - const ios::iostate except = strm.exceptions (); - ios::iostate err = std::ios::goodbit; - bool thrown = true; - try { - const istream::sentry guard (strm, false); - thrown = false; - if (guard) { - use_facet<num_get<char> >(strm.getloc ()) - .get (istreambuf_iterator<char>(strm), - istreambuf_iterator<char>(), - strm, err, s.i); - } - } - catch (...) { - if (thrown && state & except) - throw; - try { - strm.setstate (ios::badbit); - thrown = false; - } - catch (...) { - thrown = true; - } - if (thrown) - throw; - } - if (err) - strm.setstate (err); - - return strm; -} -</pre> -</blockquote> - -<p> -[Pre-Berlin] Reopened at the request of Paolo Carlini and Steve Clamage. -</p> - -<p> -[Pre-Portland] A relevant newsgroup post: -</p> - -<p> -The current proposed resolution of issue #309 -(http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#309) is -unacceptable. I write commerical software and coding around this -makes my code ugly, non-intuitive, and requires comments referring -people to this very issue. Following is the full explanation of my -experience. -</p> -<p> -In the course of writing software for commercial use, I constructed -std::ifstream's based on user-supplied pathnames on typical POSIX -systems. -</p> -<p> -It was expected that some files that opened successfully might not read -successfully -- such as a pathname which actually refered to a -directory. Intuitively, I expected the streambuffer underflow() code -to throw an exception in this situation, and recent implementations of -libstdc++'s basic_filebuf do just that (as well as many of my own -custom streambufs). -</p> -<p> -I also intuitively expected that the istream code would convert these -exceptions to the "badbit' set on the stream object, because I had not -requested exceptions. I refer to 27.6.1.1. P4. -</p> -<p> -However, this was not the case on at least two implementations -- if -the first thing I did with an istream was call operator>>( T& ) for T -among the basic arithmetic types and std::string. Looking further I -found that the sentry's constructor was invoking the exception when it -pre-scanned for whitespace, and the extractor function (operator>>()) -was not catching exceptions in this situation. -</p> -<p> -So, I was in a situation where setting 'noskipws' would change the -istream's behavior even though no characters (whitespace or not) could -ever be successfully read. -</p> -<p> -Also, calling .peek() on the istream before calling the extractor() -changed the behavior (.peek() had the effect of setting the badbit -ahead of time). -</p> -<p> -I found this all to be so inconsistent and inconvenient for me and my -code design, that I filed a bugzilla entry for libstdc++. I was then -told that the bug cannot be fixed until issue #309 is resolved by the -committee. -</p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -Moved to NAD. -</p> -<p> -See the rationale in the issue. Paolo, who requested that the issue be -reopened, agreed with the rationale. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>The LWG agrees there is minor variation between implementations, - but believes that it doesn't matter. This is a rarely used corner - case. There is no evidence that this has any commercial importance - or that it causes actual portability problems for customers trying - to write code that runs on multiple implementations.</p> - - - - - -<hr> -<h3><a name="313"></a>313. set_terminate and set_unexpected question</h3> -<p><b>Section:</b> 18.8.3.4 [terminate] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Judy Ward <b>Opened:</b> 2001-04-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#terminate">issues</a> in [terminate].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -According to section 18.7.3.3 of the standard, std::terminate() is -supposed to call the terminate_handler in effect immediately after -evaluating the throw expression. -</p> - -<p> -Question: what if the terminate_handler in effect is itself -std::terminate? -</p> - -<p>For example:</p> - -<pre> - #include <exception> - - int main () { - std::set_terminate(std::terminate); - throw 5; - return 0; - } -</pre> - -<p> -Is the implementation allowed to go into an infinite loop? -</p> - -<p> -I think the same issue applies to std::set_unexpected. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>Infinite recursion is to be expected: users who set the terminate -handler to <tt>terminate</tt> are explicitly asking for <tt>terminate</tt> -to call itself.</p> - - - - - -<hr> -<h3><a name="314"></a>314. Is the stack unwound when terminate() is called?</h3> -<p><b>Section:</b> 18.8.3.4 [terminate] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Detlef Vollmann <b>Opened:</b> 2001-04-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#terminate">issues</a> in [terminate].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -The standard appears to contradict itself about whether the stack is -unwound when the implementation calls terminate(). -</p> - -<p>From 18.7.3.3p2:</p> -<blockquote><p> - Calls the terminate_handler function in effect immediately - after evaluating the throw-expression (lib.terminate.handler), - if called by the implementation [...] -</p></blockquote> - -<p>So the stack is guaranteed not to be unwound.</p> - -<p>But from 15.3p9:</p> -<blockquote><p> - [...]whether or not the stack is unwound before this call - to terminate() is implementation-defined (except.terminate). -</p></blockquote> - -<p> -And 15.5.1 actually defines that in most cases the stack is unwound. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>There is definitely no contradiction between the core and library -clauses; nothing in the core clauses says that stack unwinding happens -after <tt>terminate</tt> is called. 18.7.3.3p2 does not say anything -about when terminate() is called; it merely specifies which -<tt>terminate_handler</tt> is used.</p> - - - - - -<hr> -<h3><a name="323"></a>323. <tt>abs()</tt> overloads in different headers</h3> -<p><b>Section:</b> 26.8 [c.math] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Dave Abrahams <b>Opened:</b> 2001-06-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.math">active issues</a> in [c.math].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Currently the standard mandates the following overloads of -abs():</p> - -<pre> - abs(long), abs(int) in <cstdlib> - - abs(float), abs(double), abs(long double) in <cmath> - - template<class T> T abs(const complex<T>&) in <complex> - - template<class T> valarray<T> abs(const valarray<T>&); in <valarray> -</pre> - -<p> -The problem is that having only some overloads visible of a function -that works on "implicitly inter-convertible" types is dangerous in -practice. The headers that get included at any point in a translation -unit can change unpredictably during program -development/maintenance. The wrong overload might be unintentionally -selected. -</p> - -<p> -Currently, there is nothing that mandates the simultaneous visibility -of these overloads. Indeed, some vendors have begun fastidiously -reducing dependencies among their (public) headers as a QOI issue: it -helps people to write portable code by refusing to compile unless all -the correct headers are #included. -</p> - -<p>The same issue may exist for other functions in the library.</p> - -<p>Redmond: PJP reports that C99 adds two new kinds of <tt>abs</tt>: <tt>complex</tt>, -and <tt>int_max_abs</tt>.</p> - -<p>Related issue: <a href="lwg-defects.html#343">343</a>.</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -The situation is not sufficiently severe to warrant a change. -</p></blockquote> - - - - -<p><b>Rationale:</b></p> -<p>The programs that could potentially be broken by this situation are - already fragile, and somewhat contrived: For example, a user-defined - class that has conversion overloads both to <tt>long</tt> and - to <tt>float</tt>. If <tt>x</tt> is a value of such a class, then - <tt>abs(x)</tt> would give the <tt>long</tt> version if the user - included <cstdlib>, the <tt>float</tt> version if the user - included <cmath>, and would be diagnosed as ambiguous at - compile time if the user included both headers. The LWG couldn't - find an example of a program whose meaning would be changed (as - opposed to changing it from well-formed to ill-formed) simply by - adding another standard header.</p> - -<p>Since the harm seems minimal, and there don't seem to be any simple - and noninvasive solutions, this is being closed as NAD. It is - marked as "Future" for two reasons. First, it might be useful to - define an <tt><all></tt> header that would include all - Standard Library headers. Second, we should at least make sure that - future library extensions don't make this problem worse.</p> - - - - - -<hr> -<h3><a name="326"></a>326. Missing typedef in moneypunct_byname</h3> -<p><b>Section:</b> 22.4.6.4 [locale.moneypunct.byname] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2001-07-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The definition of the moneypunct facet contains the typedefs char_type -and string_type. Only one of these names, string_type, is defined in -the derived facet, moneypunct_byname.</p> - - -<p><b>Proposed resolution:</b></p> -<p>For consistency with the numpunct facet, add a typedef for -char_type to the definition of the moneypunct_byname facet in -22.4.6.4 [locale.moneypunct.byname].</p> - - -<p><b>Rationale:</b></p> -<p>The absence of the typedef is irrelevant. Users can still access -the typedef, because it is inherited from the base class.</p> - - - - - -<hr> -<h3><a name="330"></a>330. Misleading "exposition only" value in class locale definition</h3> -<p><b>Section:</b> 22.3.1 [locale] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2001-07-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale">issues</a> in [locale].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The "exposition only" value of the std::locale::none constant shown in -the definition of class locale is misleading in that it on many -systems conflicts with the value assigned to one if the LC_XXX -constants (specifically, LC_COLLATE on AIX, LC_ALL on HP-UX, LC_CTYPE -on Linux and SunOS). This causes incorrect behavior when such a -constant is passed to one of the locale member functions that accept a -locale::category argument and interpret it as either the C LC_XXX -constant or a bitmap of locale::category values. At least three major -implementations adopt the suggested value without a change and -consequently suffer from this problem. -</p> - -<p> -For instance, the following code will (presumably) incorrectly copy facets -belonging to the collate category from the German locale on AIX: -</p> - -<pre> - std::locale l (std::locale ("C"), "de_DE", std::locale::none); -</pre> - - -<p><b>Rationale:</b></p> -<p>The LWG agrees that it may be difficult to implement locale member -functions in such a way that they can take either <tt>category</tt> -arguments or the LC_ constants defined in <cctype>. In light of -this requirement (22.3.1.1.1 [locale.category], paragraph 2), and in light -of the requirement in the preceding paragraph that it is possible to -combine <tt>category</tt> bitmask elements with bitwise operations, -defining the <tt>category</tt> elements is delicate, -particularly if an implementor is constrained to work with a -preexisting C library. (Just using the existing LC_ constants would -not work in general.) There's no set of "exposition only" values that -could give library implementors proper guidance in such a delicate -matter. The non-normative example we're giving is no worse than -any other choice would be.</p> - -<p>See issue <a href="lwg-defects.html#347">347</a>.</p> - - - - - -<hr> -<h3><a name="332"></a>332. Consider adding increment and decrement operators to std::fpos< T > </h3> -<p><b>Section:</b> 27.5.4 [fpos] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> PremAnand M. Rao <b>Opened:</b> 2001-08-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#fpos">issues</a> in [fpos].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Increment and decrement operators are missing from -Table 88 -- Position type requirements in 27.5.4 [fpos]. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Table 88 (section 27.4.3) -- Position type requirements -be updated to include increment and decrement operators. -</p> - -<pre> -expression return type operational note - -++p fpos& p += O(1) -p++ fpos { P tmp = p; - ++p; - return tmp; } ---p fpos& p -= O(1) -p-- fpos { P tmp = p; - --p; - return tmp; } -</pre> - - - -<p><b>Rationale:</b></p> -<p>The LWG believes this is a request for extension, not a defect -report. Additionally, nobody saw a clear need for this extension; -<tt>fpos</tt> is used only in very limited ways.</p> - - - - - -<hr> -<h3><a name="342"></a>342. seek and eofbit</h3> -<p><b>Section:</b> 27.7.2.3 [istream.unformatted] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2001-10-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#istream.unformatted">active issues</a> in [istream.unformatted].</p> -<p><b>View all other</b> <a href="lwg-index.html#istream.unformatted">issues</a> in [istream.unformatted].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>I think we have a defect.</p> - -<p>According to lwg issue <a href="lwg-defects.html#60">60</a> which is now a dr, the -description of seekg in 27.7.2.3 [istream.unformatted] paragraph 38 now looks -like:</p> - -<blockquote><p> -Behaves as an unformatted input function (as described in 27.6.1.3, -paragraph 1), except that it does not count the number of characters -extracted and does not affect the value returned by subsequent calls to -gcount(). After constructing a sentry object, if fail() != true, -executes rdbuf()->pubseekpos( pos). -</p></blockquote> - -<p>And according to lwg issue <a href="lwg-defects.html#243">243</a> which is also now a dr, -27.6.1.3, paragraph 1 looks like:</p> - -<blockquote><p> -Each unformatted input function begins execution by constructing an -object of class sentry with the default argument noskipws (second) -argument true. If the sentry object returns true, when converted to a -value of type bool, the function endeavors to obtain the requested -input. Otherwise, if the sentry constructor exits by throwing an -exception or if the sentry object returns false, when converted to a -value of type bool, the function returns without attempting to obtain -any input. In either case the number of extracted characters is set to -0; unformatted input functions taking a character array of non-zero -size as an argument shall also store a null character (using charT()) -in the first location of the array. If an exception is thrown during -input then ios::badbit is turned on in *this'ss error state. If -(exception()&badbit)!= 0 then the exception is rethrown. It also counts -the number of characters extracted. If no exception has been thrown it -ends by storing the count in a member object and returning the value -specified. In any event the sentry object is destroyed before leaving -the unformatted input function. -</p></blockquote> - -<p>And finally 27.6.1.1.2/5 says this about sentry:</p> - -<blockquote><p> -If, after any preparation is completed, is.good() is true, ok_ != false -otherwise, ok_ == false. -</p></blockquote> - -<p> -So although the seekg paragraph says that the operation proceeds if -!fail(), the behavior of unformatted functions says the operation -proceeds only if good(). The two statements are contradictory when only -eofbit is set. I don't think the current text is clear which condition -should be respected. -</p> - -<p><b>Further discussion from Redmond:</b></p> - -<p>PJP: It doesn't seem quite right to say that <tt>seekg</tt> is -"unformatted". That makes specific claims about sentry that -aren't quite appropriate for seeking, which has less fragile failure -modes than actual input. If we do really mean that it's unformatted -input, it should behave the same way as other unformatted input. On -the other hand, "principle of least surprise" is that seeking from EOF -ought to be OK.</p> - -<p> -Pre-Berlin: Paolo points out several problems with the proposed resolution in -Ready state: -</p> - -<ul> -<li>It should apply to both overloads of seekg.</li> -<li>tellg has similar issues, except that it should not call clear().</li> -<li>The point about clear() seems to apply to seekp().</li> -<li>Depending on the outcome of <a href="lwg-defects.html#419">419</a> -if the sentry -sets <tt>failbit</tt> when it finds <tt>eofbit</tt> already set, then -you can never seek away from the end of stream.</li> -</ul> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -Moved to NAD. Will reopen if proposed resolution is supplied. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - -<p>Change 27.7.2.3 [istream.unformatted] to:</p> -<blockquote><p> -Behaves as an unformatted input function (as described in 27.6.1.3, -paragraph 1), except that it does not count the number of characters -extracted, does not affect the value returned by subsequent calls to -gcount(), and does not examine the value returned by the sentry -object. After constructing a sentry object, if <tt>fail() != -true</tt>, executes <tt>rdbuf()->pubseekpos(pos)</tt>. In -case of success, the function calls clear(). -In case of failure, the function calls <tt>setstate(failbit)</tt> -(which may throw <tt>ios_base::failure</tt>). -</p></blockquote> - -<p><i>[Lillehammer: Matt provided wording.]</i></p> - - - - -<p><b>Rationale:</b></p> -<p>In C, fseek does clear EOF. This is probably what most users would - expect. We agree that having eofbit set should not deter a seek, - and that a successful seek should clear eofbit. Note - that <tt>fail()</tt> is true only if <tt>failbit</tt> - or <tt>badbit</tt> is set, so using <tt>!fail()</tt>, rather - than <tt>good()</tt>, satisfies this goal.</p> - - - - - -<hr> -<h3><a name="344"></a>344. grouping + showbase</h3> -<p><b>Section:</b> 22.4.2 [category.numeric] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2001-10-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -When both grouping and showbase are active and the basefield is octal, -does the leading 0 participate in the grouping or not? For example, -should one format as: 0,123,456 or 0123,456? -</p> -<p> -An analogy can be drawn with hexadecimal. It appears that 0x123,456 is -preferred over 0x,123,456. However, this analogy is not universally -accepted to apply to the octal base. The standard is not clear on how -to format (or parse) in this manner. -</p> - -<p><b>Proposed resolution:</b></p> -<p> -Insert into 22.4.3.1.2 [facet.numpunct.virtuals] paragraph 3, just before the last -sentence: -</p> -<blockquote><p> -The leading hexadecimal base specifier "0x" does not participate in -grouping. The leading '0' octal base specifier may participate in -grouping. It is unspecified if the leading '0' participates in -formatting octal numbers. In parsing octal numbers, the implementation -is encouraged to accept both the leading '0' participating in the -grouping, and not participating (e.g. 0123,456 or 0,123,456). -</p></blockquote> - -<p><b>Rationale:</b></p> -<p> -The current behavior may be unspecified, but it's not clear that it -matters. This is an obscure corner case, since grouping is usually -intended for the benefit of humans and oct/hex prefixes are usually -intended for the benefit of machines. There is not a strong enough -consensus in the LWG for action. -</p> - - - - -<hr> -<h3><a name="348"></a>348. Minor issue with std::pair operator<</h3> -<p><b>Section:</b> 20.3 [pairs] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Andy Sawyer <b>Opened:</b> 2001-10-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#pairs">issues</a> in [pairs].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-active.html#532">532</a></p> -<p><b>Discussion:</b></p> - - -<p> -The current wording of 20.2.2 [lib.pairs] p6 precludes the use of -operator< on any pair type which contains a pointer. -</p> - - -<p><b>Proposed resolution:</b></p> -<p>In 20.3 [pairs] paragraph 6, replace:</p> -<pre> - Returns: x.first < y.first || (!(y.first < x.first) && x.second < - y.second). -</pre> -<p>With:</p> -<pre> - Returns: std::less<T1>()( x.first, y.first ) || - (!std::less<T1>()( y.first, x.first) && - std::less<T2>()( x.second, y.second ) ) -</pre> - - - -<p><b>Rationale:</b></p> -<p>This is an instance of a much more general problem. If we want - operator< to translate to std::less for pairs of pointers, where - do we draw the line? The same issue applies to individual - pointers, smart pointer wrappers, std::vector<T*>, and so - on.</p> - -<p>Andy Koenig suggests that the real issue here is that we aren't - distinguishing adequately between two different orderings, a - "useful ordering" and a "canonical ordering" that's used just - because we sometimes need <i>some</i> ordering without caring much - which ordering it is. Another example of the later is typeinfo's - <tt>before</tt>.</p> - - - - - - -<hr> -<h3><a name="350"></a>350. allocator<>::address</h3> -<p><b>Section:</b> 20.7.9.1 [allocator.members], 17.6.3.5 [allocator.requirements], 17.6.1.1 [contents] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Nathan Myers <b>Opened:</b> 2001-10-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#allocator.members">issues</a> in [allocator.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#634">634</a></p> -<p><b>Discussion:</b></p> -<p>See c++std-lib-9006 and c++std-lib-9007. This issue is taken -verbatim from -9007.</p> - -<p> -The core language feature allowing definition of operator&() applied -to any non-builtin type makes that operator often unsafe to use in -implementing libraries, including the Standard Library. The result -is that many library facilities fail for legal user code, such as -the fragment</p> -<pre> - class A { private: A* operator&(); }; - std::vector<A> aa; - - class B { }; - B* operator&(B&) { return 0; } - std::vector<B> ba; -</pre> - -<p> -In particular, the requirements table for Allocator (Table 32) specifies -no semantics at all for member address(), and allocator<>::address is -defined in terms of unadorned operator &. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p> -In 20.6.1.1, Change the definition of allocator<>::address from:</p> -<blockquote><p> - Returns: &x -</p></blockquote> - -<p>to:</p> - -<p> - Returns: The value that the built in operator&(x) would return if not - overloaded. -</p> - -<p> -In 20.1.6, Table 32, add to the Notes column of the a.address(r) and -a.address(s) lines, respectively: -</p> - -<pre> - allocator<T>::address(r) - allocator<T>::address(s) -</pre> - -<p>In addition, in clause 17.4.1.1, add a statement:</p> - -<blockquote><p> - The Standard Library does not apply operator& to any type for which - operator& may be overloaded. -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p>The LWG believes both examples are ill-formed. The contained type -is required to be CopyConstructible (17.6.3.1 [utility.arg.requirements]), and that -includes the requirement that &t return the usual types and -values. Since allocators are intended to be used in conjunction with -containers, and since the CopyConstructible requirements appear to -have been written to deal with the concerns of this issue, the LWG -feels it is NAD unless someone can come up with a well-formed example -exhibiting a problem.</p> - -<p>It may well be that the CopyConstructible requirements are too - restrictive and that either the container requirements or the - CopyConstructive requirements should be relaxed, but that's a far - larger issue. Marking this issue as "future" as a pointer to that - larger issue.</p> - - - - - -<hr> -<h3><a name="351"></a>351. unary_negate and binary_negate: struct or class?</h3> -<p><b>Section:</b> 20.9 [function.objects] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Dale Riley <b>Opened:</b> 2001-11-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#function.objects">issues</a> in [function.objects].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In 20.9 [function.objects] the header <functional> synopsis declares -the unary_negate and binary_negate function objects as struct. -However in 20.9.9 [negators] the unary_negate and binary_negate -function objects are defined as class. Given the context, they are -not "basic function objects" like negate, so this is either a typo or -an editorial oversight. -</p> - -<p><i>[Taken from comp.std.c++]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p>Change the synopsis to reflect the useage in 20.9.9 [negators]</p> - -<p><i>[Curaçao: Since the language permits "struct", the LWG -views this as NAD. They suggest, however, that the Project Editor -might wish to make the change as editorial.]</i></p> - - - - - - - -<hr> -<h3><a name="356"></a>356. Meaning of ctype_base::mask enumerators</h3> -<p><b>Section:</b> 22.4.1 [category.ctype] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2002-01-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#category.ctype">issues</a> in [category.ctype].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p>What should the following program print?</p> - -<pre> - #include <locale> - #include <iostream> - - class my_ctype : public std::ctype<char> - { - typedef std::ctype<char> base; - public: - my_ctype(std::size_t refs = 0) : base(my_table, false, refs) - { - std::copy(base::classic_table(), base::classic_table() + base::table_size, - my_table); - my_table[(unsigned char) '_'] = (base::mask) (base::print | base::space); - } - private: - mask my_table[base::table_size]; - }; - - int main() - { - my_ctype ct; - std::cout << "isspace: " << ct.is(std::ctype_base::space, '_') << " " - << "isalpha: " << ct.is(std::ctype_base::alpha, '_') << std::endl; - } -</pre> - -<p>The goal is to create a facet where '_' is treated as whitespace.</p> - -<p>On gcc 3.0, this program prints "isspace: 1 isalpha: 0". On -Microsoft C++ it prints "isspace: 1 isalpha: 1".</p> - -<p> -I believe that both implementations are legal, and the standard does not -give enough guidance for users to be able to use std::ctype's -protected interface portably.</p> - -<p> -The above program assumes that ctype_base::mask enumerators like -<tt>space</tt> and <tt>print</tt> are disjoint, and that the way to -say that a character is both a space and a printing character is to or -those two enumerators together. This is suggested by the "exposition -only" values in 22.4.1 [category.ctype], but it is nowhere specified in -normative text. An alternative interpretation is that the more -specific categories subsume the less specific. The above program -gives the results it does on the Microsoft compiler because, on that -compiler, <tt>print</tt> has all the bits set for each specific -printing character class. -</p> - -<p>From the point of view of std::ctype's public interface, there's no -important difference between these two techniques. From the point of -view of the protected interface, there is. If I'm defining a facet -that inherits from std::ctype<char>, I'm the one who defines the -value that table()['a'] returns. I need to know what combination of -mask values I should use. This isn't so very esoteric: it's exactly -why std::ctype has a protected interface. If we care about users -being able to write their own ctype facets, we have to give them a -portable way to do it. -</p> - -<p> -Related reflector messages: -lib-9224, lib-9226, lib-9229, lib-9270, lib-9272, lib-9273, lib-9274, -lib-9277, lib-9279. -</p> - -<p>Issue <a href="lwg-defects.html#339">339</a> is related, but not identical. The -proposed resolution if issue <a href="lwg-defects.html#339">339</a> says that -ctype_base::mask must be a bitmask type. It does not say that the -ctype_base::mask elements are bitmask elements, so it doesn't -directly affect this issue.</p> - -<p>More comments from Benjamin Kosnik, who believes that -that C99 compatibility essentially requires what we're -calling option 1 below.</p> - -<blockquote> -<pre> -I think the C99 standard is clear, that isspace -> !isalpha. --------- - -#include <locale> -#include <iostream> - -class my_ctype : public std::ctype<char> -{ -private: - typedef std::ctype<char> base; - mask my_table[base::table_size]; - -public: - my_ctype(std::size_t refs = 0) : base(my_table, false, refs) - { - std::copy(base::classic_table(), base::classic_table() + base::table_size, - my_table); - mask both = base::print | base::space; - my_table[static_cast<mask>('_')] = both; - } -}; - -int main() -{ - using namespace std; - my_ctype ct; - cout << "isspace: " << ct.is(ctype_base::space, '_') << endl; - cout << "isprint: " << ct.is(ctype_base::print, '_') << endl; - - // ISO C99, isalpha iff upper | lower set, and !space. - // 7.5, p 193 - // -> looks like g++ behavior is correct. - // 356 -> bitmask elements are required for ctype_base - // 339 -> bitmask type required for mask - cout << "isalpha: " << ct.is(ctype_base::alpha, '_') << endl; -} -</pre> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p>Informally, we have three choices:</p> -<ol> -<li>Require that the enumerators are disjoint (except for alnum and -graph)</li> -<li>Require that the enumerators are not disjoint, and specify which -of them subsume which others. (e.g. mandate that lower includes alpha -and print)</li> -<li>Explicitly leave this unspecified, which the result that the above -program is not portable.</li> -</ol> - -<p>Either of the first two options is just as good from the standpoint -of portability. Either one will require some implementations to -change.</p> - - -<p><b>Rationale:</b></p> -<p>The LWG agrees that this is a real ambiguity, and that both -interpretations are conforming under the existing standard. However, -there's no evidence that it's causing problems for real users. Users -who want to define ctype facets portably can test the ctype_base masks -to see which interpretation is being used.</p> - - - - - -<hr> -<h3><a name="357"></a>357. <cmath> float functions cannot return HUGE_VAL</h3> -<p><b>Section:</b> 26.8 [c.math] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Ray Lischner <b>Opened:</b> 2002-02-26 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.math">active issues</a> in [c.math].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The float versions of the math functions have no meaningful value to return -for a range error. The long double versions have a value they can return, -but it isn't necessarily the most reasonable value. -</p> - -<p> -Section 26.5 [lib.c.math], paragraph 5, says that C++ "adds float and long -double overloaded versions of these functions, with the same semantics," -referring to the math functions from the C90 standard. -</p> - -<p> -The C90 standard, in section 7.5.1, paragraph 3, says that functions return -"the value of the macro HUGE_VAL" when they encounter a range error. -Section 7.5, paragraph 2, defines HUGE_VAL as a macro that "expands to a -positive double expression, not necessarily representable as a float." -</p> - -<p> -Therefore, the float versions of the math functions have no way to -signal a range error. <i>[Curaçao: The LWG notes that this isn't -strictly correct, since errno is set.]</i> The semantics require that they -return HUGE_VAL, but they cannot because HUGE_VAL might not be -representable as a float. -</p> - -<p> -The problem with long double functions is less severe because HUGE_VAL is -representable as a long double. On the other hand, it might not be a "huge" -long double value, and might fall well within the range of normal return -values for a long double function. Therefore, it does not make sense for a -long double function to return a double (HUGE_VAL) for a range error. -</p> - - -<p><b>Proposed resolution:</b></p> -<p>Curaçao: C99 was faced with a similar problem, which they fixed by -adding HUGE_VALF and HUGE_VALL in addition to HUGE_VAL.</p> - -<p>C++ must also fix, but it should be done in the context of the -general C99 based changes to C++, not via DR. Thus the LWG in Curaçao -felt the resolution should be NAD, FUTURE, but the issue is being held -open for one more meeting to ensure LWG members not present during the -discussion concur.</p> - - -<p><b>Rationale:</b></p> -<p>Will be fixed as part of more general work in the TR.</p> - - - - - -<hr> -<h3><a name="361"></a>361. num_get<>::do_get (..., void*&) checks grouping</h3> -<p><b>Section:</b> 22.4.2.2.2 [facet.num.put.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2002-03-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#facet.num.put.virtuals">issues</a> in [facet.num.put.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -22.2.2.2.2, p12 specifies that <tt>thousands_sep</tt> is to be inserted only -for integral types (issue 282 suggests that this should be done for -all arithmetic types). -</p> - -<p> -22.2.2.1.2, p12 requires that grouping be checked for all extractors -including that for <tt>void*</tt>. -</p> - -<p> -I don't think that's right. <tt>void*</tt> values should not be checked for -grouping, should they? (Although if they should, then <tt>num_put</tt> needs -to write them out, otherwise their extraction will fail.) -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change the first sentence of 22.2.2.2.2, p12 from -</p> -<blockquote><p> - Digit grouping is checked. That is, the positions of discarded - separators is examined for consistency with - use_facet<numpunct<charT> >(loc).grouping(). - If they are not consistent then ios_base::failbit is assigned - to err. -</p></blockquote> - -<p>to</p> -<blockquote><p> - Except for conversions to void*, digit grouping is checked... -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p>This would be a change: as it stands, the standard clearly - specifies that grouping applies to void*. A survey of existing - practice shows that most existing implementations do that, as they - should.</p> - - - - - -<hr> -<h3><a name="366"></a>366. Excessive const-qualification</h3> -<p><b>Section:</b> 27 [input.output] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Walter Brown, Marc Paterno <b>Opened:</b> 2002-05-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#input.output">issues</a> in [input.output].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The following member functions are declared const, yet return non-const -pointers. We believe they are should be changed, because they allow code -that may surprise the user. See document N1360 for details and -rationale. -</p> - -<p><i>[Santa Cruz: the real issue is that we've got const member -functions that return pointers to non-const, and N1360 proposes -replacing them by overloaded pairs. There isn't a consensus about -whether this is a real issue, since we've never said what our -constness policy is for iostreams. N1360 relies on a distinction -between physical constness and logical constness; that distinction, or -those terms, does not appear in the standard.]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p>In 27.4.4 and 27.4.4.2</p> -<p>Replace</p> -<pre> - basic_ostream<charT,traits>* tie() const; -</pre> -<p>with</p> -<pre> - basic_ostream<charT,traits>* tie(); - const basic_ostream<charT,traits>* tie() const; -</pre> - -<p>and replace</p> -<pre> - basic_streambuf<charT,traits>* rdbuf() const; -</pre> -<p>with</p> -<pre> - basic_streambuf<charT,traits>* rdbuf(); - const basic_streambuf<charT,traits>* rdbuf() const; -</pre> - -<p>In 27.5.2 and 27.5.2.3.1</p> -<p>Replace</p> -<pre> - char_type* eback() const; -</pre> -<p>with</p> -<pre> - char_type* eback(); - const char_type* eback() const; -</pre> - -<p>Replace</p> -<pre> - char_type gptr() const; -</pre> -<p>with</p> -<pre> - char_type* gptr(); - const char_type* gptr() const; -</pre> - -<p>Replace</p> -<pre> - char_type* egptr() const; -</pre> -<p>with</p> -<pre> - char_type* egptr(); - const char_type* egptr() const; -</pre> - -<p>In 27.5.2 and 27.5.2.3.2</p> -<p>Replace</p> -<pre> - char_type* pbase() const; -</pre> -<p>with</p> -<pre> - char_type* pbase(); - const char_type* pbase() const; -</pre> - -<p>Replace</p> -<pre> - char_type* pptr() const; -</pre> -<p>with</p> -<pre> - char_type* pptr(); - const char_type* pptr() const; -</pre> - -<p>Replace</p> -<pre> - char_type* epptr() const; -</pre> -<p>with</p> -<pre> - char_type* epptr(); - const char_type* epptr() const; -</pre> - -<p>In 27.7.2, 27.7.2.2, 27.7.3 27.7.3.2, 27.7.4, and 27.7.6</p> -<p>Replace</p> -<pre> - basic_stringbuf<charT,traits,Allocator>* rdbuf() const; -</pre> -<p>with</p> -<pre> - basic_stringbuf<charT,traits,Allocator>* rdbuf(); - const basic_stringbuf<charT,traits,Allocator>* rdbuf() const; -</pre> - -<p>In 27.8.1.5, 27.8.1.7, 27.8.1.8, 27.8.1.10, 27.8.1.11, and 27.8.1.13</p> -<p>Replace</p> -<pre> - basic_filebuf<charT,traits>* rdbuf() const; -</pre> -<p>with</p> -<pre> - basic_filebuf<charT,traits>* rdbuf(); - const basic_filebuf<charT,traits>* rdbuf() const; -</pre> - - -<p><b>Rationale:</b></p> -<p>The existing specification is a bit sloppy, but there's no - particular reason to change this other than tidiness, and there are - a number of ways in which streams might have been designed - differently if we were starting today. There's no evidence that the - existing constness policy is harming users. We might consider - a different constness policy as part of a full stream redesign.</p> - - - - - -<hr> -<h3><a name="367"></a>367. remove_copy/remove_copy_if and Input Iterators</h3> -<p><b>Section:</b> 25.3.8 [alg.remove] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Anthony Williams <b>Opened:</b> 2002-05-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.remove">issues</a> in [alg.remove].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -remove_copy and remove_copy_if (25.3.8 [alg.remove]) permit their -input range to be marked with Input Iterators. However, since two -operations are required against the elements to copy (comparison and -assigment), when the input range uses Input Iterators, a temporary -copy must be taken to avoid dereferencing the iterator twice. This -therefore requires the value type of the InputIterator to be -CopyConstructible. If the iterators are at least Forward Iterators, -then the iterator can be dereferenced twice, or a reference to the -result maintained, so the temporary is not required. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add "If InputIterator does not meet the requirements of forward -iterator, then the value type of InputIterator must be copy -constructible. Otherwise copy constructible is not required." to -25.3.8 [alg.remove] paragraph 6. -</p> - - -<p><b>Rationale:</b></p> -<p>The assumption is that an input iterator can't be dereferenced - twice. There's no basis for that assumption in the Standard.</p> - - - - - -<hr> -<h3><a name="368"></a>368. basic_string::replace has two "Throws" paragraphs</h3> -<p><b>Section:</b> 21.4.6.6 [string::replace] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2002-06-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string::replace">issues</a> in [string::replace].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -21.4.6.6 [string::replace] basic_string::replace, second -signature, given in paragraph 1, has two "Throws" paragraphs (3 and -5). -</p> - -<p> -In addition, the second "Throws" paragraph (5) includes specification -(beginning with "Otherwise, the function replaces ...") that should be -part of the "Effects" paragraph. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>This is editorial. Both "throws" statements are true. The bug is - just that the second one should be a sentence, part of the "Effects" - clause, not a separate "Throws". The project editor has been - notified.</p> - - - - - -<hr> -<h3><a name="372"></a>372. Inconsistent description of stdlib exceptions</h3> -<p><b>Section:</b> 17.6.5.12 [res.on.exception.handling], 18.7.1 [type.info] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Randy Maddox <b>Opened:</b> 2002-07-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#res.on.exception.handling">issues</a> in [res.on.exception.handling].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p>Paragraph 3 under clause 17.6.5.12 [res.on.exception.handling], Restrictions on -Exception Handling, states that "Any other functions defined in the -C++ Standard Library that do not have an exception-specification may -throw implementation-defined exceptions unless otherwise specified." -This statement is followed by a reference to footnote 178 at the -bottom of that page which states, apparently in reference to the C++ -Standard Library, that "Library implementations are encouraged (but -not required) to report errors by throwing exceptions from (or derived -from) the standard exceptions."</p> - -<p>These statements appear to be in direct contradiction to clause -18.7.1 [type.info], which states "The class exception defines the -base class for the types of objects thrown as exceptions by the C++ -Standard library components ...".</p> - -<p>Is this inconsistent?</p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>Clause 17 is setting the overall library requirements, and it's - clear and consistent. This sentence from Clause 18 is descriptive, - not setting a requirement on any other class. -</p> - - - - - -<hr> -<h3><a name="374"></a>374. moneypunct::frac_digits returns int not unsigned</h3> -<p><b>Section:</b> 22.4.6.3.1 [locale.moneypunct.members], 22.4.6.3.2 [locale.moneypunct.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Ray Lischner <b>Opened:</b> 2002-08-08 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In section 22.4.6.3.1 [locale.moneypunct.members], frac_digits() returns type -"int". This implies that frac_digits() might return a negative value, -but a negative value is nonsensical. It should return "unsigned". -</p> - -<p> -Similarly, in section 22.4.6.3.2 [locale.moneypunct.virtuals], do_frac_digits() -should return "unsigned". -</p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>Regardless of whether the return value is int or unsigned, it's -always conceivable that frac_digits might return a nonsensical -value. (Is 4294967295 really any better than -1?) The clients of -moneypunct, the get and put facets, can and do perform range -checks.</p> - - - - - -<hr> -<h3><a name="377"></a>377. basic_string::insert and length_error</h3> -<p><b>Section:</b> 21.4.6.4 [string::insert] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Ray Lischner <b>Opened:</b> 2002-08-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string::insert">issues</a> in [string::insert].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Section 21.4.6.4 [string::insert], paragraph 4, contains the following, -"Then throws length_error if size() >= npos - rlen." -</p> - -<p> -Related to DR 83, this sentence should probably be removed. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p><p>This requirement is redundant but correct. No change is -needed.</p> - - - - -<hr> -<h3><a name="378"></a>378. locale immutability and locale::operator=()</h3> -<p><b>Section:</b> 22.3.1 [locale] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2002-09-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale">issues</a> in [locale].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#31">31</a></p> -<p><b>Discussion:</b></p> -<p> -I think there is a problem with 22.1.1, p6 which says that -</p> -<pre> - -6- An instance of locale is immutable; once a facet reference - is obtained from it, that reference remains usable as long - as the locale value itself exists. -</pre> -<p> -and 22.1.1.2, p4: -</p> -<pre> - const locale& operator=(const locale& other) throw(); - - -4- Effects: Creates a copy of other, replacing the current value. -</pre> -<p> -How can a reference to a facet obtained from a locale object remain -valid after an assignment that clearly must replace all the facets -in the locale object? Imagine a program such as this -</p> -<pre> - std::locale loc ("de_DE"); - const std::ctype<char> &r0 = std::use_facet<std::ctype<char> >(loc); - loc = std::locale ("en_US"); - const std::ctype<char> &r1 = std::use_facet<std::ctype<char> >(loc); -</pre> -<p> -Is r0 really supposed to be preserved and destroyed only when loc goes -out of scope? -</p> - - -<p><b>Proposed resolution:</b></p> -<p><i>[Summer '04 mid-meeting mailing: Martin and Dietmar believe this - is a duplicate of issue <a href="lwg-defects.html#31">31</a> and recommend that it be - closed. -]</i></p> - - - - - - -<hr> -<h3><a name="382"></a>382. codecvt do_in/out result</h3> -<p><b>Section:</b> 22.4.1.4 [locale.codecvt] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2002-08-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt">issues</a> in [locale.codecvt].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -It seems that the descriptions of codecvt do_in() and do_out() leave -sufficient room for interpretation so that two implementations of -codecvt may not work correctly with the same filebuf. Specifically, -the following seems less than adequately specified: -</p> - -<ol> -<li> - the conditions under which the functions terminate -</li> -<li> - precisely when the functions return ok -</li> -<li> - precisely when the functions return partial -</li> -<li> - the full set of conditions when the functions return error -</li> -</ol> - -<ol> -<li> - 22.4.1.4.2 [locale.codecvt.virtuals], p2 says this about the effects of the - function: ...Stops if it encounters a character it cannot - convert... This assumes that there *is* a character to - convert. What happens when there is a sequence that doesn't form a - valid source character, such as an unassigned or invalid UNICODE - character, or a sequence that cannot possibly form a character - (e.g., the sequence "\xc0\xff" in UTF-8)? -</li> -<li> - Table 53 says that the function returns codecvt_base::ok - to indicate that the function(s) "completed the conversion." - Suppose that the source sequence is "\xc0\x80" in UTF-8, - with from pointing to '\xc0' and (from_end==from + 1). - It is not clear whether the return value should be ok - or partial (see below). -</li> -<li> - Table 53 says that the function returns codecvt_base::partial - if "not all source characters converted." With the from pointers - set up the same way as above, it is not clear whether the return - value should be partial or ok (see above). -</li> -<li> - Table 53, in the row describing the meaning of error mistakenly - refers to a "from_type" character, without the symbol from_type - having been defined. Most likely, the word "source" character - is intended, although that is not sufficient. The functions - may also fail when they encounter an invalid source sequence - that cannot possibly form a valid source character (e.g., as - explained in bullet 1 above). -</li> -</ol> -<p> -Finally, the conditions described at the end of 22.4.1.4.2 [locale.codecvt.virtuals], p4 don't seem to be possible: -</p> -<blockquote><p> - "A return value of partial, if (from_next == from_end), - indicates that either the destination sequence has not - absorbed all the available destination elements, or that - additional source elements are needed before another - destination element can be produced." -</p></blockquote> -<p> -If the value is partial, it's not clear to me that (from_next -==from_end) could ever hold if there isn't enough room -in the destination buffer. In order for (from_next==from_end) to -hold, all characters in that range must have been successfully -converted (according to 22.4.1.4.2 [locale.codecvt.virtuals], p2) and since there are no -further source characters to convert, no more room in the -destination buffer can be needed. -</p> -<p> -It's also not clear to me that (from_next==from_end) could ever -hold if additional source elements are needed to produce another -destination character (not element as incorrectly stated in the -text). partial is returned if "not all source characters have -been converted" according to Table 53, which also implies that -(from_next==from) does NOT hold. -</p> -<p> -Could it be that the intended qualifying condition was actually -(from_next != from_end), i.e., that the sentence was supposed -to read -</p> -<blockquote><p> - "A return value of partial, if (from_next != from_end),..." -</p></blockquote> -<p> -which would make perfect sense, since, as far as I understand it, -partial can only occur if (from_next != from_end)? -</p> -<p><i>[Lillehammer: Defer for the moment, but this really needs to be - fixed. Right now, the description of codecvt is too vague for it to - be a useful contract between providers and clients of codecvt - facets. (Note that both vendors and users can be both providers and - clients of codecvt facets.) The major philosophical issue is whether - the standard should only describe mappings that take a single wide - character to multiple narrow characters (and vice versa), or whether - it should describe fully general N-to-M conversions. When the - original standard was written only the former was contemplated, but - today, in light of the popularity of utf8 and utf16, that doesn't - seem sufficient for C++0x. Bill supports general N-to-M conversions; - we need to make sure Martin and Howard agree.]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -codecvt is meant to be a 1-to-N to N-to-1 conversion. It does not work -well for N-to-M conversions. wbuffer_convert now exists, and handles -N-to-M cases. Also, there is a new specialization of codecvt that -permits UTF-16 <-> UTF-8 conversions. -</p> -<p> -NAD without prejudice. Will reopen if proposed resolution is supplied. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - -<hr> -<h3><a name="385"></a>385. Does call by value imply the CopyConstructible requirement?</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2002-10-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Many function templates have parameters that are passed by value; -a typical example is <tt>find_if</tt>'s <i>pred</i> parameter in -25.2.5 [alg.find]. Are the corresponding template parameters -(<tt>Predicate</tt> in this case) implicitly required to be -CopyConstructible, or does that need to be spelled out explicitly? -</p> - -<p> -This isn't quite as silly a question as it might seem to be at first -sight. If you call <tt>find_if</tt> in such a way that template -argument deduction applies, then of course you'll get call by value -and you need to provide a copy constructor. If you explicitly provide -the template arguments, however, you can force call by reference by -writing something like <tt>find_if<my_iterator, -my_predicate&></tt>. The question is whether implementation -are required to accept this, or whether this is ill-formed because -my_predicate& is not CopyConstructible. -</p> - -<p> -The scope of this problem, if it is a problem, is unknown. Function -object arguments to generic algorithms in clauses 25 [algorithms] -and 26 [numerics] are obvious examples. A review of the whole -library is necessary. -</p> -<p><i>[ -This is really two issues. First, predicates are typically passed by -value but we don't say they must be Copy Constructible. They should -be. Second: is specialization allowed to transform value arguments -into references? References aren't copy constructible, so this should -not be allowed. -]</i></p> - -<p><i>[ -2007-01-12, Howard: First, despite the note above, references <b>are</b> -copy constructible. They just aren't assignable. Second, this is very -closely related to <a href="lwg-defects.html#92">92</a> and should be consistent with that. -That issue already says that implementations are allowed to copy -function objects. If one passes in a reference, it is copyable, but -susceptible to slicing if one passes in a reference to a base. Third, -with rvalue reference in the language one only needs to satisfy -MoveConstructible to pass an rvalue "by value". Though the function -might still copy the function object internally (requiring -CopyConstructible). Finally (and fwiw), if we wanted to, it is easy to -code all of the std::algorithms such that they do not copy function -objects internally. One merely passes them by reference internally if -desired (this has been fully implemented and shipped for several years). - If this were mandated, it would reverse <a href="lwg-defects.html#92">92</a>, allowing -function objects to reliably maintain state. E.g. the example in <a href="lwg-defects.html#92">92</a> would reliably remove only the third element. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Recommend NAD. -</p> - - -<p><b>Rationale:</b></p> -<p> -Generic algorithms will be marked with concepts and these will imply a requirement -of MoveConstructible (not CopyConstructible). The signature of the function will -then precisely describe and enforce the precise requirements. -</p> - - - - - -<hr> -<h3><a name="388"></a>388. Use of <tt>complex</tt> as a key in associative containers</h3> -<p><b>Section:</b> 26.4 [complex.numbers] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Gabriel Dos Reis <b>Opened:</b> 2002-11-08 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#complex.numbers">active issues</a> in [complex.numbers].</p> -<p><b>View all other</b> <a href="lwg-index.html#complex.numbers">issues</a> in [complex.numbers].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Practice with <tt>std::complex<></tt> and the associative containers -occasionally reveals artificial and distracting issues with constructs -resembling: <tt>std::set<std::complex<double> > s;</tt> -</p> - -<p> -The main reason for the above to fail is the absence of an appropriate -definition for <tt>std::less<std::complex<T> ></tt>. That in turn comes from -the definition of the primary template <tt>std::less<></tt> in terms of -<tt>operator<</tt>. -</p> - -<p> -The usual argument goes as follows: Since there is no ordering over -the complex field compatible with field operations it makes little -sense to define a function <tt>operator<</tt> operating on the datatype -<tt>std::complex<T></tt>. That is fine. However, that reasoning does not carry -over to <tt>std::less<T></tt> which is used, among other things, by associative -containers as an ordering useful to meet complexity requirements. -</p> - -<p>Related issue: <a href="lwg-closed.html#348">348</a>.</p> - -<p><i>[ -Pre Bellevue: Reopened at the request of Alisdair. -]</i></p> - - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -This is a request for a design change, and not a defect in the standard. -It is in scope to consider, but the group feels that it is not a change -that we need to do. Is there a total ordering for floating point values, -including NaN? There is not a clear enough solution or big enough -problem for us to solve. Solving this problem would require solving the -problem for floating point, which is equally unclear. The LWG noted that -users who want to put objects into an associative container for which -<tt>operator<</tt> isn't defined can simply provide their own comparison -function object. NAD -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p>Informally: Add a specialization of <tt>std::less</tt> for <tt>std::complex</tt>.</p> - - -<p><b>Rationale:</b></p> -<p>Discussed in Santa Cruz. An overwhelming majority of the LWG -believes this should not be treated a DR: it's a request for a design -change, not a defect in the existing standard. Most people (10-3) -believed that we probably don't want this change, period: as with -issue <a href="lwg-closed.html#348">348</a>, it's hard to know where to draw the line. -The LWG noted that users who want to put objects into an associative -container for which <tt>operator<</tt> isn't defined can simply -provide their own comparison function object.</p> - - - - - -<hr> -<h3><a name="390"></a>390. CopyConstructible requirements too strict</h3> -<p><b>Section:</b> 17.6.3.1 [utility.arg.requirements] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Doug Gregor <b>Opened:</b> 2002-10-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#utility.arg.requirements">issues</a> in [utility.arg.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The CopyConstructible requirements in Table 30 state that for an -object t of type T (where T is CopyConstructible), the expression &t -returns the address of t (with type T*). This requirement is overly -strict, in that it disallows types that overload operator& to not -return a value of type T*. This occurs, for instance, in the <a -href="http://www.boost.org/libs/lambda">Boost.Lambda</a> library, where -operator& is overloaded for a Boost.Lambda function object to return -another function object. -</p> - -<p>Example:</p> - -<pre> - std::vector<int> u, v; - int x; - // ... - std::transform(u.begin(), u.end(), std::back_inserter(v), _1 * x); -</pre> - -<p> -_1 * x returns an unnamed function object with operator& overloaded to -not return T* , therefore rendering the std::transform call ill-formed. -However, most standard library implementations will compile this code -properly, and the viability of such binder libraries is severely hindered -by the unnecessary restriction in the CopyConstructible requirements. -</p> - -<p> -For reference, the address of an object can be retrieved without using -the address-of operator with the following function template: -</p> - -<pre> - template <typename T> T* addressof(T& v) - { - return reinterpret_cast<T*>( - &const_cast<char&>(reinterpret_cast<const volatile char &>(v))); - } -</pre> - -<p> -Note: this relates directly to library issue <a href="lwg-closed.html#350">350</a>, which -will need to be reexamined if the CopyConstructible requirements -change. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Remove the last two rows of Table 30, eliminating the requirements -that &t and &u return the address of t and u, respectively. -</p> - - -<p><b>Rationale:</b></p> -<p>This was a deliberate design decision. Perhaps it should be - reconsidered for C++0x. </p> - - - - - -<hr> -<h3><a name="392"></a>392. 'equivalence' for input iterators</h3> -<p><b>Section:</b> 24.2.3 [input.iterators] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Corwin Joy <b>Opened:</b> 2002-12-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#input.iterators">issues</a> in [input.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -In section 24.2.3 [input.iterators] table 72 - -'Input Iterator Requirements' we have as a postcondition of *a: -"If a==b and (a, b) is in the domain of == then *a is equivalent to *b". -</p> - -<p> -In section 24.6.3.5 [istreambuf.iterator::equal] it states that -"istreambuf_iterator::equal returns true if and only if both iterators -are at end-of-stream, or neither is at end-of-stream, <i>regardless of -what streambuf object they use</i>." (My emphasis). -</p> - -<p> -The defect is that either 'equivalent' needs to be more precisely -defined or the conditions for equality in 24.6.3.5 [istreambuf.iterator::equal] -are incorrect. (Or both). -</p> - -<p>Consider the following example:</p> -<pre> - #include <iostream> - #include <fstream> - #include <iterator> - using namespace std; - - int main() { - ifstream file1("file1.txt"), file2("file2.txt"); - istreambuf_iterator<char> f1(file1), f2(file2); - cout << "f1 == f2 : " << boolalpha << (f1 == f2) << endl; - cout << "f1 = " << *f1 << endl; - cout << "f2 = " << *f2 << endl; - return 0; - } -</pre> - -<p>Now assuming that neither f1 or f2 are at the end-of-stream then -f1 == f2 by 24.6.3.5 [istreambuf.iterator::equal].</p> - -<p>However, it is unlikely that *f1 will give the same value as *f2 except -by accident.</p> - -<p>So what does *f1 'equivalent' to *f2 mean? I think the standard should -be clearer on this point, or at least be explicit that this does not -mean that *f1 and *f2 are required to have the same value in the case -of input iterators.</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p><p>The two iterators aer not in the domain of ==</p> - - - - - - -<hr> -<h3><a name="393"></a>393. do_in/do_out operation on state unclear</h3> -<p><b>Section:</b> 22.4.1.4.2 [locale.codecvt.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alberto Barbati <b>Opened:</b> 2002-12-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt.virtuals">issues</a> in [locale.codecvt.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -this DR follows the discussion on the previous thread "codecvt::do_in -not consuming external characters". It's just a clarification issue -and not a request for a change. -</p> -<p> -Can do_in()/do_out() produce output characters without consuming input -characters as a result of operation on state? -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add a note at the end of 22.4.1.4.2 [locale.codecvt.virtuals], -paragraph 3: -</p> - -<p> -[Note: As a result of operations on state, it can return ok or partial -and set from_next == from and to_next != to. --end note] -</p> - - -<p><b>Rationale:</b></p> -<p> -The submitter believes that standard already provides an affirmative -answer to the question. However, the current wording has induced a few -library implementors to make the incorrect assumption that -do_in()/do_out() always consume at least one internal character when -they succeed. -</p> - -<p> -The submitter also believes that the proposed resolution is not in -conflict with the related issue 76. Moreover, by explicitly allowing -operations on state to produce characters, a codecvt implementation -may effectively implement N-to-M translations without violating the -"one character at a time" principle described in such issue. On a side -note, the footnote in the proposed resolution of issue 76 that -informally rules out N-to-M translations for basic_filebuf should be -removed if this issue is accepted as valid. -</p> - - -<p><i>[ -Kona (2007): The proposed resolution is to add a note. Since this is -non-normative, the issue is editorial, but we believe that the note is -correct. Proposed Disposition: NAD, Editorial -]</i></p> - - - - - - -<hr> -<h3><a name="394"></a>394. behavior of formatted output on failure</h3> -<p><b>Section:</b> 27.7.3.6.1 [ostream.formatted.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2002-12-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -There is a contradiction in Formatted output about what bit is -supposed to be set if the formatting fails. On sentence says it's -badbit and another that it's failbit. -</p> -<p> -27.6.2.5.1, p1 says in the Common Requirements on Formatted output -functions: -</p> -<pre> - ... If the generation fails, then the formatted output function - does setstate(ios::failbit), which might throw an exception. -</pre> -<p> -27.6.2.5.2, p1 goes on to say this about Arithmetic Inserters: -</p> -<p> - ... The formatting conversion occurs as if it performed the - following code fragment: -</p> -<pre> - bool failed = - use_facet<num_put<charT,ostreambuf_iterator<charT,traits> - > > - (getloc()).put(*this, *this, fill(), val). failed(); - - ... If failed is true then does setstate(badbit) ... -</pre> -<p> -The original intent of the text, according to Jerry Schwarz (see -c++std-lib-10500), is captured in the following paragraph: -</p> -<p> -In general "badbit" should mean that the stream is unusable because -of some underlying failure, such as disk full or socket closure; -"failbit" should mean that the requested formatting wasn't possible -because of some inconsistency such as negative widths. So typically -if you clear badbit and try to output something else you'll fail -again, but if you clear failbit and try to output something else -you'll succeed. -</p> -<p> -In the case of the arithmetic inserters, since num_put cannot -report failure by any means other than exceptions (in response -to which the stream must set badbit, which prevents the kind of -recoverable error reporting mentioned above), the only other -detectable failure is if the iterator returned from num_put -returns true from failed(). -</p> -<p> -Since that can only happen (at least with the required iostream -specializations) under such conditions as the underlying failure -referred to above (e.g., disk full), setting badbit would seem -to be the appropriate response (indeed, it is required in -27.6.2.5.2, p1). It follows that failbit can never be directly -set by the arithmetic (it can only be set by the sentry object -under some unspecified conditions). -</p> -<p> -The situation is different for other formatted output functions -which can fail as a result of the streambuf functions failing -(they may do so by means other than exceptions), and which are -then required to set failbit. -</p> -<p> -The contradiction, then, is that ostream::operator<<(int) will -set badbit if the disk is full, while operator<<(ostream&, -char) will set failbit under the same conditions. To make the behavior -consistent, the Common requirements sections for the Formatted output -functions should be changed as proposed below. -</p> -<p><i>[Kona: There's agreement that this is a real issue. What we - decided at Kona: 1. An error from the buffer (which can be detected - either directly from streambuf's member functions or by examining a - streambuf_iterator) should always result in badbit getting set. - 2. There should never be a circumstance where failbit gets set. - That represents a formatting error, and there are no circumstances - under which the output facets are specified as signaling a - formatting error. (Even more so for string output that for numeric - because there's nothing to format.) If we ever decide to make it - possible for formatting errors to exist then the facets can signal - the error directly, and that should go in clause 22, not clause 27. - 3. The phrase "if generation fails" is unclear and should be - eliminated. It's not clear whether it's intended to mean a buffer - error (e.g. a full disk), a formatting error, or something else. - Most people thought it was supposed to refer to buffer errors; if - so, we should say so. Martin will provide wording.]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -NAD. This issue is already fixed. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="397"></a>397. <tt>ostream::sentry</tt> dtor throws exceptions</h3> -<p><b>Section:</b> 27.7.3.4 [ostream::sentry] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2003-01-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ostream::sentry">issues</a> in [ostream::sentry].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - <p> -17.4.4.8, p3 prohibits library dtors from throwing exceptions. - </p> - <p> -27.6.2.3, p4 says this about the ostream::sentry dtor: - </p> - <pre> - -4- If ((os.flags() & ios_base::unitbuf) && !uncaught_exception()) - is true, calls os.flush(). - </pre> - <p> -27.6.2.6, p7 that describes ostream::flush() says: - </p> - <pre> - -7- If rdbuf() is not a null pointer, calls rdbuf()->pubsync(). - If that function returns ?-1 calls setstate(badbit) (which - may throw ios_base::failure (27.4.4.3)). - </pre> - <p> -That seems like a defect, since both pubsync() and setstate() can -throw an exception. - </p> -<p><i>[ -The contradiction is real. Clause 17 says destructors may never -throw exceptions, and clause 27 specifies a destructor that does -throw. In principle we might change either one. We're leaning -toward changing clause 17: putting in an "unless otherwise specified" -clause, and then putting in a footnote saying the sentry destructor -is the only one that can throw. PJP suggests specifying that -sentry::~sentry() should internally catch any exceptions it might cause. -]</i></p> - - -<p><i>[ -See <a href="lwg-closed.html#418">418</a> and <a href="lwg-defects.html#622">622</a> for related issues. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -Move to Review. Add "Throws: nothing" to the specification of <tt>ostream::sentry::~sentry()</tt>. -</p> -</blockquote> - -<p><i>[ -2009-10-13 Daniel adds: -]</i></p> - - -<blockquote><p> -The proposed resolution of <a href="lwg-defects.html#835">835</a> is written to match the outcome -of this issue. -</p></blockquote> - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote><p> -Move to Open. Our intent is to solve this issue with <a href="lwg-defects.html#835">835</a>. -</p></blockquote> - -<p><i>[ -2010-03-06 Martin updates wording. -]</i></p> - - -<p><i>[ -2010 Pittsburgh: -]</i></p> - - -<blockquote><p> -Moved to NAD Editorial. -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p> -Solved by <a href="lwg-defects.html#835">835</a>. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add after 27.7.3.4 [ostream::sentry] p17: -</p> - -<blockquote> -<pre> -~sentry(); -</pre> -<blockquote> -<p> --17- If <tt>(os.flags() & ios_base::unitbuf)</tt> -is <tt>true</tt>, calls <tt>os.flush()</tt>. -</p> - -<p><ins> -<i>Throws:</i> Nothing. -</ins></p> -</blockquote> -</blockquote> - - - - - -<hr> -<h3><a name="398"></a>398. effects of end-of-file on unformatted input functions</h3> -<p><b>Section:</b> 27.7.3.4 [ostream::sentry] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2003-01-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ostream::sentry">issues</a> in [ostream::sentry].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - <p> -While reviewing unformatted input member functions of istream -for their behavior when they encounter end-of-file during input -I found that the requirements vary, sometimes unexpectedly, and -in more than one case even contradict established practice (GNU -libstdc++ 3.2, IBM VAC++ 6.0, STLPort 4.5, SunPro 5.3, HP aCC -5.38, Rogue Wave libstd 3.1, and Classic Iostreams). - </p> - <p> -The following unformatted input member functions set eofbit if they -encounter an end-of-file (this is the expected behavior, and also -the behavior of all major implementations): - </p> - <pre> - basic_istream<charT, traits>& - get (char_type*, streamsize, char_type); - </pre> - <p> - Also sets failbit if it fails to extract any characters. - </p> - <pre> - basic_istream<charT, traits>& - get (char_type*, streamsize); - </pre> - <p> - Also sets failbit if it fails to extract any characters. - </p> - <pre> - basic_istream<charT, traits>& - getline (char_type*, streamsize, char_type); - </pre> - <p> - Also sets failbit if it fails to extract any characters. - </p> - <pre> - basic_istream<charT, traits>& - getline (char_type*, streamsize); - </pre> - <p> - Also sets failbit if it fails to extract any characters. - </p> - <pre> - basic_istream<charT, traits>& - ignore (int, int_type); - </pre> - <pre> - basic_istream<charT, traits>& - read (char_type*, streamsize); - </pre> - <p> - Also sets failbit if it encounters end-of-file. - </p> - <pre> - streamsize readsome (char_type*, streamsize); - </pre> - - <p> -The following unformated input member functions set failbit but -not eofbit if they encounter an end-of-file (I find this odd -since the functions make it impossible to distinguish a general -failure from a failure due to end-of-file; the requirement is -also in conflict with all major implementation which set both -eofbit and failbit): - </p> - <pre> - int_type get(); - </pre> - <pre> - basic_istream<charT, traits>& - get (char_type&); - </pre> - <p> -These functions only set failbit of they extract no characters, -otherwise they don't set any bits, even on failure (I find this -inconsistency quite unexpected; the requirement is also in -conflict with all major implementations which set eofbit -whenever they encounter end-of-file): - </p> - <pre> - basic_istream<charT, traits>& - get (basic_streambuf<charT, traits>&, char_type); - </pre> - <pre> - basic_istream<charT, traits>& - get (basic_streambuf<charT, traits>&); - </pre> - <p> -This function sets no bits (all implementations except for -STLport and Classic Iostreams set eofbit when they encounter -end-of-file): - </p> - <pre> - int_type peek (); - </pre> -<p>Informally, what we want is a global statement of intent saying - that eofbit gets set if we trip across EOF, and then we can take - away the specific wording for individual functions. A full review - is necessary. The wording currently in the standard is a mishmash, - and changing it on an individual basis wouldn't make things better. - Dietmar will do this work.</p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Moved to NAD. See 27.7.2.1 [istream] p3. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - -<hr> -<h3><a name="399"></a>399. volations of unformatted input function requirements</h3> -<p><b>Section:</b> 27.7.2.3 [istream.unformatted] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2003-01-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#istream.unformatted">active issues</a> in [istream.unformatted].</p> -<p><b>View all other</b> <a href="lwg-index.html#istream.unformatted">issues</a> in [istream.unformatted].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - <p> -The Effects clauses for the two functions below violate the -general requirements on unformatted input functions outlined -in 27.6.1.3: they do not begin by constructing a sentry object. -Instead, they begin by calling widen ('\n'), which may throw -an exception. The exception is then allowed to propagate from -the unformatted input function irrespective of the setting of -exceptions(). - </p> - <p> -Note that in light of 27.6.1.1, p3 and p4, the fact that the -functions allow exceptions thrown from widen() to propagate -may not strictly speaking be a defect (but the fact that the -functions do not start by constructing a sentry object still -is). However, since an exception thrown from ctype<charT> -::widen() during any other input operation (say, from within -a call to num_get<charT>::get()) will be caught and cause -badbit to be set, these two functions should not be treated -differently for the sake of consistency. - </p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p> -Not a defect. The standard is consistent, and the behavior required -by the standard is unambiguous. Yes, it's theoretically possible for -widen to throw. (Not that this will happen for the default ctype -facet or for most real-world replacement ctype facets.) Users who -define ctype facets that can throw, and who care about this behavior, -can use alternative signatures that don't call widen. -</p> - - - - - - -<hr> -<h3><a name="408"></a>408. Is <tt>vector<reverse_iterator<char*> ></tt> forbidden?</h3> -<p><b>Section:</b> 24.2 [iterator.requirements] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Nathan Myers <b>Opened:</b> 2003-06-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iterator.requirements">issues</a> in [iterator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I've been discussing iterator semantics with Dave Abrahams, and a -surprise has popped up. I don't think this has been discussed before. -</p> - -<p> -X [iterator.concepts] says that the only operation that can be performed on "singular" -iterator values is to assign a non-singular value to them. (It -doesn't say they can be destroyed, and that's probably a defect.) -Some implementations have taken this to imply that there is no need -to initialize the data member of a <tt>reverse_iterator<></tt> in the default -constructor. As a result, code like -</p> -<blockquote><pre> - std::vector<std::reverse_iterator<char*> > v(7); - v.reserve(1000); -</pre></blockquote> -<p> -invokes undefined behavior, because it must default-initialize the -vector elements, and then copy them to other storage. Of course many -other vector operations on these adapters are also left undefined, -and which those are is not reliably deducible from the standard. -</p> - -<p> -I don't think that 24.1 was meant to make standard-library iterator -types unsafe. Rather, it was meant to restrict what operations may -be performed by functions which take general user- and standard -iterators as arguments, so that raw pointers would qualify as -iterators. However, this is not clear in the text, others have come -to the opposite conclusion. -</p> - -<p> -One question is whether the standard iterator adaptors have defined -copy semantics. Another is whether they have defined destructor -semantics: is -</p> -<blockquote><pre> - { std::vector<std::reverse_iterator<char*> > v(7); } -</pre></blockquote> -<p> -undefined too? -</p> - -<p> -Note this is not a question of whether algorithms are allowed to -rely on copy semantics for arbitrary iterators, just whether the -types we actually supply support those operations. I believe the -resolution must be expressed in terms of the semantics of the -adapter's argument type. It should make clear that, e.g., the -<tt>reverse_iterator<T></tt> constructor is actually required to execute -<tt>T()</tt>, and so copying is defined if the result of <tt>T()</tt> is copyable. -</p> - -<p> -Issue <a href="lwg-defects.html#235">235</a>, which defines <tt>reverse_iterator</tt>'s default -constructor more precisely, has some relevance to this issue. -However, it is not the whole story. -</p> - -<p> -The issue was whether -</p> -<blockquote><pre> - reverse_iterator() { } -</pre></blockquote> -<p> -is allowed, vs. -</p> -<blockquote><pre> - reverse_iterator() : current() { } -</pre></blockquote> - -<p> -The difference is when <tt>T</tt> is <tt>char*</tt>, where the first leaves the member -uninitialized, and possibly equal to an existing pointer value, or -(on some targets) may result in a hardware trap when copied. -</p> - -<p> -8.5 paragraph 5 seems to make clear that the second is required to -satisfy DR <a href="lwg-defects.html#235">235</a>, at least for non-class Iterator argument -types. -</p> - -<p> -But that only takes care of <tt>reverse_iterator</tt>, and doesn't establish -a policy for all iterators. (The reverse iterator adapter was just -an example.) In particular, does my function -</p> -<blockquote><pre> - template <typename Iterator> - void f() { std::vector<Iterator> v(7); } -</pre></blockquote> -<p> -evoke undefined behavior for some conforming iterator definitions? -I think it does, now, because <tt>vector<></tt> will destroy those singular -iterator values, and that's explicitly disallowed. -</p> - -<p> -24.1 shouldn't give blanket permission to copy all singular iterators, -because then pointers wouldn't qualify as iterators. However, it -should allow copying of that subset of singular iterator values that -are default-initialized, and it should explicitly allow destroying any -iterator value, singular or not, default-initialized or not. -</p> - -<p>Related issues: <a href="lwg-defects.html#407">407</a>, <a href="lwg-defects.html#1012">1012</a></p> -<p><i>[ -We don't want to require all singular iterators to be copyable, -because that is not the case for pointers. However, default -construction may be a special case. Issue: is it really default -construction we want to talk about, or is it something like value -initialization? We need to check with core to see whether default -constructed pointers are required to be copyable; if not, it would be -wrong to impose so strict a requirement for iterators. -]</i></p> - - -<p><i>[ -2009-05-10 Alisdair provided wording. -]</i></p> - - -<blockquote><p> -The comments regarding destroying singular iterators have already been -resolved. That just leaves copying (with moving implied). -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -This is related to LWG <a href="lwg-defects.html#1012">1012</a>. -</p> -<p> -Note that there is a bug in the proposed resolution to LWG <a href="lwg-defects.html#1012">1012</a>. The -change to [reverse.iter.con] should be modified so that the word -"default" in the second sentence of the Effects clause is replaced by -"value." -</p> -<p> -We believe that the proposed fix to LWG <a href="lwg-defects.html#1012">1012</a> (now corrected) is -sufficient to solve the problem for reverse_iterator. However, Alisdair -pointed out that LWG <a href="lwg-defects.html#1012">1012</a> does not solve the general problem for authors -of iterator adaptors. -</p> -<p> -There are some problems with the proposed resolution. The phrase "safely -copyable" is not a term of art. Also, it mentions a -DefaultConstructible? concept. -</p> -<p> -Move to Review after Alisdair updates the wording. -</p> -</blockquote> - -<p><i>[ -2009-07-31 Alisdair revised wording: -]</i></p> - - -<p><i>[ -2009-08-17 Alisdair and Daniel collaborate on slightly revised wording. -This issue depends upon <a href="lwg-defects.html#724">724</a> -]</i></p> - - -<p><i>[ -2009-10-14 Daniel adds: -]</i></p> - - -<blockquote><p> -There is a clear dependency on <a href="lwg-active.html#1213">1213</a>, because the term "singular", -which is used as part of the resolution, is not properly defined yet. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Moved to Open. Alisdair will provide improved wording to make -this have "value semantics" and otherwise behave like a valid iterator. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -Solved by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3066.html">N3066</a>. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add a new paragrpah to Iterator concepts 24.2 [iterator.requirements] after para 5 (the one describing -singular iterators) -</p> -<blockquote> -<p> -Just as a regular pointer to an array guarantees that there is a pointer -value pointing past the last element of the array, so for any iterator -type there is an iterator value that points past the last element of a -corresponding container. These values are called <i>past-the-end</i> values. -Values of an iterator <tt>i</tt> for which the expression <tt>*i</tt> is defined are called -<i>dereferenceable</i>. The library never assumes that past-the-end values are -dereferenceable. Iterators can also have singular values that are not -associated with any container. [<i>Example:</i> After the declaration of an -uninitialized pointer <tt>x</tt> (as with <tt>int* x;</tt>), <tt>x</tt> must always be assumed to -have a singular value of a pointer. — <i>end example</i>] Results of most -expressions are undefined for singular values; the only exceptions are -destroying an iterator that holds a singular value and the assignment of -a non-singular value to an iterator that holds a singular value. In this -case the singular value is overwritten the same way as any other value. -Dereferenceable values are always non-singular. -</p> -<p><ins> -After value-initialization, any iterator that satisfies the -<tt>DefaultConstructible</tt> requirements ([defaultconstructible]) shall not introduce undefined behaviour -when used <ins>as</ins> the -source of a copy or move operation, even if it would -otherwise be singular. [<i>Note:</i> This guarantee is not offered for -default-initialization (8.5 [dcl.init]), although the distinction only -matters for types with trivial default constructors such as pointers. — -<i>end note</i>] -</ins></p> - - -</blockquote> - - - - - - -<hr> -<h3><a name="417"></a>417. what does <tt>ctype::do_widen()</tt> return on failure</h3> -<p><b>Section:</b> 22.4.1.1.2 [locale.ctype.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2003-09-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.ctype.virtuals">issues</a> in [locale.ctype.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The Effects and Returns clauses of the <tt>do_widen()</tt> member function of -the <tt>ctype</tt> facet fail to specify the behavior of the function on failure. -That the function may not be able to simply cast the narrow character -argument to the type of the result since doing so may yield the wrong value -for some <tt>wchar_t</tt> encodings. Popular implementations of <tt>ctype<wchar_t></tt> that -use <tt>mbtowc()</tt> and UTF-8 as the native encoding (e.g., GNU glibc) will fail -when the argument's MSB is set. There is no way for the the rest of locale -and iostream to reliably detect this failure. -</p> -<p><i>[Kona: This is a real problem. Widening can fail. It's unclear - what the solution should be. Returning <tt>WEOF</tt> works for the <tt>wchar_t</tt> - specialization, but not in general. One option might be to add a - default, like <i>narrow</i>. But that's an incompatible change. - Using <i>traits::eof</i> might seem like a good idea, but facets - don't have access to traits (a recurring problem). We could - have <i>widen</i> throw an exception, but that's a scary option; - existing library components aren't written with the assumption - that <i>widen</i> can throw.]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -NAD. The behavior is specified for all of the facets that an -implementation is required to provide, for the basic character set. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - -<hr> -<h3><a name="418"></a>418. exceptions thrown during iostream cleanup</h3> -<p><b>Section:</b> 27.5.3.1.6 [ios::Init] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2003-09-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ios::Init">issues</a> in [ios::Init].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The dtor of the <tt>ios_base::Init</tt> object is supposed to call <tt>flush()</tt> on the -6 standard iostream objects <tt>cout</tt>, <tt>cerr</tt>, <tt>clog</tt>, <tt>wcout</tt>, -<tt>wcerr</tt>, and <tt>wclog</tt>. -This call may cause an exception to be thrown. -</p> - -<p> -17.4.4.8, p3 prohibits all library destructors from throwing exceptions. -</p> - -<p> -The question is: What should this dtor do if one or more of these calls -to <tt>flush()</tt> ends up throwing an exception? This can happen quite easily -if one of the facets installed in the locale imbued in the iostream -object throws. -</p> -<p><i>[Kona: We probably can't do much better than what we've got, so - the LWG is leaning toward NAD. At the point where the standard - stream objects are being cleaned up, the usual error reporting - mechanism are all unavailable. And exception from <tt>flush</tt> at this - point will definitely cause problems. A quality implementation - might reasonably swallow the exception, or call <tt>abort</tt>, or do - something even more drastic.]</i></p> - - -<p><i>[ -See <a href="lwg-closed.html#397">397</a> and <a href="lwg-defects.html#622">622</a> for related issues. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Moved to NAD, no consensus for change. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - -<hr> -<h3><a name="421"></a>421. is <tt>basic_streambuf</tt> copy-constructible?</h3> -<p><b>Section:</b> 27.6.3.1 [streambuf.cons] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2003-09-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#streambuf.cons">issues</a> in [streambuf.cons].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The reflector thread starting with c++std-lib-11346 notes that the class -template <tt>basic_streambuf</tt>, along with <tt>basic_stringbuf</tt> and <tt>basic_filebuf</tt>, -is copy-constructible but that the semantics of the copy constructors -are not defined anywhere. Further, different implementations behave -differently in this respect: some prevent copy construction of objects -of these types by declaring their copy ctors and assignment operators -private, others exhibit undefined behavior, while others still give -these operations well-defined semantics. -</p> - -<p> -Note that this problem doesn't seem to be isolated to just the three -types mentioned above. A number of other types in the library section -of the standard provide a compiler-generated copy ctor and assignment -operator yet fail to specify their semantics. It's believed that the -only types for which this is actually a problem (i.e. types where the -compiler-generated default may be inappropriate and may not have been -intended) are locale facets. See issue <a href="lwg-closed.html#439">439</a>. -</p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -NAD. Option B is already in the Working Draft. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -27.5.2 [lib.streambuf]: Add into the synopsis, public section, just above the destructor declaration: -</p> - -<blockquote> -<pre> -basic_streambuf(const basic_streambuf& sb); -basic_streambuf& operator=(const basic_streambuf& sb); -</pre> -</blockquote> - -<p>Insert after 27.5.2.1, paragraph 2:</p> -<blockquote> -<pre> -basic_streambuf(const basic_streambuf& sb); -</pre> - -<p>Constructs a copy of <tt>sb</tt>.</p> -<p>Postcondtions:</p> -<pre> - eback() == sb.eback() - gptr() == sb.gptr() - egptr() == sb.egptr() - pbase() == sb.pbase() - pptr() == sb.pptr() - epptr() == sb.epptr() - getloc() == sb.getloc() -</pre> - -<pre> -basic_streambuf& operator=(const basic_streambuf& sb); -</pre> - -<p>Assigns the data members of <tt>sb</tt> to this.</p> - -<p>Postcondtions:</p> -<pre> - eback() == sb.eback() - gptr() == sb.gptr() - egptr() == sb.egptr() - pbase() == sb.pbase() - pptr() == sb.pptr() - epptr() == sb.epptr() - getloc() == sb.getloc() -</pre> - -<p>Returns: *this.</p> -</blockquote> - -<p>27.7.1 [lib.stringbuf]:</p> - -<p><b>Option A:</b></p> - -<blockquote> -<p>Insert into the <tt>basic_stringbuf</tt> synopsis in the private section:</p> - -<pre> -basic_stringbuf(const basic_stringbuf&); // not defined -basic_stringbuf& operator=(const basic_stringbuf&); // not defined -</pre> -</blockquote> - -<p><b>Option B:</b></p> - -<blockquote> -<p>Insert into the <tt>basic_stringbuf</tt> synopsis in the public section:</p> - -<pre> -basic_stringbuf(const basic_stringbuf& sb); -basic_stringbuf& operator=(const basic_stringbuf& sb); -</pre> - -<p>27.7.1.1, insert after paragraph 4:</p> - -<pre>basic_stringbuf(const basic_stringbuf& sb);</pre> - -<p> -Constructs an independent copy of <tt>sb</tt> as if with <tt>sb.str()</tt>, and with the openmode that <tt>sb</tt> was constructed with. -</p> - -<p>Postcondtions: </p> -<pre> - str() == sb.str() - gptr() - eback() == sb.gptr() - sb.eback() - egptr() - eback() == sb.egptr() - sb.eback() - pptr() - pbase() == sb.pptr() - sb.pbase() - getloc() == sb.getloc() -</pre> - -<p> -Note: The only requirement on <tt>epptr()</tt> is that it point beyond the initialized range if an -output sequence exists. There is no requirement that <tt>epptr() - pbase() == sb.epptr() - sb.pbase()</tt>. -</p> - -<pre>basic_stringbuf& operator=(const basic_stringbuf& sb);</pre> -<p> -After assignment the <tt>basic_stringbuf</tt> has the same state as if it were initially copy constructed -from <tt>sb</tt>, except that the <tt>basic_stringbuf</tt> is allowed to retain any excess capacity it -might have, which may in turn effect the value of <tt>epptr()</tt>. -</p> -</blockquote> - -<p>27.8.1.1 [lib.filebuf]</p> - -<p>Insert at the bottom of the <tt>basic_filebuf</tt> synopsis:</p> - -<blockquote> -<pre> -private: - basic_filebuf(const basic_filebuf&); // not defined - basic_filebuf& operator=(const basic_filebuf&); // not defined -</pre> -</blockquote> -<p><i>[Kona: this is an issue for <tt>basic_streambuf</tt> itself and for its - derived classes. We are leaning toward allowing <tt>basic_streambuf</tt> to - be copyable, and specifying its precise semantics. (Probably the - obvious: copying the buffer pointers.) We are less sure whether - the <tt>streambuf</tt> derived classes should be copyable. Howard will - write up a proposal.]</i></p> - - -<p><i>[Sydney: Dietmar presented a new argument against <tt>basic_streambuf</tt> - being copyable: it can lead to an encapsulation violation. <tt>filebuf</tt> - inherits from <tt>streambuf</tt>. Now suppose you inherit a <tt>my_hijacking_buf</tt> - from <tt>streambuf</tt>. You can copy the <tt>streambuf</tt> portion of a <tt>filebuf</tt> to a - <tt>my_hijacking_buf</tt>, giving you access to the pointers into the - <tt>filebuf</tt>'s internal buffer. Perhaps not a very strong argument, but - it was strong enough to make people nervous. There was weak - preference for having <tt>streambuf</tt> not be copyable. There was weak - preference for having <tt>stringbuf</tt> not be copyable even if <tt>streambuf</tt> - is. Move this issue to open for now. -]</i></p> - - -<p><i>[ -2007-01-12, Howard: -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1862.html#27.5.2%20-%20Class%20template%20basic_streambuf%3CcharT,traits%3E">Rvalue Reference Recommendations for Chapter 27</a> -recommends protected copy constructor and assignment for <tt>basic_streambuf</tt> with the same semantics -as would be generated by the compiler. These members aid in derived classes implementing move semantics. -A protected copy constructor and copy assignment operator do not expose encapsulation more so than it is -today as each data member of a <tt>basic_streambuf</tt> is already both readable and writable by derived -classes via various get/set protected member functions (<tt>eback()</tt>, <tt>setp()</tt>, etc.). Rather -a protected copy constructor and copy assignment operator simply make the job of derived classes implementing -move semantics less tedious and error prone. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -27.5.2 [lib.streambuf]: The proposed <tt>basic_streambuf</tt> copy constructor -and assignment operator are the same as currently implied by the lack -of declarations: public and simply copies the data members. This -resolution is not a change but a clarification of the current -standard. -</p> - -<p> -27.7.1 [lib.stringbuf]: There are two reasonable options: A) Make -<tt>basic_stringbuf</tt> not copyable. This is likely the status-quo of -current implementations. B) Reasonable copy semantics of -<tt>basic_stringbuf</tt> can be defined and implemented. A copyable -<tt>basic_streambuf</tt> is arguably more useful than a non-copyable one. This -should be considered as new functionality and not the fixing of a -defect. If option B is chosen, ramifications from issue 432 are taken -into account. -</p> - -<p> -27.8.1.1 [lib.filebuf]: There are no reasonable copy semantics for -<tt>basic_filebuf</tt>. -</p> - - - - - - -<hr> -<h3><a name="424"></a>424. normative notes</h3> -<p><b>Section:</b> 17.5.1.2 [structure.summary] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2003-09-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -The text in 17.3.1.1, p1 says: -<br/> - -"Paragraphs labelled "Note(s):" or "Example(s):" are informative, other -paragraphs are normative." -<br/> - -The library section makes heavy use of paragraphs labeled "Notes(s)," -some of which are clearly intended to be normative (see list 1), while -some others are not (see list 2). There are also those where the intent -is not so clear (see list 3). -<br/><br/> - -List 1 -- Examples of (presumably) normative Notes: -<br/> - -20.7.9.1 [allocator.members], p3,<br/> -20.7.9.1 [allocator.members], p10,<br/> -21.4.2 [string.cons], p11,<br/> -22.3.1.2 [locale.cons], p11,<br/> -23.3.3.4 [deque.modifiers], p2,<br/> -25.4.7 [alg.min.max], p3,<br/> -26.4.6 [complex.ops], p15,<br/> -27.6.3.4.3 [streambuf.virt.get], p7.<br/> -<br/> - -List 2 -- Examples of (presumably) informative Notes: -<br/> - -18.6.1.3 [new.delete.placement], p3,<br/> -21.4.6.6 [string::replace], p14,<br/> -22.4.1.4.2 [locale.codecvt.virtuals], p3,<br/> -25.2.4 [alg.foreach], p4,<br/> -26.4.5 [complex.member.ops], p1,<br/> -27.5.3.5 [ios.base.storage], p6.<br/> -<br/> - -List 3 -- Examples of Notes that are not clearly either normative -or informative: -<br/> - -22.3.1.2 [locale.cons], p8,<br/> -22.3.1.5 [locale.statics], p6,<br/> -27.6.3.4.5 [streambuf.virt.put], p4.<br/> -<br/> - -None of these lists is meant to be exhaustive. -</p> - -<p><i>[Definitely a real problem. The big problem is there's material - that doesn't quite fit any of the named paragraph categories - (e.g. <b>Effects</b>). Either we need a new kind of named - paragraph, or we need to put more material in unnamed paragraphs - jsut after the signature. We need to talk to the Project Editor - about how to do this. -]</i></p> - - -<p><i>[ -Bellevue: Specifics of list 3: First 2 items correct in std (22.1.1.2, -22.1.1.5) Third item should be non-normative (27.5.2.4.5), which Pete -will handle editorially. -]</i></p> - - -<p><i>[ -post San Francisco: Howard: reopened, needs attention. -]</i></p> - - -<p><i>[Pete: I changed the paragraphs marked "Note" and "Notes" to use "Remark" and "Remarks". -Fixed as editorial. This change has been in the WD since the post-Redmond mailing, in 2004. -Recommend NAD.]</i></p> - - -<p><i>[ -Batavia: We feel that the references in List 2 above should be changed from <i>Remarks</i> -to <i>Notes</i>. We also feel that those items in List 3 need to be double checked for -the same change. Alan and Pete to review. -]</i></p> - - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -A spot-check of List 2 suggests the issue is still relevant, -and a review of List 3 still seems called-for. -</p> -<p> -Move to NAD Editorial. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - -<hr> -<h3><a name="429"></a>429. typo in basic_ios::clear(iostate)</h3> -<p><b>Section:</b> 27.5.5.4 [iostate.flags] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2003-09-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iostate.flags">issues</a> in [iostate.flags].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#412">412</a></p> -<p><b>Discussion:</b></p> - <p> - -The Effects clause in 27.4.4.3, p5 describing the effects of a call to -the ios_base member function clear(iostate state) says that the function -only throws if the respective bits are already set prior to the function -call. That's obviously not the intent. If it was, a call to clear(badbit) -on an object for which (rdstate() == goodbit && exceptions() == badbit) -holds would not result in an exception being thrown. - - </p> - - <p><b>Proposed resolution:</b></p> - <p> - -The text ought to be changed from -<br/> - -"If (rdstate() & exceptions()) == 0, returns. ..." -<br/> - -to -<br/> - -"If (state & exceptions()) == 0, returns. ..." - </p> - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="433"></a>433. Contradiction in specification of unexpected()</h3> -<p><b>Section:</b> D.8.4 [unexpected] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Vyatcheslav Sysoltsev <b>Opened:</b> 2003-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Clause 15.5.2 [except.unexpected] paragraph 1 says that "void unexpected(); -is called (18.7.2) immediately after completing the stack unwinding -for the former function", but 18.7.2.4 (Effects) says that "void -unexpected(); . . . Calls the unexpected_handler function in effect -immediately after evaluating the throwexpression (18.7.2.2),". Isn't -here a contradiction: 15.5.2 requires stack have been unwound when in -void unexpected() and therefore in unexpected_handler but 18.7.2.4 -claims that unexpected_handler is called "in effect immediately" after -evaluation of throw expression is finished, so there is no space left -for stack to be unwound therefore? I think the phrase "in effect -immediately" should be removed from the standard because it brings -ambiguity in understanding. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>There is no contradiction. The phrase "in effect immediately" is - just to clarify which handler is to be called.</p> - - - - - -<hr> -<h3><a name="437"></a>437. Formatted output of function pointers is confusing</h3> -<p><b>Section:</b> 27.7.3.6.2 [ostream.inserters.arithmetic] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Ivan Godard <b>Opened:</b> 2003-10-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ostream.inserters.arithmetic">issues</a> in [ostream.inserters.arithmetic].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Given: -</p> -<pre> -void f(int) {} -void(*g)(int) = f; -cout << g; -</pre> - -<p> -(with the expected #include and usings), the value printed is a rather -surprising "true". Rather useless too. -</p> - -<p>The standard defines:</p> - -<pre>ostream& operator<<(ostream&, void*);</pre> - -<p>which picks up all data pointers and prints their hex value, but does -not pick up function pointers because there is no default conversion -from function pointer to void*. Absent that, we fall back to legacy -conversions from C and the function pointer is converted to bool. -</p> - -<p>There should be an analogous inserter that prints the address of a - function pointer.</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>This is indeed a wart, but there is no good way to solve it. C - doesn't provide a portable way of outputting the address of a - function point either.</p> - - - - - -<hr> -<h3><a name="439"></a>439. Should facets be copyable?</h3> -<p><b>Section:</b> 22.4 [locale.categories] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2003-11-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.categories">issues</a> in [locale.categories].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The following facets classes have no copy constructors described in - the standard, which, according to the standard, means that they are - supposed to use the compiler-generated defaults. Default copy - behavior is probably inappropriate. We should either make these - classes uncopyable or else specify exactly what their constructors do.</p> - -<p>Related issue: <a href="lwg-closed.html#421">421</a>.</p> - -<pre> - ctype_base - ctype - ctype_byname - ctype<char> - ctype_byname<char> - codecvt_base - codecvt - codecvt_byname - num_get - num_put - numpunct - numpunct_byname - collate - collate_byname - time_base - time_get - time_get_byname - time_put - time_put_byname - money_get - money_put - money_base - moneypunct - moneypunct_byname - messages_base - messages - messages_byname -</pre> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>The copy constructor in the base class is private.</p> - - - - - -<hr> -<h3><a name="440"></a>440. Should std::complex use unqualified transcendentals?</h3> -<p><b>Section:</b> 26.4.8 [complex.transcendentals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2003-11-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Operations like <tt>pow</tt> and <tt>exp</tt> on -<tt>complex<T></tt> are typically implemented in terms of -operations like <tt>sin</tt> and <tt>cos</tt> on <tt>T</tt>. -Should implementations write this as <tt>std::sin</tt>, or as plain -unqualified <tt>sin</tt>? -</p> - -<p>The issue, of course, is whether we want to use -argument-dependent lookup in the case where <tt>T</tt> is a -user-defined type. This is similar to the issue of valarray -transcendentals, as discussed in issue <a href="lwg-defects.html#226">226</a>.</p> - -<p>This issue differs from valarray transcendentals in two important -ways. First, "the effect of instantiating the template -<tt>complex</tt> for types other than float, double or long double is -unspecified." (26.4.1 [complex.syn]) Second, the standard does not -dictate implementation, so there is no guarantee that a particular -real math function is used in the implementation of a particular -complex function.</p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>If you instantiate std::complex for user-defined types, all bets -are off.</p> - - - - - -<hr> -<h3><a name="446"></a>446. Iterator equality between different containers</h3> -<p><b>Section:</b> 24.2 [iterator.requirements], 23.2 [container.requirements] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Andy Koenig <b>Opened:</b> 2003-12-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iterator.requirements">issues</a> in [iterator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -What requirements does the standard place on equality comparisons between -iterators that refer to elements of different containers. For example, if -<tt>v1</tt> and <tt>v2</tt> are empty vectors, is <tt>v1.end() == v2.end()</tt> -allowed to yield true? Is it allowed to throw an exception? -</p> - -<p> -The standard appears to be silent on both questions. -</p> -<p><i>[Sydney: The intention is that comparing two iterators from -different containers is undefined, but it's not clear if we say that, -or even whether it's something we should be saying in clause 23 or in -clause 24. Intuitively we might want to say that equality is defined -only if one iterator is reachable from another, but figuring out how -to say it in any sensible way is a bit tricky: reachability is defined -in terms of equality, so we can't also define equality in terms of -reachability. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Daniel volunteered to work on this. -</p></blockquote> - -<p><i>[ -2009-09-20 Daniel provided wording. -]</i></p> - - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Leave as Open. Alisdair has volunteered to refine the wording. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: Moved to NAD Editorial. Rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -Solved by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3066.html">N3066</a>. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Insert a new paragraph between 24.2 [iterator.requirements]/7+8: -</p> - -<blockquote> -<p> -[..] The result of the application of functions in the library to invalid -ranges is undefined. -</p> - -<p><ins>The result of directly or indirectly evaluating any comparison function -or the binary - operator with two iterator values as arguments that -were obtained -from two different ranges <tt>r1</tt> and <tt>r2</tt> (including their past-the-end values) which -are not subranges of one common range is undefined, unless explicitly -described otherwise.</ins> -</p> - -</blockquote> - - - - - - -<hr> -<h3><a name="447"></a>447. Wrong template argument for time facets</h3> -<p><b>Section:</b> 22.3.1.1.1 [locale.category] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2003-12-26 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.category">issues</a> in [locale.category].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#327">327</a></p> -<p><b>Discussion:</b></p> -<p> -22.1.1.1.1/4, table 52, "Required Instantiations", lists, among others: -</p> -<pre> - time_get<char,InputIterator> - time_get_byname<char,InputIterator> - time_get<wchar_t,OutputIterator> - time_get_byname<wchar_t,OutputIterator> -</pre> - -<p> -The second argument to the last two should be InputIterator, not -OutputIterator. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change the second template argument to InputIterator. -</p> - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="450"></a>450. set::find is inconsistent with associative container requirements</h3> -<p><b>Section:</b> 23.4.6 [set] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Bill Plauger <b>Opened:</b> 2004-01-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#set">issues</a> in [set].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#214">214</a></p> -<p><b>Discussion:</b></p> -<p>map/multimap have:</p> - -<pre> - iterator find(const key_type& x) const; - const_iterator find(const key_type& x) const; -</pre> - -<p> -which is consistent with the table of associative container requirements. -But set/multiset have: -</p> -<pre> - iterator find(const key_type&) const; -</pre> - -<p> -set/multiset should look like map/multimap, and honor the requirements -table, in this regard. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="451"></a>451. Associative erase should return an iterator</h3> -<p><b>Section:</b> 23.2.4 [associative.reqmts], 23.4 [associative] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Bill Plauger <b>Opened:</b> 2004-01-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#130">130</a></p> -<p><b>Discussion:</b></p> -<p>map/multimap/set/multiset have:</p> -<pre> - void erase(iterator); - void erase(iterator, iterator); -</pre> - -<p>But there's no good reason why these can't return an iterator, as for -vector/deque/list:</p> -<pre> - iterator erase(iterator); - iterator erase(iterator, iterator); -</pre> - - - -<p><b>Proposed resolution:</b></p> -<p> -Informally: The table of associative container requirements, and the -relevant template classes, should return an iterator designating the -first element beyond the erased subrange. -</p> - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="452"></a>452. locale::combine should be permitted to generate a named locale</h3> -<p><b>Section:</b> 22.3.1.3 [locale.members] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Bill Plauger <b>Opened:</b> 2004-01-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.members">issues</a> in [locale.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<pre> -template<class Facet> - locale::combine(const locale&) const; -</pre> -<p> -is obliged to create a locale that has no name. This is overspecification -and overkill. The resulting locale should follow the usual rules -- it -has a name if the locale argument has a name and Facet is one of the -standard facets. -</p> - -<p><i>[ - Sydney and post-Sydney (see c++std-lib-13439, c++std-lib-13440, - c++std-lib-13443): agreed that it's overkill to say that the locale - is obligated to be nameless. However, we also can't require it to - have a name. At the moment, locale names are based on categories - and not on individual facets. If a locale contains two different - facets of different names from the same category, then this would - not fit into existing naming schemes. We need to give - implementations more freedom. Bill will provide wording. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p>After further discussion the LWG decided to close this as NAD. - The fundamental problem is that names right now are per-category, - not per-facet. The <tt>combine</tt> member function works at the - wrong level of granularity.</p> - - - - - -<hr> -<h3><a name="454"></a>454. <tt>basic_filebuf::open</tt> should accept <tt>wchar_t</tt> names</h3> -<p><b>Section:</b> 27.9.1.4 [filebuf.members] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Bill Plauger <b>Opened:</b> 2004-01-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#filebuf.members">issues</a> in [filebuf.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-closed.html#105">105</a></p> -<p><b>Discussion:</b></p> -<pre> - basic_filebuf *basic_filebuf::open(const char *, ios_base::open_mode); -</pre> - -<p>should be supplemented with the overload:</p> - -<pre> - basic_filebuf *basic_filebuf::open(const wchar_t *, ios_base::open_mode); -</pre> - -<p> -Depending on the operating system, one of these forms is fundamental and -the other requires an implementation-defined mapping to determine the -actual filename. -</p> - -<p><i>[Sydney: Yes, we want to allow <tt>wchar_t</tt> filenames. Bill will - provide wording.]</i></p> - - -<p><i>[ -In Toronto we noted that this is issue 5 from -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1569.htm">N1569</a>. -]</i></p> - -<p> -How does this interact with the newly-defined character types, and how -do we avoid interface explosion considering <tt>std::string</tt> overloads that -were added? Propose another solution that is different than the -suggestion proposed by PJP. -</p> -<p> -Suggestion is to make a member template function for <tt>basic_string</tt> (for -<tt>char</tt>, <tt>wchar_t</tt>, <tt>u16char</tt>, <tt>u32char</tt> instantiations), and then just keep a -<tt>const char*</tt> member. -</p> -<p> -Goal is to do implicit conversion between character string literals to -appropriate <tt>basic_string</tt> type. Not quite sure if this is possible. -</p> -<p> -Implementors are free to add specific overloads for non-char character -types. -</p> - -<p><i>[ -Martin adds pre-Sophia Antipolis: -]</i></p> - - -<blockquote><p> -Please see <a href="http://wiki.dinkumware.com/twiki/pub/Wg21sophiaAntipolis/LibraryWorkingGroup/issue-454.html">issue 454: problems and solutions</a>. -</p></blockquote> - -<p><i>[ -Sophia Antipolis: -]</i></p> - - -<blockquote> -<p> -Beman is concerned that making these changes to <tt>basic_filebuf</tt> is not -usefully changed unless <tt>fstream</tt> is also changed; this also only handles -<tt>wchar_t</tt> and not other character types. -</p> -<p> -The TR2 filesystem library is a more complete solution, but is not available soon. -</p> -</blockquote> - -<p><i>[ -Martin adds: please reference -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2683.html">N2683</a> for -problems and solutions. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> - -<p>Change from:</p> -<blockquote> -<pre> -basic_filebuf<charT,traits>* open( - const char* s, - ios_base::openmode mode ); -</pre> - -<p> -Effects: If is_open() != false, returns a null pointer. -Otherwise, initializes the filebuf as required. It then -opens a file, if possible, whose name is the NTBS s ("as if" -by calling std::fopen(s,modstr)).</p> -</blockquote> - -<p>to:</p> - -<blockquote> -<pre> -basic_filebuf<charT,traits>* open( - const char* s, - ios_base::openmode mode ); - -basic_filebuf<charT,traits>* open( - const wchar_t* ws, - ios_base::openmode mode ); -</pre> - -<p> -<i>Effects</i>: If <tt>is_open() != false</tt>, returns a null pointer. -Otherwise, initializes the <tt>filebuf</tt> as required. It then -opens a file, if possible, whose name is the NTBS <tt>s</tt> ("as if" -by calling <tt>std::fopen(s,modstr)</tt>). -For the second signature, the NTBS <tt>s</tt> is determined from the -WCBS <tt>ws</tt> in an implementation-defined manner. -</p> - -<p> -(NOTE: For a system that "naturally" represents a filename -as a WCBS, the NTBS s in the first signature may instead -be mapped to a WCBS; if so, it follows the same mapping -rules as the first argument to open.) -</p> -</blockquote> - - - -<p><b>Rationale:</b></p> -<p> -Slightly controversial, but by a 7-1 straw poll the LWG agreed to move -this to Ready. The controversy was because the mapping between wide -names and files in a filesystem is implementation defined. The -counterargument, which most but not all LWG members accepted, is that -the mapping between narrow files names and files is also -implemenation defined.</p> - -<p><i>[Lillehammer: Moved back to "open" status, at Beman's urging. -(1) Why just basic_filebuf, instead of also basic_fstream (and -possibly other things too). (2) Why not also constructors that take -std::basic_string? (3) We might want to wait until we see Beman's -filesystem library; we might decide that it obviates this.]</i></p> - - -<p><i>[ -post Bellevue: -]</i></p> - - -<blockquote> -<p> -Move again to Ready. -</p> -<p> -There is a timing issue here. Since the filesystem library will not be -in C++0x, this should be brought forward. This solution would remain -valid in the context of the proposed filesystem. -</p> -<p> -This issue has been kicking around for a while, and the wchar_t addition -alone would help many users. Thus, we suggest putting this on the -reflector list with an invitation for someone to produce proposed -wording that covers basic_fstream. In the meantime, we suggest that the -proposed wording be adopted as-is. -</p> -<p> -If more of the Lillehammer questions come back, they should be -introduced as separate issues. -</p> -</blockquote> - -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote><p> -Some existing implementations provide overload already. Expected -filesystem "path" object overloads neatly, without surprises; implying -NAD. -</p></blockquote> - - - - - - - -<hr> -<h3><a name="458"></a>458. 24.1.5 contains unintended limitation for <tt>operator-</tt></h3> -<p><b>Section:</b> 24.2.7 [random.access.iterators] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Frey <b>Opened:</b> 2004-02-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#random.access.iterators">issues</a> in [random.access.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In 24.1.5 [lib.random.access.iterators], table 76 the operational -semantics for the expression "<tt>r -= n</tt>" are defined as "<tt>return r += -n</tt>". -This means, that the expression <tt>-n</tt> must be valid, which is not the case -for unsigned types. -</p> - -<p><i>[ -Sydney: Possibly not a real problem, since difference type is required -to be a signed integer type. However, the wording in the standard may -be less clear than we would like. -]</i></p> - - -<p><i>[ -Post Summit Alisdair adds: -]</i></p> - - -<blockquote> -<p> -This issue refers to a requirements table we have removed. -</p> -<p> -The issue might now relate to 24.2.7 [random.access.iterators] p5. -However, the rationale in the issue already recognises that the -<tt>difference_type</tt> must be signed, so this really looks NAD. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree with Alisdair's observations. -</p> -<p> -Move to NAD. -</p> -</blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote> -<p> -Need to look at again without concepts. -</p> -<p> -There was a question about this phrase in the discussion: "the -expression <tt>-n</tt> must be valid, which is not the case for unsigned types." -If <tt>n</tt> is an object of the iterator <tt>difference_type</tt> (eg <tt>ptrdiff_t</tt>), -then it is never unsigned. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -The group reviewed the wording in the draft and agreed that <tt>n</tt> is of -difference type, the difference type is signed, and the current wording -is correct. Moved to NAD. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -To remove this limitation, I suggest to change the -operational semantics for this column to: -</p> -<blockquote><pre> - { Distance m = n; - if (m >= 0) - while (m--) --r; - else - while (m++) ++r; - return r; } -</pre></blockquote> - - - - - - -<hr> -<h3><a name="459"></a>459. Requirement for widening in stage 2 is overspecification</h3> -<p><b>Section:</b> 22.4.2.1.2 [facet.num.get.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2004-03-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#facet.num.get.virtuals">active issues</a> in [facet.num.get.virtuals].</p> -<p><b>View all other</b> <a href="lwg-index.html#facet.num.get.virtuals">issues</a> in [facet.num.get.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>When parsing strings of wide-character digits, the standard - requires the library to widen narrow-character "atoms" and compare - the widened atoms against the characters that are being parsed. - Simply narrowing the wide characters would be far simpler, and - probably more efficient. The two choices are equivalent except in - convoluted test cases, and many implementations already ignore the - standard and use narrow instead of widen.</p> - -<p> -First, I disagree that using narrow() instead of widen() would -necessarily have unfortunate performance implications. A possible -implementation of narrow() that allows num_get to be implemented -in a much simpler and arguably comparably efficient way as calling -widen() allows, i.e. without making a virtual call to do_narrow every -time, is as follows: -</p> - -<pre> - inline char ctype<wchar_t>::narrow (wchar_t wc, char dflt) const - { - const unsigned wi = unsigned (wc); - - if (wi > UCHAR_MAX) - return typeid (*this) == typeid (ctype<wchar_t>) ? - dflt : do_narrow (wc, dflt); - - if (narrow_ [wi] < 0) { - const char nc = do_narrow (wc, dflt); - if (nc == dflt) - return dflt; - narrow_ [wi] = nc; - } - - return char (narrow_ [wi]); - } -</pre> - -<p> -Second, I don't think the change proposed in the issue (i.e., to use -narrow() instead of widen() during Stage 2) would be at all -drastic. Existing implementations with the exception of libstdc++ -currently already use narrow() so the impact of the change on programs -would presumably be isolated to just a single implementation. Further, -since narrow() is not required to translate alternate wide digit -representations such as those mentioned in issue <a href="lwg-defects.html#303">303</a> to -their narrow equivalents (i.e., the portable source characters '0' -through '9'), the change does not necessarily imply that these -alternate digits would be treated as ordinary digits and accepted as -part of numbers during parsing. In fact, the requirement in 22.4.1.1.2 [locale.ctype.virtuals], p13 forbids narrow() to translate an alternate -digit character, wc, to an ordinary digit in the basic source -character set unless the expression -(ctype<charT>::is(ctype_base::digit, wc) == true) holds. This in -turn is prohibited by the C standard (7.25.2.1.5, 7.25.2.1.5, and -5.2.1, respectively) for charT of either char or wchar_t. -</p> - -<p><i>[Sydney: To a large extent this is a nonproblem. As long as -you're only trafficking in char and wchar_t we're only dealing with a -stable character set, so you don't really need either 'widen' or -'narrow': can just use literals. Finally, it's not even clear whether -widen-vs-narrow is the right question; arguably we should be using -codecvt instead.]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -NAD. The standard is clear enough as written. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p>Change stage 2 so that implementations are permitted to use either -technique to perform the comparison:</p> -<ol> - <li> call widen on the atoms and compare (either by using - operator== or char_traits<charT>::eq) the input with - the widened atoms, or</li> - <li> call narrow on the input and compare the narrow input - with the atoms</li> - <li> do (1) or (2) only if charT is not char or wchar_t, - respectively; i.e., avoid calling widen or narrow - if it the source and destination types are the same</li> -</ol> - - - - - -<hr> -<h3><a name="462"></a>462. Destroying objects with static storage duration</h3> -<p><b>Section:</b> 3.6.3 [basic.start.term], 18.4 [cstdint] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Bill Plauger <b>Opened:</b> 2004-03-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -3.6.3 Termination spells out in detail the interleaving of static -destructor calls and calls to functions registered with atexit. To -match this behavior requires intimate cooperation between the code -that calls destructors and the exit/atexit machinery. The former -is tied tightly to the compiler; the latter is a primitive mechanism -inherited from C that traditionally has nothing to do with static -construction and destruction. The benefits of intermixing destructor -calls with atexit handler calls is questionable at best, and <i>very</i> -difficult to get right, particularly when mixing third-party C++ -libraries with different third-party C++ compilers and C libraries -supplied by still other parties. -</p> - -<p> -I believe the right thing to do is defer all static destruction -until after all atexit handlers are called. This is a change in -behavior, but one that is likely visible only to perverse test -suites. At the very least, we should <i>permit</i> deferred destruction -even if we don't require it. -</p> - -<p><i>[If this is to be changed, it should probably be changed by CWG. - At this point, however, the LWG is leaning toward NAD. Implementing - what the standard says is hard work, but it's not impossible and - most vendors went through that pain years ago. Changing this - behavior would be a user-visible change, and would break at least - one real application.]</i></p> - - -<p><i>[ -Batavia: Send to core with our recommendation that we should permit deferred -destruction but not require it. -]</i></p> - - -<p><i>[ -Howard: The course of action recommended in Batavia would undo LWG -issue <a href="lwg-defects.html#3">3</a> and break current code implementing the "phoenix -singleton". Search the net for "phoenix singleton atexit" to get a feel -for the size of the adverse impact this change would have. Below is -sample code which implements the phoenix singleton and would break if -<tt>atexit</tt> is changed in this way: -]</i></p> - - -<blockquote><pre> -#include <cstdlib> -#include <iostream> -#include <type_traits> -#include <new> - -class A -{ - bool alive_; - A(const A&); - A& operator=(const A&); -public: - A() : alive_(true) {std::cout << "A()\n";} - ~A() {alive_ = false; std::cout << "~A()\n";} - void use() - { - if (alive_) - std::cout << "A is alive\n"; - else - std::cout << "A is dead\n"; - } -}; - -void deallocate_resource(); - -// This is the phoenix singleton pattern -A& get_resource(bool create = true) -{ - static std::aligned_storage<sizeof(A), std::alignment_of<A>::value>::type buf; - static A* a; - if (create) - { - if (a != (A*)&buf) - { - a = ::new (&buf) A; - std::atexit(deallocate_resource); - } - } - else - { - a->~A(); - a = (A*)&buf + 1; - } - return *a; -} - -void deallocate_resource() -{ - get_resource(false); -} - -void use_A(const char* message) -{ - A& a = get_resource(); - std::cout << "Using A " << message << "\n"; - a.use(); -} - -struct B -{ - ~B() {use_A("from ~B()");} -}; - -B b; - -int main() -{ - use_A("from main()"); -} -</pre></blockquote> - -<p> -The correct output is: -</p> - -<blockquote><pre> -A() -Using A from main() -A is alive -~A() -A() -Using A from ~B() -A is alive -~A() -</pre></blockquote> - -<p><i>[ -Bellevue: Confirmed no interaction with <tt>quick_exit</tt>. -Strong feeling against mandating the change. Leaning towards NAD rather than permitting the change, -as this would make common implementations of pheonix-singleton pattern implementation defined, as noted by Howard. -Bill agrees issue is no longer serious, and accepts NAD. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="463"></a>463. <tt>auto_ptr</tt> usability issues</h3> -<p><b>Section:</b> X [auto.ptr] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Rani Sharoni <b>Opened:</b> 2003-12-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#auto.ptr">issues</a> in [auto.ptr].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -TC1 CWG DR #84 effectively made the <tt>template<class Y> operator auto_ptr<Y>()</tt> -member of <tt>auto_ptr</tt> (20.4.5.3/4) obsolete. -</p> - -<p> -The sole purpose of this obsolete conversion member is to enable copy -initialization base from r-value derived (or any convertible types like -cv-types) case: -</p> -<pre> -#include <memory> -using std::auto_ptr; - -struct B {}; -struct D : B {}; - -auto_ptr<D> source(); -int sink(auto_ptr<B>); -int x1 = sink( source() ); // #1 EDG - no suitable copy constructor -</pre> - -<p> -The excellent analysis of conversion operations that was given in the final -<tt>auto_ptr</tt> proposal -(http://www.open-std.org/jtc1/sc22/wg21/docs/papers/1997/N1128.pdf) -explicitly specifies this case analysis (case 4). DR #84 makes the analysis -wrong and actually comes to forbid the loophole that was exploited by the -<tt>auto_ptr</tt> designers. -</p> - -<p> -I didn't encounter any compliant compiler (e.g. EDG, GCC, BCC and VC) that -ever allowed this case. This is probably because it requires 3 user defined -conversions and in fact current compilers conform to DR #84. -</p> - -<p> -I was surprised to discover that the obsolete conversion member actually has -negative impact of the copy initialization base from l-value derived -case:</p> -<pre> -auto_ptr<D> dp; -int x2 = sink(dp); // #2 EDG - more than one user-defined conversion applies -</pre> - -<p> -I'm sure that the original intention was allowing this initialization using -the <tt>template<class Y> auto_ptr(auto_ptr<Y>& a)</tt> constructor (20.4.5.1/4) but -since in this copy initialization it's merely user defined conversion (UDC) -and the obsolete conversion member is UDC with the same rank (for the early -overloading stage) there is an ambiguity between them. -</p> - -<p> -Removing the obsolete member will have impact on code that explicitly -invokes it: -</p> -<pre> -int y = sink(source().operator auto_ptr<B>()); -</pre> - -<p> -IMHO no one ever wrote such awkward code and the reasonable workaround for -#1 is: -</p> -<pre> -int y = sink( auto_ptr<B>(source()) ); -</pre> - -<p> -I was even more surprised to find out that after removing the obsolete -conversion member the initialization was still ill-formed: -<tt>int x3 = sink(dp); // #3 EDG - no suitable copy constructor</tt> -</p> - -<p> -This copy initialization semantically requires copy constructor which means -that both template conversion constructor and the <tt>auto_ptr_ref</tt> conversion -member (20.4.5.3/3) are required which is what was explicitly forbidden in -DR #84. This is a bit amusing case in which removing ambiguity results with -no candidates. -</p> - -<p> -I also found exception safety issue with <tt>auto_ptr</tt> related to <tt>auto_ptr_ref</tt>: -</p> -<pre> -int f(auto_ptr<B>, std::string); -auto_ptr<B> source2(); - -// string constructor throws while auto_ptr_ref -// "holds" the pointer -int x4 = f(source2(), "xyz"); // #4 -</pre> - -<p> -The theoretic execution sequence that will cause a leak: -</p> -<ol> -<li>call auto_ptr<B>::operator auto_ptr_ref<B>()</li> -<li>call string::string(char const*) and throw</li> -</ol> - -<p> -According to 20.4.5.3/3 and 20.4.5/2 the <tt>auto_ptr_ref</tt> conversion member -returns <tt>auto_ptr_ref<Y></tt> that holds <tt>*this</tt> and this is another defect since -the type of <tt>*this</tt> is <tt>auto_ptr<X></tt> where <tt>X</tt> might -be different from <tt>Y</tt>. Several library vendors (e.g. SGI) implement -<tt>auto_ptr_ref<Y></tt> with <tt>Y*</tt> as member which -is much more reasonable. Other vendor implemented <tt>auto_ptr_ref</tt> as -defectively required and it results with awkward and catastrophic code: -<tt>int oops = sink(auto_ptr<B>(source())); // warning recursive on all control paths</tt> -</p> - -<p> -Dave Abrahams noticed that there is no specification saying that -<tt>auto_ptr_ref</tt> copy constructor can't throw. -</p> - -<p> -My proposal comes to solve all the above issues and significantly simplify -<tt>auto_ptr</tt> implementation. One of the fundamental requirements from -<tt>auto_ptr</tt> is that it can be constructed in an intuitive manner (i.e. -like ordinary pointers) but with strict ownership semantics which yield that source -<tt>auto_ptr</tt> in initialization must be non-const. My idea is to add additional -constructor template with sole propose to generate ill-formed, diagnostic -required, instance for const auto_ptr arguments during instantiation of -declaration. This special constructor will not be instantiated for other -types which is achievable using 14.8.2/2 (SFINAE). Having this constructor -in hand makes the constructor <tt>template<class Y> auto_ptr(auto_ptr<Y> const&)</tt> -legitimate since the actual argument can't be const yet non const r-value -are acceptable. -</p> - -<p> -This implementation technique makes the "private auxiliary class" -<tt>auto_ptr_ref</tt> obsolete and I found out that modern C++ compilers (e.g. EDG, -GCC and VC) consume the new implementation as expected and allow all -intuitive initialization and assignment cases while rejecting illegal cases -that involve const <tt>auto_ptr</tt> arguments. -</p> - -<p>The proposed auto_ptr interface:</p> - -<pre> -namespace std { - template<class X> class auto_ptr { - public: - typedef X element_type; - - // 20.4.5.1 construct/copy/destroy: - explicit auto_ptr(X* p=0) throw(); - auto_ptr(auto_ptr&) throw(); - template<class Y> auto_ptr(auto_ptr<Y> const&) throw(); - auto_ptr& operator=(auto_ptr&) throw(); - template<class Y> auto_ptr& operator=(auto_ptr<Y>) throw(); - ~auto_ptr() throw(); - - // 20.4.5.2 members: - X& operator*() const throw(); - X* operator->() const throw(); - X* get() const throw(); - X* release() throw(); - void reset(X* p=0) throw(); - - private: - template<class U> - auto_ptr(U& rhs, typename -unspecified_error_on_const_auto_ptr<U>::type = 0); - }; -} -</pre> - -<p> -One compliant technique to implement the <tt>unspecified_error_on_const_auto_ptr</tt> -helper class is using additional private <tt>auto_ptr</tt> member class template like -the following: -</p> -<pre> -template<typename T> struct unspecified_error_on_const_auto_ptr; - -template<typename T> -struct unspecified_error_on_const_auto_ptr<auto_ptr<T> const> -{ typedef typename auto_ptr<T>::const_auto_ptr_is_not_allowed type; }; -</pre> - -<p> -There are other techniques to implement this helper class that might work -better for different compliers (i.e. better diagnostics) and therefore I -suggest defining its semantic behavior without mandating any specific -implementation. IMO, and I didn't found any compiler that thinks otherwise, -14.7.1/5 doesn't theoretically defeat the suggested technique but I suggest -verifying this with core language experts. -</p> - -<p><b>Further changes in standard text:</b></p> -<p>Remove section 20.4.5.3</p> - -<p>Change 20.4.5/2 to read something like: -Initializing <tt>auto_ptr<X></tt> from <tt>const auto_ptr<Y></tt> will result with unspecified -ill-formed declaration that will require unspecified diagnostic.</p> - -<p>Change 20.4.5.1/4,5,6 to read:</p> - -<pre>template<class Y> auto_ptr(auto_ptr<Y> const& a) throw();</pre> -<p> 4 <i>Requires</i>: <tt>Y*</tt> can be implicitly converted to <tt>X*</tt>.</p> -<p> 5 <i>Effects</i>: Calls <tt>const_cast<auto_ptr<Y>&>(a).release()</tt>.</p> -<p> 6 <i>Postconditions</i>: <tt>*this</tt> holds the pointer returned from <tt>a.release()</tt>.</p> - -<p>Change 20.4.5.1/10</p> -<pre> -template<class Y> auto_ptr& operator=(auto_ptr<Y> a) throw(); -</pre> -<p> -10 <i>Requires</i>: <tt>Y*</tt> can be implicitly converted to <tt>X*</tt>. The expression <tt>delete -get()</tt> is well formed. -</p> - -<p>LWG TC DR #127 is obsolete.</p> - -<p> -Notice that the copy constructor and copy assignment operator should remain -as before and accept non-<tt>const auto_ptr&</tt> since they have effect on the form -of the implicitly declared copy constructor and copy assignment operator of -class that contains auto_ptr as member per 12.8/5,10: -</p> -<pre> -struct X { - // implicit X(X&) - // implicit X& operator=(X&) - auto_ptr<D> aptr_; -}; -</pre> - -<p> -In most cases this indicates about sloppy programming but preserves the -current <tt>auto_ptr</tt> behavior. -</p> - -<p> -Dave Abrahams encouraged me to suggest fallback implementation in case that -my suggestion that involves removing of <tt>auto_ptr_ref</tt> will not be accepted. -In this case removing the obsolete conversion member to <tt>auto_ptr<Y></tt> and -20.4.5.3/4,5 is still required in order to eliminate ambiguity in legal -cases. The two constructors that I suggested will co exist with the current -members but will make <tt>auto_ptr_ref</tt> obsolete in initialization contexts. -<tt>auto_ptr_ref</tt> will be effective in assignment contexts as suggested in DR -#127 and I can't see any serious exception safety issues in those cases -(although it's possible to synthesize such). <tt>auto_ptr_ref<X></tt> semantics will -have to be revised to say that it strictly holds pointer of type <tt>X</tt> and not -reference to an <tt>auto_ptr</tt> for the favor of cases in which <tt>auto_ptr_ref<Y></tt> is -constructed from <tt>auto_ptr<X></tt> in which <tt>X</tt> is different from -<tt>Y</tt> (i.e. assignment from r-value derived to base). -</p> - -<p><i>[Redmond: punt for the moment. We haven't decided yet whether we - want to fix auto_ptr for C++-0x, or remove it and replace it with - move_ptr and unique_ptr.]</i></p> - - -<p><i>[ -Oxford 2007: Recommend NAD. We're just going to deprecate it. It still works for simple use cases -and people know how to deal with it. Going forward <tt>unique_ptr</tt> is the recommended -tool. -]</i></p> - - -<p><i>[ -2007-11-09: Reopened at the request of David Abrahams, Alisdair Meredith and Gabriel Dos Reis. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -This is a complicated issue, so we agreed to defer discussion until -later in the week so that interested parties can read up on it. -</p></blockquote> - -<p><i>[ -2009-10-04 Daniel adds: -]</i></p> - - -<blockquote> -<p> -I suggest to close this issue as NAD. The reasons are two-fold: First, the -suggested proposed resolution uses no longer appropriate language means -to solve this issue, which has the effect that the recommended resolution is -another - but better - form of hack. Second, either following the suggested -resolution or the now more natural alternative via the added member set -</p> - -<blockquote><pre> -template<class Y> auto_ptr(auto_ptr<Y>&&) throw(); -template<class Y> auto_ptr& operator=(auto_ptr<Y>&&) throw(); -</pre></blockquote> - -<p> -would still have a non-zero probability to break user-code that actively -references <tt>auto_ptr_ref</tt>. This risk seems to indicate that a -decision which would not touch the current spec of <tt>auto_ptr</tt> at -all (but deprecating it) and instead recommending to use -<tt>unique_ptr</tt> for new code instead might have the best -cost-benefit ratio. IMO the current solution of <a href="lwg-defects.html#1100">1100</a> can -be considered as an active user-support for this transition. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD. Alisdair will open a new issue (<a href="lwg-defects.html#1247">1247</a>) with -proposed wording to handle <tt>auto_ptr_ref</tt>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change the synopsis in X [auto.ptr]: -</p> - -<blockquote><pre> -namespace std { - <del>template <class Y> struct auto_ptr_ref {};</del> - - <ins>// exposition only</ins> - <ins>template <class T> struct constant_object;</ins> - - <ins>// exposition only</ins> - <ins>template <class T></ins> - <ins>struct cannot_transfer_ownership_from</ins> - <ins>: constant_object<T> {};</ins> - - template <class X> class auto_ptr { - public: - typedef X element_type; - - // D.9.1.1 construct/copy/destroy: - explicit auto_ptr(X* p =0) throw(); - auto_ptr(auto_ptr&) throw(); - template<class Y> auto_ptr(auto_ptr<Y><ins> const</ins>&) throw(); - auto_ptr& operator=(auto_ptr&) throw(); - template<class Y> auto_ptr& operator=(auto_ptr<Y><del>&</del>) throw(); - <del>auto_ptr& operator=(auto_ptr_ref<X> r) throw();</del> - ~auto_ptr() throw(); - - // D.9.1.2 members: - X& operator*() const throw(); - X* operator->() const throw(); - X* get() const throw(); - X* release() throw(); - void reset(X* p =0) throw(); - - <del>// D.9.1.3 conversions:</del> - <del>auto_ptr(auto_ptr_ref<X>) throw();</del> - <del>template<class Y> operator auto_ptr_ref<Y>() throw();</del> - <del>template<class Y> operator auto_ptr<Y>() throw();</del> - - <ins>// exposition only</ins> - <ins>template<class U></ins> - <ins>auto_ptr(U& rhs, typename cannot_transfer_ownership_from<U>::error = 0);</ins> - }; - - template <> class auto_ptr<void> - { - public: - typedef void element_type; - }; - -} -</pre></blockquote> - -<p> -Remove X [auto.ptr.conv]. -</p> - -<p> -Change X [auto.ptr], p3: -</p> - -<blockquote><p> -The <tt>auto_ptr</tt> provides a semantics of strict ownership. An -<tt>auto_ptr</tt> owns the object it holds a pointer to. Copying an -<tt>auto_ptr</tt> copies the pointer and transfers ownership to the -destination. If more than one <tt>auto_ptr</tt> owns the same object at -the same time the behavior of the program is undefined. <ins>Templates -<tt>constant_object</tt> and <tt>cannot_transfer_ownership_from</tt>, -and the final constructor of <tt>auto_ptr</tt> are for exposition only. -For any types <tt>X</tt> and <tt>Y</tt>, initializing -<tt>auto_ptr<X></tt> from <tt>const auto_ptr<Y></tt> is -ill-formed, diagnostic required.</ins> [<i>Note:</i> The uses of -<tt>auto_ptr</tt> include providing temporary exception-safety for -dynamically allocated memory, passing ownership of dynamically allocated -memory to a function, and returning dynamically allocated memory from a -function. <tt>auto_ptr</tt> does not meet the <tt>CopyConstructible</tt> -and <tt>Assignable</tt> requirements for Standard Library container -elements and thus instantiating a Standard Library container with an -<tt>auto_ptr</tt> results in undefined behavior. <i>-- end note</i>] -</p></blockquote> - -<p> -Change [auto.ptr.cons], p5: -</p> - -<blockquote> -<pre> -template<class Y> auto_ptr(auto_ptr<Y><ins> const</ins>& a) throw(); -</pre> -<blockquote> -<p> -<i>Requires:</i> <tt>Y*</tt> can be implicitly converted to <tt>X*</tt>. -</p> -<p> -<i>Effects:</i> Calls <ins><tt>const_cast<auto_ptr<Y>&>(</tt></ins><tt>a</tt><ins><tt>)</tt></ins><tt>.release()</tt>. -</p> -<p> -<i>Postconditions:</i> <tt>*this</tt> holds the pointer returned from <tt>a.release()</tt>. -</p> -</blockquote> -</blockquote> - -<p> -Change [auto.ptr.cons], p10: -</p> - -<blockquote> -<pre> -template<class Y> auto_ptr& operator=(auto_ptr<Y><del>&</del> a) throw(); -</pre> -<blockquote> -<p> -<i>Requires:</i> <tt>Y*</tt> can be implicitly converted to <tt>X*</tt>. -The expression <tt>delete get()</tt> is well formed. -</p> -<p> -<i>Effects:</i> Calls <tt>reset(a.release())</tt>. -</p> -<p> -<i>Returns:</i> <tt>*this</tt>. -</p> -</blockquote> -</blockquote> - - - - - - -<hr> -<h3><a name="466"></a>466. <tt>basic_string</tt> ctor should prevent null pointer error</h3> -<p><b>Section:</b> 21.4.1 [string.require] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Frey <b>Opened:</b> 2004-06-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string.require">issues</a> in [string.require].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Today, my colleagues and me wasted a lot of time. After some time, I -found the problem. It could be reduced to the following short example: -</p> - -<pre> - #include <string> - int main() { std::string( 0 ); } -</pre> - -<p>The problem is that the tested compilers (GCC 2.95.2, GCC 3.3.1 and -Comeau online) compile the above without errors or warnings! The -programs (at least for the GCC) resulted in a SEGV.</p> - -<p>I know that the standard explicitly states that the ctor of string -requires a <tt>char*</tt> which is not zero. STLs could easily detect the above -case with a private ctor for <tt>basic_string</tt> which takes a single '<tt>int</tt>' -argument. This would catch the above code at compile time and would not -ambiguate any other legal ctors.</p> - -<p><i>[Redmond: No great enthusiasm for doing this. If we do, - however, we want to do it for all places that take <tt>charT*</tt> - pointers, not just the single-argument constructor. The other - question is whether we want to catch this at compile time (in which - case we catch the error of a literal 0, but not an expression whose - value is a null pointer), at run time, or both. - Recommend NAD. Relegate this functionality to debugging implementations.]</i></p> - - -<p><i>[ -Post Summit: Alisdair requests this be re-opened as several new language facilities are -designed to solve exactly this kind of problem. -]</i></p> - - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We are unable to achieve consensus on an approach to a resolution. -There is some sentiment for treating this as a QOI matter. -It is also possible -that when <tt>string</tt> is brought into the concepts world, -this issue might be addressed in that context. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -We considered three options: -</p> - -<ul> -<li>The proposed resolution.</li> -<li>NAD</li> -<li>Interpret a null pointer as the empty string.</li> -</ul> - -<p> -The consensus was NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add to the synopsis in 21.4 [basic.string] -</p> - -<blockquote><pre> -<ins>basic_string( nullptr_t ) = delete;</ins> -</pre></blockquote> - - - - - -<hr> -<h3><a name="470"></a>470. accessing containers from their elements' special functions</h3> -<p><b>Section:</b> 23 [containers] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2004-06-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#containers">active issues</a> in [containers].</p> -<p><b>View all other</b> <a href="lwg-index.html#containers">issues</a> in [containers].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -The standard doesn't prohibit the destructors (or any other special -functions) of containers' elements invoked from a member function -of the container from "recursively" calling the same (or any other) -member function on the same container object, potentially while the -container is in an intermediate state, or even changing the state -of the container object while it is being modified. This may result -in some surprising (i.e., undefined) behavior. -</p> - -<p>Read email thread starting with c++std-lib-13637 for more.</p> - - - -<p><b>Proposed resolution:</b></p> - -<p>Add to Container Requirements the following new paragraph:</p> - -<pre> - Unless otherwise specified, the behavior of a program that - invokes a container member function f from a member function - g of the container's value_type on a container object c that - called g from its mutating member function h, is undefined. - I.e., if v is an element of c, directly or indirectly calling - c.h() from v.g() called from c.f(), is undefined. -</pre> - -<p><i>[Redmond: This is a real issue, but it's probably a clause 17 - issue, not clause 23. We get the same issue, for example, if we - try to destroy a stream from one of the stream's callback functions.]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -Recommend NAD. We agree this is an issue, but not a defect. -We believe that there is no wording we can put in the standard -that will cover all cases without introducing unfortunate -corner cases. -</p> - - - - - -<hr> -<h3><a name="472"></a>472. Missing "Returns" clause in std::equal_range</h3> -<p><b>Section:</b> 25.4.3.3 [equal.range] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Prateek R Karandikar <b>Opened:</b> 2004-06-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#equal.range">issues</a> in [equal.range].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#270">270</a></p> -<p><b>Discussion:</b></p> -<p> -There is no "Returns:" clause for std::equal_range, which returns non-void. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>Fixed as part of issue <a href="lwg-defects.html#270">270</a>.</p> - - - - - - -<hr> -<h3><a name="476"></a>476. Forward Iterator implied mutability</h3> -<p><b>Section:</b> 24.2.5 [forward.iterators] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Dave Abrahams <b>Opened:</b> 2004-07-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#forward.iterators">issues</a> in [forward.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p>24.1/3 says:</p> -<blockquote><p> - Forward iterators satisfy all the requirements of the input and - output iterators and can be used whenever either kind is specified -</p></blockquote> - -<p> -The problem is that satisfying the requirements of output iterator -means that you can always assign *something* into the result of -dereferencing it. That makes almost all non-mutable forward -iterators non-conforming. I think we need to sever the refinement -relationship between forward iterator and output iterator. -</p> - -<p>Related issue: <a href="lwg-defects.html#200">200</a>. But this is not a dup.</p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>Yes, 24.1/3 does say that. But it's introductory material. The -precise specification is in 24.1.3, and the requrements table there is -right. We don't need to fine-tune introductory wording. (Especially -since this wording is likely to be changed as part of the iterator -overhaul.)</p> - - - - - -<hr> -<h3><a name="477"></a>477. Operator-> for const forward iterators</h3> -<p><b>Section:</b> 24.2.5 [forward.iterators] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Dave Abrahams <b>Opened:</b> 2004-07-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#forward.iterators">issues</a> in [forward.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#478">478</a></p> -<p><b>Discussion:</b></p> -<p> -The Forward Iterator requirements table contains the following: -</p> -<pre> - expression return type operational precondition - semantics - ========== ================== =========== ========================== - a->m U& if X is mutable, (*a).m pre: (*a).m is well-defined. - otherwise const U& - - r->m U& (*r).m pre: (*r).m is well-defined. -</pre> - -<p> -The first line is exactly right. The second line is wrong. Basically -it implies that the const-ness of the iterator affects the const-ness -of referenced members. But Paragraph 11 of [lib.iterator.requirements] says: -</p> - -<blockquote><p> - In the following sections, a and b denote values of type const X, n - denotes a value of the difference type Distance, u, tmp, and m - denote identifiers, r denotes a value of X&, t denotes a value of - value type T, o denotes a value of some type that is writable to - the output iterator. -</p></blockquote> - -<p>AFAICT if we need the second line at all, it should read the same -as the first line.</p> - -<p>Related issue: <a href="lwg-defects.html#478">478</a></p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>The LWG agrees that this is a real problem. Marked as a DUP - because the LWG chose to adopt the solution proposed in - <a href="lwg-defects.html#478">478</a>. -</p> - - - - - -<hr> -<h3><a name="479"></a>479. Container requirements and placement new</h3> -<p><b>Section:</b> 23.2 [container.requirements] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Herb Sutter <b>Opened:</b> 2004-08-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#container.requirements">active issues</a> in [container.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#container.requirements">issues</a> in [container.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-closed.html#580">580</a></p> -<p><b>Discussion:</b></p> -<p>Nothing in the standard appears to make this program ill-formed:</p> - -<pre> - struct C { - void* operator new( size_t s ) { return ::operator new( s ); } - // NOTE: this hides in-place and nothrow new - }; - - int main() { - vector<C> v; - v.push_back( C() ); - } -</pre> - -<p>Is that intentional? We should clarify whether or not we intended - to require containers to support types that define their own special - versions of <tt>operator new</tt>.</p> - -<p><i>[ -Lillehammer: A container will definitely never use this overridden -operator new, but whether it will fail to compile is unclear from the -standard. Are containers supposed to use qualified or unqualified -placement new? 20.4.1.1 is somewhat relevant, but the standard -doesn't make it completely clear whether containers have to use -Allocator::construct(). If containers don't use it, the details of how -containers use placement new are unspecified. That is the real bug, -but it needs to be fixed as part of the allocator overhaul. Weak -support that the eventual solution should make this code well formed. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> - - - - - - - -<hr> -<h3><a name="480"></a>480. unary_function and binary_function should have protected nonvirtual destructors</h3> -<p><b>Section:</b> X [depr.base] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Joe Gottman <b>Opened:</b> 2004-08-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#depr.base">issues</a> in [depr.base].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The classes std::unary_function and std::binary_function are both -designed to be inherited from but contain no virtual functions. This -makes it too easy for a novice programmer to write code like -binary_function<int, int, int> *p = new plus<int>; delete p;</p> - -<p>There are two common ways to prevent this source of undefined -behavior: give the base class a public virtual destructor, or give it -a protected nonvirtual destructor. Since unary_function and -binary_function have no other virtual functions, (note in particular -the absence of an operator()() ), it would cost too much to give them -public virtual destructors. Therefore, they should be given protected -nonvirtual destructors.</p> - - -<p><b>Proposed resolution:</b></p> -<p>Change Paragraph 20.3.1 of the Standard from</p> -<pre> - template <class Arg, class Result> - struct unary_function { - typedef Arg argument_type; - typedef Result result_type; - }; - - template <class Arg1, class Arg2, class Result> - struct binary_function { - typedef Arg1 first_argument_type; - typedef Arg2 second_argument_type; - typedef Result result_type; - }; -</pre> - -<p>to</p> -<pre> - template <class Arg, class Result> - struct unary_function { - typedef Arg argument_type; - typedef Result result_type; - protected: - ~unary_function() {} - }; - - template <class Arg1, class Arg2, class Result> - struct binary_function { - typedef Arg1 first_argument_type; - typedef Arg2 second_argument_type; - typedef Result result_type; - protected: - ~binary_function() {} - }; -</pre> - - -<p><b>Rationale:</b></p> -<p>The LWG doesn't believe the existing definition causes anybody any - concrete harm.</p> - - - - - -<hr> -<h3><a name="481"></a>481. unique's effects on the range [result, last)</h3> -<p><b>Section:</b> 25.3.9 [alg.unique] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Andrew Koenig <b>Opened:</b> 2004-08-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.unique">issues</a> in [alg.unique].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The standard says that unique(first, last) "eliminates all but the -first element from every consecutive group of equal elements" in -[first, last) and returns "the end of the resulting range". So a -postcondition is that [first, result) is the same as the old [first, -last) except that duplicates have been eliminated. -</p> - -<p>What postconditions are there on the range [result, last)? One - might argue that the standard says nothing about those values, so - they can be anything. One might also argue that the standard - doesn't permit those values to be changed, so they must not be. - Should the standard say something explicit one way or the other?</p> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p> -<p>We don't want to make many guarantees about what's in [result, -end). Maybe we aren't being quite explicit enough about not being -explicit, but it's hard to think that's a major problem.</p> - - - - - -<hr> -<h3><a name="483"></a>483. Heterogeneous equality and EqualityComparable</h3> -<p><b>Section:</b> 25.2 [alg.nonmodifying], 25.3 [alg.modifying.operations] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Peter Dimov <b>Opened:</b> 2004-09-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#283">283</a></p> -<p><b>Discussion:</b></p> -<p>c++std-lib-14262</p> - -<p>[lib.alg.find] requires T to be EqualityComparable:</p> - -<pre> -template <class InputIterator, class T> - InputIterator find(InputIterator first, InputIterator last, - const T& value); -</pre> - -<p> -However the condition being tested, as specified in the Effects -clause, is actually *i == value, where i is an InputIterator. -</p> - -<p> -The two clauses are in agreement only if the type of *i is T, but this -isn't necessarily the case. *i may have a heterogeneous comparison -operator that takes a T, or a T may be convertible to the type of *i. -</p> - -<p>Further discussion (c++std-lib-14264): this problem affects a - number of algorithsm in clause 25, not just <tt>find</tt>. We - should try to resolve this problem everywhere it appears.</p> - - -<p><b>Proposed resolution:</b></p> - -<p>[lib.alg.find]:</p> -<blockquote><p> - Remove [lib.alg.find]/1. -</p></blockquote> - -<p>[lib.alg.count]:</p> -<blockquote><p> - Remove [lib.alg.count]/1. -</p></blockquote> - -<p>[lib.alg.search]:</p> -<blockquote><p> - Remove "Type T is EqualityComparable (20.1.1), " from [lib.alg.search]/4. -</p></blockquote> - -<p>[lib.alg.replace]:</p> - -<blockquote> - <p> - Remove [lib.alg.replace]/1. - Replace [lb.alg.replace]/2 with: - </p> - - <blockquote><p> - For every iterator i in the range [first, last) for which *i == value - or pred(*i) holds perform *i = new_value. - </p></blockquote> - - <p> - Remove the first sentence of /4. - Replace the beginning of /5 with: - </p> - - <blockquote><p> - For every iterator i in the range [result, result + (last - - first)), assign to *i either... - </p></blockquote> - - <p>(Note the defect here, current text says assign to i, not *i).</p> -</blockquote> - -<p>[lib.alg.fill]:</p> - -<blockquote> - <p> - Remove "Type T is Assignable (23.1), " from /1. - Replace /2 with: - </p> - - <blockquote><p> - For every iterator i in the range [first, last) or [first, first + n), - perform *i = value. - </p></blockquote> -</blockquote> - -<p>[lib.alg.remove]:</p> -<blockquote><p> - Remove /1. - Remove the first sentence of /6. -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p>Duplicate of (a subset of) issue <a href="lwg-defects.html#283">283</a>.</p> - - - - - - -<hr> -<h3><a name="486"></a>486. min/max CopyConstructible requirement is too strict</h3> -<p><b>Section:</b> 25.4.7 [alg.min.max] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Dave Abrahams <b>Opened:</b> 2004-10-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.min.max">issues</a> in [alg.min.max].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#281">281</a></p> -<p><b>Discussion:</b></p> -<p>A straightforward implementation of these algorithms does not need to -copy T.</p> - - -<p><b>Proposed resolution:</b></p> -<p>drop the the words "and CopyConstructible" from paragraphs 1 and 4</p> - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="487"></a>487. Allocator::construct is too limiting</h3> -<p><b>Section:</b> 17.6.3.5 [allocator.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Dhruv Matani <b>Opened:</b> 2004-10-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#allocator.requirements">active issues</a> in [allocator.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#allocator.requirements">issues</a> in [allocator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The standard's version of allocator::construct(pointer, -const_reference) severely limits what you can construct using this -function. Say you can construct a socket from a file descriptor. Now, -using this syntax, I first have to manually construct a socket from -the fd, and then pass the constructed socket to the construct() -function so it will just to an uninitialized copy of the socket I -manually constructed. Now it may not always be possible to copy -construct a socket eh! So, I feel that the changes should go in the -allocator::construct(), making it: -</p> -<pre> - template<typename T> - struct allocator{ - template<typename T1> - void construct(pointer T1 const& rt1); - }; -</pre> - -<p> -Now, the ctor of the class T which matches the one that takes a T1 can -be called! Doesn't that sound great? -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>NAD. STL uses copying all the time, and making it possible for - allocators to construct noncopyable objects is useless in the - absence of corresponding container changes. We might consider this - as part of a larger redesign of STL.</p> - - - - - -<hr> -<h3><a name="489"></a>489. std::remove / std::remove_if wrongly specified</h3> -<p><b>Section:</b> 25.3.8 [alg.remove] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thomas Mang <b>Opened:</b> 2004-12-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.remove">issues</a> in [alg.remove].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>In Section 25.2.7 [lib.alg.remove], paragraphs 1 to 5 describe the -behavior of the mutating sequence operations std::remove and -std::remove_if. However, the wording does not reflect the intended -behavior [Note: See definition of intended behavior below] of these -algorithms, as it is known to the C++ community [1]. -</p> - - - -<p>1) Analysis of current wording:</p> - - -<p>25.2.7 [lib.alg.remove], paragraph 2:</p> - -<p>Current wording says: -"Effects: Eliminates all the elements referred to by iterator i in the -range [first, last) for which the following corresponding conditions -hold: *i == value, pred(*i) != false."</p> - -<p> -This sentences expresses specifically that all elements denoted by the -(original) range [first, last) for which the corresponding condition -hold will be eliminated. Since there is no formal definition of the term -"eliminate" provided, the meaning of "eliminate" in everyday language -implies that as postcondition, no element in the range denoted by -[first, last) will hold the corresponding condition on reiteration over -the range [first, last). -</p> - -<p> -However, this is neither the intent [Note: See definition of intended -behavior below] nor a general possible approach. It can be easily proven -that if all elements of the original range[first, last) will hold the -condition, it is not possible to substitute them by an element for which -the condition will not hold. -</p> - - -<p>25.2.7 [lib.alg.remove], paragraph 3:</p> - -<p> -Current wording says: -"Returns: The end of the resulting range." -</p> - -<p> -The resulting range is not specified. In combination with 25.2.7 -[lib.alg.remove], paragraph 2, the only reasonable interpretation of -this so-called resulting range is the range [first,last) - thus -returning always the ForwardIterator 'last' parameter. -</p> - - -<p> -25.2.7 [lib.alg.remove], paragraph 4: -</p> - -<p> -Current wording says: -"Notes: Stable: the relative order of the elements that are not removed -is the same as their relative order in the original range" -</p> - -<p> -This sentences makes use of the term "removed", which is neither -specified, nor used in a previous paragraph (which uses the term -"eliminate"), nor unamgiuously separated from the name of the algorithm. -</p> - - -<p>2) Description of intended behavior:</p> - -<p> -For the rest of this Defect Report, it is assumed that the intended -behavior was that all elements of the range [first, last) which do not -hold the condition *i == value (std::remove) or pred(*i) != false -(std::remove_if)], call them s-elements [Note: s...stay], will be placed -into a contiguous subrange of [first, last), denoted by the iterators -[first, return value). The number of elements in the resulting range -[first, return value) shall be equal to the number of s-elements in the -original range [first, last). The relative order of the elements in the -resulting subrange[first, return value) shall be the same as the -relative order of the corresponding elements in the original range. It -is undefined whether any elements in the resulting subrange [return -value, last) will hold the corresponding condition, or not. -</p> - -<p> -All implementations known to the author of this Defect Report comply -with this intent. Since the intent of the behavior (contrary to the -current wording) is also described in various utility references serving -the C++ community [1], it is not expected that fixing the paragraphs -will influence current code - unless the code relies on the behavior as -it is described by current wording and the implementation indeed -reflects the current wording, and not the intent. -</p> - - - -<p>3) Proposed fixes:</p> - - -<p>Change 25.2.7 [lib.alg.remove], paragraph 2 to:</p> - -<p> -"Effect: Places all the elements referred to by iterator i in the range -[first, last) for which the following corresponding conditions hold : -!(*i == value), pred(*i) == false into the subrange [first, k) of the -original range, where k shall denote a value of type ForwardIterator. It -is undefined whether any elements in the resulting subrange [k, last) -will hold the corresponding condition, or not." -</p> - -<p>Comments to the new wording:</p> - -<p> -a) "Places" has no special meaning, and the everyday language meaning -should fit. -b) The corresponding conditions were negated compared to the current -wording, becaue the new wording requires it. -c) The wording "of the original range" might be redundant, since any -subrange starting at 'first' and containing no more elements than the -original range is implicitly a subrange of the original range [first, -last). -d) The iterator k was introduced instead of "return value" in order to -avoid a cyclic dependency on 25.2.7/3. The wording ", where k shall -denote a value of type ForwardIterator" might be redundant, because it -follows implicitly by 25.2.7/3. -e) "Places" does, in the author's opinion, explicitly forbid duplicating -any element holding the corresponding condition in the original range -[first, last) within the resulting range [first, k). If there is doubt -this term might be not unambiguous regarding this, it is suggested that -k is specified more closely by the following wording: "k shall denote a -value of type ForwardIterator [Note: see d)] so that k - first is equal -to the number of elements in the original range [first, last) for which -the corresponding condition did hold". This could also be expressed as a -separate paragraph "Postcondition:" -f) The senctence "It is undefined whether any elements in the resulting -subrange [k, last) will hold the corresponding condition, or not." was -added consciously so the term "Places" does not imply if the original -range [first, last) contains n elements holding the corresponding -condition, the identical range[first, last) will also contain exactly n -elements holding the corresponding condition after application of the -algorithm. -</p> - -<p> -Change 25.2.7 [lib.alg.remove], paragraph 3 to: - -"Returns: The iterator k." -</p> - -<p> -Change 25.2.7 [lib.alg.remove], paragraph 4 to: - -"Notes: Stable: the relative order of the elements that are placed into -the subrange [first, return value) shall be the same as their relative -order was in the original range [first, last) prior to application of -the algorithm." -</p> - -<p> -Comments to the new wording: -</p> - -<p> -a) the wording "was ... prior to application of the algorithm" is used -to explicitly distinguish the original range not only by means of -iterators, but also by a 'chronological' factor from the resulting range -[first, return value). It might be redundant. -</p> - -<p> -[1]: -The wording of these references is not always unambiguous, and provided -examples partially contradict verbal description of the algorithms, -because the verbal description resembles the problematic wording of -ISO/IEC 14882:2003. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>The LWG believes that the standard is sufficiently clear, and that - there is no evidence of any real-world confusion about this point.</p> - - - - - -<hr> -<h3><a name="490"></a>490. std::unique wrongly specified</h3> -<p><b>Section:</b> 25.3.9 [alg.unique] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thomas Mang <b>Opened:</b> 2004-12-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.unique">issues</a> in [alg.unique].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>In Section 25.2.8 [lib.alg.unique], paragraphs 1 to 3 describe the -behavior of the mutating sequence operation std::unique. However, the -wording does not reflect the intended behavior [Note: See definition of -intended behavior below] of these algorithms, as it is known to the C++ -community [1].</p> - - - -<p>1) Analysis of current wording:</p> - - -<p>25.2.8 [lib.alg.unique], paragraph 1:</p> - -<p> -Current wording says: -"Effects: Eliminates all but the first element from every consecutive -group of equal elements referred to by the iterator i in the range -[first, last) for which the following corresponding conditions hold: *i -== *(i - 1) or pred(*i, *(i -1)) != false" -</p> - -<p> -This sentences expresses specifically that all elements denoted by the -(original) range [first, last) which are not but the first element from -a consecutive group of equal elements (where equality is defined as *i -== *(i - 1) or pred(*i, *(i - 1)) ! = false) [Note: See DR 202], call -them r-elements [Note: r...remove], will be eliminated. Since there is -no formal definition of the term "eliminate" provided, it is undefined -how this "elimination" takes place. But the meaning of "eliminate" in -everyday language seems to disallow explicitly that after application of -the algorithm, any r-element will remain at any position of the range -[first, last) [2]. -</p> - -<p> -Another defect in the current wording concerns the iterators used to -compare two elements for equality: The current wording contains the -expression "(i - 1)", which is not covered by 25/9 [Note: See DR -submitted by Thomas Mang regarding invalid iterator arithmetic -expressions]. -</p> - - -<p> -25.2.8 [lib.alg.unique], paragraph 2: -</p> -<p>Current wording says: -"Returns: The end of the resulting range."</p> - -<p> -The resulting range is not specified. In combination with 25.2.8 -[lib.alg.unique], paragraph 1, one reasonable interpretation (in the -author's opinion even the only possible interpretation) of this -so-called resulting range is the range [first, last) - thus returning -always the ForwardIterator 'last' parameter. -</p> - -<p>2) Description of intended behavior:</p> - -<p> -For the rest of this Defect Report, it is assumed that the intended -behavior was that all elements denoted by the original range [first, -last) which are the first element from a consecutive group of elements -for which the corresponding conditions: *(i-1) == *i (for the version of -unique without a predicate argument) or pred(*(i-1), *i) ! = false (for -the version of unique with a predicate argument) [Note: If such a group -of elements consists of only a single element, this is also considered -the first element] [Note: See resolutions of DR 202], call them -s-elements [Note: s...stay], will be placed into a contiguous subrange -of [first, last), denoted by the iterators [first, return value). The -number of elements in the resulting range [first, return value) shall be -equal to the number of s-elements in the original range [first, last). -Invalid iterator arithmetic expressions are expected to be resolved as -proposed in DR submitted by Thomas Mang regarding invalid iterator -arithmetic expressions. It is also assumed by the author that the -relative order of the elements in the resulting subrange [first, return -value) shall be the same as the relative order of the corresponding -elements (the s-elements) in the original range [Note: If this was not -intended behavior, the additional proposed paragraph about stable order -will certainly become obsolete]. -Furthermore, the resolutions of DR 202 are partially considered. -</p> - -<p> -All implementations known to the author of this Defect Report comply -with this intent [Note: Except possible effects of DR 202]. Since this -intent of the behavior (contrary to the current wording) is also -described in various utility references serving the C++ community [1], -it is not expected that fixing the paragraphs will influence current -code [Note: Except possible effects of DR 202] - unless the code relies -on the behavior as it is described by current wording and the -implementation indeed reflects the current wording, and not the intent. -</p> - - - -<p>3) Proposed fixes:</p> - -<p> -Change 25.2.8 [lib.alg.unique], paragraph 1 to: -</p> - -<p> -"Effect: Places the first element from every consecutive group of -elements, referred to by the iterator i in the range [first, last), for -which the following conditions hold: *(i-1) == *i (for the version of -unique without a predicate argument) or pred(*(i -1), *i) != false (for -the version of unique with a predicate argument), into the subrange -[first, k) of the original range, where k shall denote a value of type -ForwardIterator." -</p> - -<p>Comments to the new wording:</p> - -<p> -a) The new wording was influenced by the resolutions of DR 202. If DR -202 is resolved in another way, the proposed wording need also -additional review. -b) "Places" has no special meaning, and the everyday language meaning -should fit. -c) The expression "(i - 1)" was left, but is expected that DR submitted -by Thomas Mang regarding invalid iterator arithmetic expressions will -take this into account. -d) The wording "(for the version of unique without a predicate -argument)" and "(for the version of unique with a predicate argument)" -was added consciously for clarity and is in resemblence with current -23.2.2.4 [lib.list.ops], paragraph 19. It might be considered redundant. -e) The wording "of the original range" might be redundant, since any -subrange starting at first and containing no more elements than the -original range is implicitly a subrange of the original range [first, -last). -f) The iterator k was introduced instead of "return value" in order to -avoid a cyclic dependency on 25.2.8 [lib.alg.unique], paragraph 2. The -wording ", where k shall denote a value of type ForwardIterator" might -be redundant, because it follows implicitly by 25.2.8 [lib.alg.unique], -paragraph 2. -g) "Places" does, in the author's opinion, explicitly forbid duplicating -any s-element in the original range [first, last) within the resulting -range [first, k). If there is doubt this term might be not unambiguous -regarding this, it is suggested that k is specified more closely by the -following wording: "k shall denote a value of type ForwardIterator -[Note: See f)] so that k - first is equal to the number of elements in -the original range [first, last) being the first element from every -consecutive group of elements for which the corresponding condition did -hold". This could also be expressed as a separate paragraph -"Postcondition:". -h) If it is considered that the wording is unclear whether it declares -the element of a group which consists of only a single element -implicitly to be the first element of this group [Note: Such an -interpretation could eventually arise especially in case last - first == -1] , the following additional sentence is proposed: "If such a group of -elements consists of only a single element, this element is also -considered the first element." -</p> - -<p> -Change 25.2.8 [lib.alg.unique], paragraph 2 to: -"Returns: The iterator k." -</p> - -<p> -Add a separate paragraph "Notes:" as 25.2.8 [lib.alg.unique], paragraph -2a or 3a, or a separate paragraph "Postcondition:" before 25.2.8 -[lib.alg.unique], paragraph 2 (wording inside {} shall be eliminated if -the preceding expressions are used, or the preceding expressions shall -be eliminated if wording inside {} is used): -</p> - -<p> -"Notes:{Postcondition:} Stable: the relative order of the elements that -are placed into the subrange [first, return value {k}) shall be the same -as their relative order was in the original range [first, last) prior to -application of the algorithm." -</p> - -<p>Comments to the new wording:</p> - -<p> -a) It is assumed by the author that the algorithm was intended to be -stable. -In case this was not the intent, this paragraph becomes certainly -obsolete. -b) The wording "was ... prior to application of the algorithm" is used -to explicitly distinguish the original range not only by means of -iterators, but also by a 'chronological' factor from the resulting range -[first, return value). It might be redundant. -</p> - -<p> -25.2.8 [lib.alg.unique], paragraph 3: -</p> -<p>See DR 239.</p> - -<p> -4) References to other DRs: -</p> - -<p> -See DR 202, but which does not address any of the problems described in -this Defect Report [Note: This DR is supposed to complement DR 202]. -See DR 239. -See DR submitted by Thomas Mang regarding invalid iterator arithmetic -expressions. -</p> - -<p> -[1]: -The wording of these references is not always unambiguous, and provided -examples partially contradict verbal description of the algorithms, -because the verbal description resembles the problematic wording of -ISO/IEC 14882:2003. -</p> - -<p> -[2]: -Illustration of conforming implementations according to current wording: -</p> - -<p> -One way the author of this DR considers how this "elimination" could be -achieved by a conforming implementation according to current wording is -by substituting each r-element by _any_ s-element [Note: s...stay; any -non-r-element], since all r-elements are "eliminated". -</p> - -<p> -In case of a sequence consisting of elements being all 'equal' [Note: -See DR 202], substituting each r-element by the single s-element is the -only possible solution according to current wording. -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>The LWG believes the standard is sufficiently clear. No -implementers get it wrong, and changing it wouldn't cause any code to -change, so there is no real-world harm here.</p> - - - - - -<hr> -<h3><a name="491"></a>491. std::list<>::unique incorrectly specified</h3> -<p><b>Section:</b> 23.3.5.5 [list.ops] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thomas Mang <b>Opened:</b> 2004-12-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#list.ops">issues</a> in [list.ops].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>In Section 23.3.5.5 [list.ops], paragraphs 19 to 21 describe the -behavior of the std::list<T, Allocator>::unique operation. However, the -current wording is defective for various reasons.</p> - - - -<p> -1) Analysis of current wording: -</p> - -<p>23.3.5.5 [list.ops], paragraph 19:</p> - -<p> -Current wording says: -"Effects: Eliminates all but the first element from every consecutive -group of equal elements referred to by the iterator i in the range -[first + 1, last) for which *i == *(i - 1) (for the version of unique -with no argument) or pred(*i, *(i -1)) (for the version of unique with a -predicate argument) holds."</p> - -<p> -This sentences makes use of the undefined term "Eliminates". Although it -is, to a certain degree, reasonable to consider the term "eliminate" -synonymous with "erase", using "Erase" in the first place, as the -wording of 23.3.5.5 [list.ops], paragraph 15 does, would be clearer.</p> - -<p> -The range of the elements referred to by iterator i is "[first + 1, -last)". However, neither "first" nor "last" is defined.</p> - -<p> -The sentence makes three times use of iterator arithmetic expressions ( -"first + 1", "*i == *(i - 1)", "pred(*i, *(i -1))" ) which is not -defined for bidirectional iterator [see DR submitted by Thomas Mang -regarding invalid iterator arithmetic expressions].</p> - -<p> -The same problems as pointed out in DR 202 (equivalence relation / order -of arguments for pred()) apply to this paragraph.</p> - -<p> -23.3.5.5 [list.ops], paragraph 20: -</p> - -<p> -Current wording says: -"Throws: Nothing unless an exception in thrown by *i == *(i-1) or -pred(*i, *(i - 1))"</p> - -<p> -The sentence makes two times use of invalid iterator arithmetic -expressions ( "*i == *(i - 1)", "pred(*i, *(i -1))" ). -</p> -<p> -[Note: Minor typos: "in" / missing dot at end of sentence.] -</p> - -<p> -23.3.5.5 [list.ops], paragraph 21:</p> - -<p> -Current wording says: -"Complexity: If the range (last - first) is not empty, exactly (last - -first) - 1 applications of the corresponding predicate, otherwise no -application of the predicate.</p> - -<p> -See DR 315 regarding "(last - first)" not yielding a range.</p> - -<p> -Invalid iterator arithmetic expression "(last - first) - 1" left .</p> - - -<p>2) Description of intended behavior:</p> - -<p> -For the rest of this Defect Report, it is assumed that "eliminate" is -supposed to be synonymous to "erase", that "first" is equivalent to an -iterator obtained by a call to begin(), "last" is equivalent to an -iterator obtained by a call to end(), and that all invalid iterator -arithmetic expressions are resolved as described in DR submitted by -Thomas Mang regarding invalid iterator arithmetic expressions.</p> - -<p> -Furthermore, the resolutions of DR 202 are considered regarding -equivalence relation and order of arguments for a call to pred.</p> - -<p> -All implementations known to the author of this Defect Report comply -with these assumptions, apart from the impact of the alternative -resolution of DR 202. Except for the changes implied by the resolutions -of DR 202, no impact on current code is expected.</p> - -<p> -3) Proposed fixes:</p> - -<p> -Change 23.3.5.5 [list.ops], paragraph 19 to:</p> - -<p> -"Effect: Erases all but the first element from every consecutive group -of elements, referred to by the iterator i in the range [begin(), -end()), for which the following conditions hold: *(i-1) == *i (for the -version of unique with no argument) or pred(*(i-1), *i) != false (for -the version of unique with a predicate argument)."</p> - -<p> -Comments to the new wording:</p> - -<p> -a) The new wording was influenced by DR 202 and the resolutions -presented there. If DR 202 is resolved in another way, the proposed -wording need also additional review. -b) "Erases" refers in the author's opinion unambiguously to the member -function "erase". In case there is doubt this might not be unamgibuous, -a direct reference to the member function "erase" is suggested [Note: -This would also imply a change of 23.3.5.5 [list.ops], paragraph -15.]. -c) The expression "(i - 1)" was left, but is expected that DR submitted -by Thomas Mang regarding invalid iterator arithmetic expressions will -take this into account. -d) The wording "(for the version of unique with no argument)" and "(for -the version of unique with a predicate argument)" was kept consciously -for clarity. -e) "begin()" substitutes "first", and "end()" substitutes "last". The -range need adjustment from "[first + 1, last)" to "[begin(), end())" to -ensure a valid range in case of an empty list. -f) If it is considered that the wording is unclear whether it declares -the element of a group which consists of only a single element -implicitly to be the first element of this group [Note: Such an -interpretation could eventually arise especially in case size() == 1] , -the following additional sentence is proposed: "If such a group of -elements consists of only a single element, this element is also -considered the first element."</p> - -<p> -Change 23.3.5.5 [list.ops], paragraph 20 to:</p> - -<p> -"Throws: Nothing unless an exception is thrown by *(i-1) == *i or -pred(*(i-1), *i)."</p> - -<p> -Comments to the new wording:</p> - -<p> -a) The wording regarding the conditions is identical to proposed -23.3.5.5 [list.ops], paragraph 19. If 23.3.5.5 [list.ops], -paragraph 19 is resolved in another way, the proposed wording need also -additional review. -b) The expression "(i - 1)" was left, but is expected that DR submitted -by Thomas Mang regarding invalid iterator arithmetic expressions will -take this into account. -c) Typos fixed.</p> - -<p> -Change 23.3.5.5 [list.ops], paragraph 21 to:</p> - -<p> -"Complexity: If empty() == false, exactly size() - 1 applications of the -corresponding predicate, otherwise no applications of the corresponding -predicate."</p> - -<p> -Comments to the new wording:</p> - -<p> -a) The new wording is supposed to also replace the proposed resolution -of DR 315, which suffers from the problem of undefined "first" / "last". -</p> - -<p> -5) References to other DRs:</p> - -<p>See DR 202. -See DR 239. -See DR 315. -See DR submitted by Thomas Mang regarding invalid iterator arithmetic -expressions.</p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>"All implementations known to the author of this Defect Report -comply with these assumption", and "no impact on current code is -expected", i.e. there is no evidence of real-world confusion or -harm.</p> - - - - - -<hr> -<h3><a name="492"></a>492. Invalid iterator arithmetic expressions</h3> -<p><b>Section:</b> 17.5.1.4 [structure.specifications] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thomas Mang <b>Opened:</b> 2004-12-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#structure.specifications">issues</a> in [structure.specifications].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>Various clauses other than clause 25 make use of iterator arithmetic not -supported by the iterator category in question. -Algorithms in clause 25 are exceptional because of 25 [lib.algorithms], -paragraph 9, but this paragraph does not provide semantics to the -expression "iterator - n", where n denotes a value of a distance type -between iterators.</p> - -<p>1) Examples of current wording:</p> - -<p>Current wording outside clause 25:</p> - -<p> -23.2.2.4 [lib.list.ops], paragraphs 19-21: "first + 1", "(i - 1)", -"(last - first)" -23.3.1.1 [lib.map.cons], paragraph 4: "last - first" -23.3.2.1 [lib.multimap.cons], paragraph 4: "last - first" -23.3.3.1 [lib.set.cons], paragraph 4: "last - first" -23.3.4.1 [lib.multiset.cons], paragraph 4: "last - first" -24.4.1 [lib.reverse.iterators], paragraph 1: "(i - 1)" -</p> - -<p> -[Important note: The list is not complete, just an illustration. The -same issue might well apply to other paragraphs not listed here.]</p> - -<p>None of these expressions is valid for the corresponding iterator -category.</p> - -<p>Current wording in clause 25:</p> - -<p> -25.1.1 [lib.alg.foreach], paragraph 1: "last - 1" -25.1.3 [lib.alg.find.end], paragraph 2: "[first1, last1 - -(last2-first2))" -25.2.8 [lib.alg.unique], paragraph 1: "(i - 1)" -25.2.8 [lib.alg.unique], paragraph 5: "(i - 1)" -</p> - -<p> -However, current wording of 25 [lib.algorithms], paragraph 9 covers -neither of these four cases:</p> - -<p>Current wording of 25 [lib.algorithms], paragraph 9:</p> - -<p> -"In the description of the algorithms operator + and - are used for some -of the iterator categories for which they do not have to be defined. In -these cases the semantics of a+n is the same as that of</p> -<pre> -{X tmp = a; -advance(tmp, n); -return tmp; -} -</pre> -<p>and that of b-a is the same as of return distance(a, b)"</p> - -<p> -This paragrpah does not take the expression "iterator - n" into account, -where n denotes a value of a distance type between two iterators [Note: -According to current wording, the expression "iterator - n" would be -resolved as equivalent to "return distance(n, iterator)"]. Even if the -expression "iterator - n" were to be reinterpreted as equivalent to -"iterator + -n" [Note: This would imply that "a" and "b" were -interpreted implicitly as values of iterator types, and "n" as value of -a distance type], then 24.3.4/2 interfers because it says: "Requires: n -may be negative only for random access and bidirectional iterators.", -and none of the paragraphs quoted above requires the iterators on which -the algorithms operate to be of random access or bidirectional category. -</p> - -<p>2) Description of intended behavior:</p> - -<p> -For the rest of this Defect Report, it is assumed that the expression -"iterator1 + n" and "iterator1 - iterator2" has the semantics as -described in current 25 [lib.algorithms], paragraph 9, but applying to -all clauses. The expression "iterator1 - n" is equivalent to an -result-iterator for which the expression "result-iterator + n" yields an -iterator denoting the same position as iterator1 does. The terms -"iterator1", "iterator2" and "result-iterator" shall denote the value of -an iterator type, and the term "n" shall denote a value of a distance -type between two iterators.</p> - -<p> -All implementations known to the author of this Defect Report comply -with these assumptions. -No impact on current code is expected.</p> - -<p>3) Proposed fixes:</p> - - -<p>Change 25 [lib.algorithms], paragraph 9 to:</p> - -<p> -"In the description of the algorithms operator + and - are used for some -of the iterator categories for which they do not have to be defined. In -this paragraph, a and b denote values of an iterator type, and n denotes -a value of a distance type between two iterators. In these cases the -semantics of a+n is the same as that of</p> -<pre> -{X tmp = a; -advance(tmp, n); -return tmp; -} -</pre> -<p>,the semantics of a-n denotes the value of an iterator i for which the -following condition holds: -advance(i, n) == a, -and that of b-a is the same as of -return distance(a, b)". -</p> - -<p>Comments to the new wording:</p> - -<p> -a) The wording " In this paragraph, a and b denote values of an iterator -type, and n denotes a value of a distance type between two iterators." -was added so the expressions "b-a" and "a-n" are distinguished regarding -the types of the values on which they operate. -b) The wording ",the semantics of a-n denotes the value of an iterator i -for which the following condition holds: advance(i, n) == a" was added -to cover the expression 'iterator - n'. The wording "advance(i, n) == a" -was used to avoid a dependency on the semantics of a+n, as the wording -"i + n == a" would have implied. However, such a dependency might well -be deserved. -c) DR 225 is not considered in the new wording. -</p> - -<p> -Proposed fixes regarding invalid iterator arithmetic expressions outside -clause 25:</p> - -<p> -Either -a) Move modified 25 [lib.algorithms], paragraph 9 (as proposed above) -before any current invalid iterator arithmetic expression. In that case, -the first sentence of 25 [lib.algorithms], paragraph 9, need also to be -modified and could read: "For the rest of this International Standard, -...." / "In the description of the following clauses including this -...." / "In the description of the text below ..." etc. - anyways -substituting the wording "algorithms", which is a straight reference to -clause 25. -In that case, 25 [lib.algorithms] paragraph 9 will certainly become -obsolete. -Alternatively, -b) Add an appropiate paragraph similar to resolved 25 [lib.algorithms], -paragraph 9, to the beginning of each clause containing invalid iterator -arithmetic expressions. -Alternatively, -c) Fix each paragraph (both current wording and possible resolutions of -DRs) containing invalid iterator arithmetic expressions separately. -</p> - -<p>5) References to other DRs:</p> - -<p> -See DR 225. -See DR 237. The resolution could then also read "Linear in last - -first". -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Keep open and ask Bill to provide wording. -</p></blockquote> - -<p><i>[ -2009-05-09 Alisdair adds: -]</i></p> - - -<blockquote><p> -This issue is related to <a href="lwg-defects.html#997">997</a>. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -Hinnant: this isn't going to change any user's code or any vendor's implementation. -</p> -<p> -No objection to "NAD without prejudice." If anyone proposes a -resolution, the LWG will consider it. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - -<p><i>[Lillehammer: Minor issue, but real. We have a blanket statement -about this in 25/11. But (a) it should be in 17, not 25; and (b) it's -not quite broad enough, because there are some arithmetic expressions -it doesn't cover. Bill will provide wording.]</i></p> - - - - - - - -<hr> -<h3><a name="493"></a>493. Undefined Expression in Input Iterator Note Title</h3> -<p><b>Section:</b> 24.2.3 [input.iterators] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Chris Jefferson <b>Opened:</b> 2004-12-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#input.iterators">issues</a> in [input.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>1) In 24.1.1/3, the following text is currently present.</p> - -<p>"Note: For input iterators, a==b does not imply ++a=++b (Equality does -not guarantee the substitution property or referential transparency)."</p> - -<p>However, when in Table 72, part of the definition of ++r is given as:</p> - -<p>"pre: r is dereferenceable. -post: any copies of the previous value of r are no longer required -either to be dereferenceable ..."</p> - -<p>While a==b does not imply that b is a copy of a, this statement should -perhaps still be made more clear.</p> - -<p>2) There are no changes to intended behaviour</p> - -<p> -3) This Note should be altered to say "Note: For input iterators a==b, -when its behaviour is defined ++a==++b may still be false (Equality does -not guarantee the substitution property or referential transparency).</p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>This is descriptive text, not normative, and the meaning is clear.</p> - - - - - -<hr> -<h3><a name="494"></a>494. Wrong runtime complexity for associative container's insert and delete</h3> -<p><b>Section:</b> 23.2.4 [associative.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Hans B os <b>Opened:</b> 2004-12-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>According to [lib.associative.reqmts] table 69, the runtime comlexity -of insert(p, t) and erase(q) can be done in amortized constant time.</p> - -<p>It was my understanding that an associative container could be -implemented as a balanced binary tree.</p> - -<p>For inser(p, t), you 'll have to iterate to p's next node to see if t -can be placed next to p. Furthermore, the insertion usually takes -place at leaf nodes. An insert next to the root node will be done at -the left of the root next node</p> - -<p>So when p is the root node you 'll have to iterate from the root to -its next node, which takes O(log(size)) time in a balanced tree.</p> - -<p>If you insert all values with insert(root, t) (where root is the -root of the tree before insertion) then each insert takes O(log(size)) -time. The amortized complexity per insertion will be O(log(size)) -also.</p> - -<p>For erase(q), the normal algorithm for deleting a node that has no -empty left or right subtree, is to iterate to the next (or previous), -which is a leaf node. Then exchange the node with the next and delete -the leaf node. Furthermore according to DR 130, erase should return -the next node of the node erased. Thus erasing the root node, -requires iterating to the next node.</p> - -<p>Now if you empty a map by deleting the root node until the map is -empty, each operation will take O(log(size)), and the amortized -complexity is still O(log(size)).</p> - -<p>The operations can be done in amortized constant time if iterating -to the next node can be done in (non amortized) constant time. This -can be done by putting all nodes in a double linked list. This -requires two extra links per node. To me this is a bit overkill since -you can already efficiently insert or erase ranges with erase(first, -last) and insert(first, last).</p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p>Only "amortized constant" in special circumstances, and we believe - that's implementable. That is: doing this N times will be O(N), not - O(log N).</p> - - - - - -<hr> -<h3><a name="499"></a>499. Std. doesn't seem to require stable_sort() to be stable!</h3> -<p><b>Section:</b> 25.4.1.2 [stable.sort] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Prateek Karandikar <b>Opened:</b> 2005-04-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<blockquote><p> -17.3.1.1 Summary</p> - -<p> -1 The Summary provides a synopsis of the category, and introduces the -first-level subclauses. Each subclause also provides a summary, listing -the headers specified in the subclause and the library entities -provided in each header. -</p> -<p> -2 Paragraphs labelled "Note(s):" or "Example(s):" are informative, -other paragraphs are normative. -</p></blockquote> - -<p>So this means that a "Notes" paragraph wouldn't be normative. </p> - -<blockquote><p> -25.3.1.2 stable_sort -</p> -<pre> -template<class RandomAccessIterator> -void stable_sort(RandomAccessIterat or first, RandomAccessIterator last); - -template<class RandomAccessIterator, class Compare> -void stable_sort(RandomAccessIterat or first, RandomAccessIterator last, Compare comp); -</pre> -<p> -1 Effects: Sorts the elements in the range [first, last). -</p> -<p> -2 Complexity: It does at most N(log N)^2 (where N == last - first) -comparisons; if enough extra memory is available, it is N log N. -</p> -<p> -3 Notes: Stable: the relative order of the equivalent elements is -preserved. -</p></blockquote> - -<p> -The Notes para is informative, and nowhere else is stability mentioned above. -</p> - -<p> -Also, I just searched for the word "stable" in my copy of the Standard. -and the phrase "Notes: Stable: the relative order of the elements..." -is repeated several times in the Standard library clauses for -describing various functions. How is it that stability is talked about -in the informative paragraph? Or am I missing something obvious? -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p> -<p> -This change has already been made. -</p> - - - - - -<hr> -<h3><a name="500"></a>500. do_length cannot be implemented correctly</h3> -<p><b>Section:</b> 22.4.1.5 [locale.codecvt.byname] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Krzysztof Żelechowski <b>Opened:</b> 2005-05-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt.byname">issues</a> in [locale.codecvt.byname].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<ol> -<li>codecvt::do_length is of type int;</li> -<li>it is assumed to be sort-of returning from_next - from of type ptrdiff_t;</li> -<li>ptrdiff_t cannot be cast to an int without data loss.</li> -</ol> -<p> -Contradiction. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="501"></a>501. Proposal: strengthen guarantees of lib.comparisons</h3> -<p><b>Section:</b> X [depr.base] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Me <anti_spam_email2003@yahoo.com> <b>Opened:</b> 2005-06-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#depr.base">issues</a> in [depr.base].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<blockquote><p> -"For templates greater, less, greater_equal, and less_equal, -the specializations for any pointer type yield a total order, even if -the built-in operators <, >, <=, >= do not." -</p></blockquote> - -<p> -The standard should do much better than guarantee that these provide a -total order, it should guarantee that it can be used to test if memory -overlaps, i.e. write a portable memmove. You can imagine a platform -where the built-in operators use a uint32_t comparison (this tests for -overlap on this platform) but the less<T*> functor is allowed to be -defined to use a int32_t comparison. On this platform, if you use -std::less with the intent of making a portable memmove, comparison on -an array that straddles the 0x7FFFFFFF/0x8000000 boundary can give -incorrect results. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add a footnote to 20.5.3/8 saying: -</p> - -<blockquote><p> -Given a p1 and p2 such that p1 points to N objects of type T and p2 -points to M objects of type T. If [p1,p1+N) does not overlap [p2,p2+M), -less returns the same value when comparing all pointers in [p1,p1+N) to -all pointers in [p2,p2+M). Otherwise, there is a value Q and a value R -such that less returns the same value when comparing all pointers in -[p1,p1+Q) to all pointers in [p2,p2+R) and an opposite value when -comparing all pointers in [p1+Q,p1+N) to all pointers in [p2+R,p2+M). -For the sake of completeness, the null pointer value (4.10) for T is -considered to be an array of 1 object that doesn't overlap with any -non-null pointer to T. less_equal, greater, greater_equal, equal_to, -and not_equal_to give the expected results based on the total ordering -semantics of less. For T of void, treat it as having similar semantics -as T of char i.e. less<cv T*>(a, b) gives the same results as less<cv -void*>(a, b) which gives the same results as less<cv char*>((cv -char*)(cv void*)a, (cv char*)(cv void*)b). -</p></blockquote> - -<p> -I'm also thinking there should be a footnote to 20.5.3/1 saying that if -A and B are similar types (4.4/4), comp<A>(a,b) returns the same value -as comp<B>(a,b) (where comp is less, less_equal, etc.). But this might -be problematic if there is some really funky operator overloading going -on that does different things based on cv (that should be undefined -behavior if somebody does that though). This at least should be -guaranteed for all POD types (especially pointers) that use the -built-in comparison operators. -</p> - - - -<p><b>Rationale:</b></p> -<p> -less is already required to provide a strict weak ordering which is good enough -to detect overlapping memory situations. -</p> - - - - - -<hr> -<h3><a name="502"></a>502. Proposition: Clarification of the interaction between a facet and an iterator</h3> -<p><b>Section:</b> 22.3.1.1.1 [locale.category] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Christopher Conrade Zseleghovski <b>Opened:</b> 2005-06-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.category">issues</a> in [locale.category].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Motivation: -</p> - -<p> -This requirement seems obvious to me, it is the essence of code modularity. -I have complained to Mr. Plauger that the Dinkumware library does not -observe this principle but he objected that this behaviour is not covered in -the standard. -</p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -No objection to NAD, Fixed. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Append the following point to 22.1.1.1.1: -</p> - -<p> -6. The implementation of a facet of Table 52 parametrized with an -InputIterator/OutputIterator should use that iterator only as character -source/sink respectively. -For a *_get facet, it means that the value received depends only on the -sequence of input characters and not on how they are accessed. -For a *_put facet, it means that the sequence of characters output depends -only on the value to be formatted and not of how the characters are stored. -</p> - -<p><i>[ -Berlin: Moved to Open, Need to clean up this area to make it clear -locales don't have to contain open ended sets of facets. Jack, Howard, -Bill. -]</i></p> - - - - - - - -<hr> -<h3><a name="503"></a>503. more on locales</h3> -<p><b>Section:</b> 22.4 [locale.categories] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2005-06-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.categories">issues</a> in [locale.categories].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -a) In 22.2.1.1 para. 2 we refer to "the instantiations required in Table -51" to refer to the facet *objects* associated with a locale. And we -almost certainly mean just those associated with the default or "C" -locale. Otherwise, you can't switch to a locale that enforces a different -mapping between narrow and wide characters, or that defines additional -uppercase characters. -</p> - -<p> -b) 22.2.1.5 para. 3 (codecvt) has the same issues. -</p> - -<p> -c) 22.2.1.5.2 (do_unshift) is even worse. It *forbids* the generation of -a homing sequence for the basic character set, which might very well need -one. -</p> - -<p> -d) 22.2.1.5.2 (do_length) likewise dictates that the default mapping -between wide and narrow characters be taken as one-for-one. -</p> - -<p> -e) 22.2.2 para. 2 (num_get/put) is both muddled and vacuous, as far as -I can tell. The muddle is, as before, calling Table 51 a list of -instantiations. But the constraint it applies seems to me to cover -*all* defined uses of num_get/put, so why bother to say so? -</p> - -<p> -f) 22.2.3.1.2 para. 1(do_decimal_point) says "The required instantiations -return '.' or L'.'.) Presumably this means "as appropriate for the -character type. But given the vague definition of "required" earlier, -this overrules *any* change of decimal point for non "C" locales. -Surely we don't want to do that. -</p> - -<p> -g) 22.2.3.1.2 para. 2 (do_thousands_sep) says "The required instantiations -return ',' or L','.) As above, this probably means "as appropriate for the -character type. But this overrules the "C" locale, which requires *no* -character ('\0') for the thousands separator. Even if we agree that we -don't mean to block changes in decimal point or thousands separator, -we should also eliminate this clear incompatibility with C. -</p> - -<p> -h) 22.2.3.1.2 para. 2 (do_grouping) says "The required instantiations -return the empty string, indicating no grouping." Same considerations -as for do_decimal_point. -</p> - -<p> -i) 22.2.4.1 para. 1 (collate) refers to "instantiations required in Table -51". Same bad jargon. -</p> - -<p> -j) 22.2.4.1.2 para. 1 (do_compare) refers to "instantiations required -in Table 51". Same bad jargon. -</p> - -<p> -k) 22.2.5 para. 1 (time_get/put) uses the same muddled and vacuous -as num_get/put. -</p> - -<p> -l) 22.2.6 para. 2 (money_get/put) uses the same muddled and vacuous -as num_get/put. -</p> - -<p> -m) 22.2.6.3.2 (do_pos/neg_format) says "The instantiations required -in Table 51 ... return an object of type pattern initialized to -{symbol, sign, none, value}." This once again *overrides* the "C" -locale, as well as any other locale." -</p> - -<p> -3) We constrain the use_facet calls that can be made by num_get/put, -so why don't we do the same for money_get/put? Or for any of the -other facets, for that matter? -</p> - -<p> -4) As an almost aside, we spell out when a facet needs to use the ctype -facet, but several also need to use a codecvt facet and we don't say so. -</p> -<p><i>[ -Berlin: Bill to provide wording. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -No objection to NAD. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="504"></a>504. Integer types in pseudo-random number engine requirements</h3> -<p><b>Section:</b> 26.5.1 [rand.req], TR1 5.1.1 [tr.rand.req] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.req">issues</a> in [rand.req].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In [tr.rand.req], Paragraph 2 states that "... s is a value of integral type, -g is an ... object returning values of unsigned integral type ..." -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In 5.1.1 [tr.rand.req], Paragraph 2 replace -</p> - -<blockquote><p> -... s is a value of integral type, g is an lvalue of a type other than X that -defines a zero-argument function object returning values of <del>unsigned integral</del> type -<ins><tt>unsigned long int</tt></ins>, -... -</p></blockquote> - -<p> -In 5.1.1 [tr.rand.seq], Table 16, replace in the line for X(s) -</p> - -<blockquote><p> -creates an engine with the initial internal state -determined by <ins><tt>static_cast<unsigned long>(</tt></ins><tt><i>s</i></tt><ins><tt>)</tt></ins> -</p></blockquote> - -<p><i>[ -Mont Tremblant: Both s and g should be unsigned long. -This should refer to the constructor signatures. Jens provided wording post Mont Tremblant. -]</i></p> - - -<p><i>[ -Berlin: N1932 adopts the proposed resolution: see 26.3.1.3/1e and Table 3 row 2. Moved -to Ready. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -Jens: Just requiring X(unsigned long) still makes it possible -for an evil library writer to also supply a X(int) that does something -unexpected. The wording above requires that X(s) always performs -as if X(unsigned long) would have been called. I believe that is -sufficient and implements our intentions from Mont Tremblant. I -see no additional use in actually requiring a X(unsigned long) -signature. u.seed(s) is covered by its reference to X(s), same -arguments. -</p> - - -<p><i>[ -Portland: Subsumed by N2111. -]</i></p> - - - - - -<hr> -<h3><a name="506"></a>506. Requirements of Distribution parameter for variate_generator</h3> -<p><b>Section:</b> 26.5 [rand], TR1 5.1.3 [tr.rand.var] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand">issues</a> in [rand].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Paragraph 3 requires that template argument U (which corresponds to template -parameter Engine) satisfy all uniform random number generator requirements. -However, there is no analogous requirement regarding the template argument -that corresponds to template parameter Distribution. We believe there should -be, and that it should require that this template argument satisfy all random -distribution requirements. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Consequence 1: Remove the precondition clauses [tr.rand.var]/16 and /18. -</p> -<p> -Consequence 2: Add max() and min() functions to those distributions that -do not already have them. -</p> - -<p><i>[ -Mont Tremblant: Jens reccommends NAD, min/max not needed everywhere. -Marc supports having min and max to satisfy generic programming interface. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p>Berlin: N1932 makes this moot: variate_generator has been eliminated.</p> - - - - - -<hr> -<h3><a name="509"></a>509. Uniform_int template parameters</h3> -<p><b>Section:</b> 26.5.8.2 [rand.dist.uni], TR1 5.1.7.1 [tr.rand.dist.iunif] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.dist.uni">issues</a> in [rand.dist.uni].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In [tr.rand.dist.iunif] the uniform_int distribution currently has a single -template parameter, IntType, used as the input_type and as the result_type -of the distribution. We believe there is no reason to conflate these types -in this way. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -We recommend that there be a second template parameter to -reflect the distribution's input_type, and that the existing first template -parameter continue to reflect (solely) the result_type: -</p> -<blockquote><pre> -template< class IntType = int, UIntType = unsigned int > -class uniform_int -{ -public: - // types - typedef UIntType input_type; - typedef IntType result_type; -</pre></blockquote> - -<p><i>[ -Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been -eliminated. -]</i></p> - - - - - - - -<hr> -<h3><a name="510"></a>510. Input_type for bernoulli_distribution</h3> -<p><b>Section:</b> 26.5.8.3 [rand.dist.bern], TR1 5.1.7.2 [tr.rand.dist.bern] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In [tr.rand.dist.bern] the distribution currently requires; -</p> -<blockquote><pre> -typedef int input_type; -</pre></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -We believe this is an unfortunate choice, and recommend instead: -</p> -<blockquote><pre> -typedef unsigned int input_type; -</pre></blockquote> - -<p><i>[ -Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been -eliminated. -]</i></p> - - - - - - - -<hr> -<h3><a name="511"></a>511. Input_type for binomial_distribution</h3> -<p><b>Section:</b> 26.5.8 [rand.dist], TR1 5.1.7.5 [tr.rand.dist.bin] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.dist">issues</a> in [rand.dist].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Unlike all other distributions in TR1, this binomial_distribution has an -implementation-defined input_type. We believe this is an unfortunate choice, -because it hinders users from writing portable code. It also hinders the -writing of compliance tests. We recommend instead: -</p> -<blockquote><pre> -typedef RealType input_type; -</pre></blockquote> -<p> -While this choice is somewhat arbitrary (as it was for some of the other -distributions), we make this particular choice because (unlike all other -distributions) otherwise this template would not publish its RealType -argument and so users could not write generic code that accessed this -second template parameter. In this respect, the choice is consistent with -the other distributions in TR1. -</p> -<p> -We have two reasons for recommending that a real type be specified instead. -One reason is based specifically on characteristics of binomial distribution -implementations, while the other is based on mathematical characteristics of -probability distribution functions in general. -</p> -<p> -Implementations of binomial distributions commonly use Stirling approximations -for values in certain ranges. It is far more natural to use real values to -represent these approximations than it would be to use integral values to do -so. In other ranges, implementations reply on the Bernoulli distribution to -obtain values. While TR1's bernoulli_distribution::input_type is specified as -int, we believe this would be better specified as double. -</p> -<p> -This brings us to our main point: The notion of a random distribution rests -on the notion of a cumulative distribution function, which in turn mathematically -depends on a continuous dependent variable. Indeed, such a distribution function -would be meaningless if it depended on discrete values such as integers - and this -remains true even if the distribution function were to take discrete steps. -</p> -<p> -Although this note is specifically about binomial_distribution::input_type, -we intend to recommend that all of the random distributions input_types be -specified as a real type (either a RealType template parameter, or double, -as appropriate). -</p> -<p> -Of the nine distributions in TR1, four already have this characteristic -(uniform_real, exponential_distribution, normal_distribution, and -gamma_distribution). We have already argued the case for the binomial the -remaining four distributions. -</p> -<p> -In the case of uniform_int, we believe that the calculations to produce an -integer result in a specified range from an integer in a different specified -range is best done using real arithmetic. This is because it involves a -product, one of whose terms is the ratio of the extents of the two ranges. -Without real arithmetic, the results become less uniform: some numbers become -more (or less) probable that they should be. This is, of course, undesireable -behavior in a uniform distribution. -</p> -<p> -Finally, we believe that in the case of the bernoulli_distribution (briefly -mentioned earlier), as well as the cases of the geometric_distribution and the -poisson_distribution, it would be far more natural to have a real input_type. -This is because the most natural computation involves the random number -delivered and the distribution's parameter p (in the case of bernoulli_distribution, -for example, the computation is a comparison against p), and p is already specified -in each case as having some real type. -</p> - - -<p><b>Proposed resolution:</b></p> -<blockquote><pre> -typedef RealType input_type; -</pre></blockquote> - -<p><i>[ -Berlin: Moved to NAD. N1932 makes this moot: the input_type template parameter has been -eliminated. -]</i></p> - - - - - - -<hr> -<h3><a name="512"></a>512. Seeding <tt>subtract_with_carry_01</tt> from a single unsigned long</h3> -<p><b>Section:</b> 26.5.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.eng">issues</a> in [rand.eng].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Paragraph 8 specifies the algorithm by which a <tt>subtract_with_carry_01</tt> engine -is to be seeded given a single unsigned long. This algorithm is seriously -flawed in the case where the engine parameter w (also known as word_size) -exceeds 31 [bits]. The key part of the paragraph reads: -</p> -<blockquote><p> -sets x(-r) ... x(-1) to (lcg(1)*2**(-w)) mod 1 -</p></blockquote> -<p> -and so forth. -</p> -<p> -Since the specified linear congruential engine, lcg, delivers numbers with -a maximum of 2147483563 (just a shade under 31 bits), then when w is, for -example, 48, each of the x(i) will be less than 2**-17. The consequence -is that roughly the first 400 numbers delivered will be conspicuously -close to either zero or one. -</p> -<p> -Unfortunately, this is not an innocuous flaw: One of the predefined engines -in [tr.rand.predef], namely <tt>ranlux64_base_01</tt>, has w = 48 and would exhibit -this poor behavior, while the original N1378 proposal states that these -pre-defined engines are intended to be of "known good properties." -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In 5.1.4.4 [tr.rand.eng.sub1], replace the "effects" clause for -void seed(unsigned long value = 19780503) by -</p> - -<blockquote><p> -<i>Effects:</i> If <tt>value == 0</tt>, sets value to <tt>19780503</tt>. In any -case, <del>with a linear congruential generator <tt>lcg</tt>(i) having parameters -<tt><i>m<sub>lcg</sub></i> = 2147483563</tt>, <tt><i>a<sub>lcg</sub></i> = 40014</tt>, -<tt><i>c<sub>lcg</sub></i> = 0</tt>, and <tt><i>lcg</i>(0) = value</tt>,</del> -sets <ins>carry<tt>(-1)</tt> and</ins> <tt>x(-r) … x(-1)</tt> -<ins>as if executing</ins></p> - -<blockquote><pre><ins> -linear_congruential<unsigned long, 40014, 0, 2147483563> lcg(value); -seed(lcg); -</ins></pre></blockquote> - -<p> -<del>to <tt>(<i>lcg</i>(1) · 2<sup>-<i>w</i></sup>) mod 1 -… (<i>lcg</i>(<i>r</i>) · 2<sup>-<i>w</i></sup>) mod 1</tt>, -respectively. If <tt><i>x</i>(-1) == 0</tt>, sets carry<tt>(-1) = 2<sup>-<i>w</i></sup></tt>, -else sets carry<tt>(-1) = 0</tt>.</del></p> -</blockquote> - -<p><i>[ -Jens provided revised wording post Mont Tremblant. -]</i></p> - - -<p><i>[ -Berlin: N1932 adopts the originally-proposed resolution of the issue. -Jens's supplied wording is a clearer description of what is -intended. Moved to Ready. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -Jens: I'm using an explicit type here, because fixing the -prose would probably not qualify for the (with issue <a href="lwg-closed.html#504">504</a> even -stricter) requirements we have for seed(Gen&). -</p> - -<p><i>[ -Portland: Subsumed by N2111. -]</i></p> - - - - - - -<hr> -<h3><a name="513"></a>513. Size of state for subtract_with_carry_01</h3> -<p><b>Section:</b> 26.5.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.eng">issues</a> in [rand.eng].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Paragraph 3 begins: -</p> -<blockquote><p> -The size of the state is r. -</p></blockquote> -<p> -However, this is not quite consistent with the remainder of the paragraph -which specifies a total of nr+1 items in the textual representation of -the state. We recommend the sentence be corrected to match: -</p> -<blockquote><p> -The size of the state is nr+1. -</p></blockquote> -<p> -To give meaning to the coefficient n, it may be also desirable to move -n's definition from later in the paragraph. Either of the following -seem reasonable formulations: -</p> -<blockquote><p> -With n=..., the size of the state is nr+1. -</p></blockquote> -<blockquote><p> -The size of the state is nr+1, where n=... . -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p><i>[ -Jens: I plead for "NAD" on the grounds that "size of state" is only -used as an argument for big-O complexity notation, thus -constant factors and additions don't count. -]</i></p> - - -<p><i>[ -Berlin: N1932 adopts the proposed NAD. -]</i></p> - - - - - - - -<hr> -<h3><a name="514"></a>514. Size of state for subtract_with_carry</h3> -<p><b>Section:</b> 26.5.3.3 [rand.eng.sub], TR1 5.1.4.3 [tr.rand.eng.sub] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Paragraph 2 begins: -</p> -<blockquote><p> -The size of the state is r. -</p></blockquote> -<p> -However, the next sentence specifies a total of r+1 items in the textual -representation of the state, r specific x's as well as a specific carry. -This makes a total of r+1 items that constitute the size of the state, -rather than r. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -We recommend the sentence be corrected to match: -</p> -<blockquote><p> - The size of the state is r+1. -</p></blockquote> - -<p><i>[ -Jens: I plead for "NAD" on the grounds that "size of state" is only -used as an argument for big-O complexity notation, thus -constant factors and additions don't count. -]</i></p> - - -<p><i>[ -Berlin: N1932 adopts the proposed NAD. -]</i></p> - - - - - - - -<hr> -<h3><a name="515"></a>515. Random number engine traits</h3> -<p><b>Section:</b> 26.5.2 [rand.synopsis], TR1 5.1.2 [tr.rand.synopsis] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.synopsis">issues</a> in [rand.synopsis].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -To accompany the concept of a pseudo-random number engine as defined in Table 17, -we propose and recommend an adjunct template, engine_traits, to be declared in -[tr.rand.synopsis] as: -</p> -<blockquote><pre> -template< class PSRE > -class engine_traits; -</pre></blockquote> -<p> -This template's primary purpose would be as an aid to generic programming involving -pseudo-random number engines. Given only the facilities described in tr1, it would -be very difficult to produce any algorithms involving the notion of a generic engine. -The intent of this proposal is to provide, via engine_traits<>, sufficient -descriptive information to allow an algorithm to employ a pseudo-random number engine -without regard to its exact type, i.e., as a template parameter. -</p> -<p> -For example, today it is not possible to write an efficient generic function that -requires any specific number of random bits. More specifically, consider a -cryptographic application that internally needs 256 bits of randomness per call: -</p> -<blockquote><pre> -template< class Eng, class InIter, class OutIter > -void crypto( Eng& e, InIter in, OutIter out ); -</pre></blockquote> -<p> -Without knowning the number of bits of randomness produced per call to a provided -engine, the algorithm has no means of determining how many times to call the engine. -</p> -<p> -In a new section [tr.rand.eng.traits], we proposed to define the engine_traits -template as: -</p> -<blockquote><pre> -template< class PSRE > -class engine_traits -{ - static std::size_t bits_of_randomness = 0u; - static std::string name() { return "unknown_engine"; } - // TODO: other traits here -}; -</pre></blockquote> -<p> -Further, each engine described in [tr.rand.engine] would be accompanied by a -complete specialization of this new engine_traits template. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p><i>[ -Berlin: Walter: While useful for implementation per TR1, N1932 has no need for this -feature. Recommend close as NAD. -]</i></p> - - - -<p><b>Rationale:</b></p> -<p> -Recommend NAD, -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1932.pdf">N1932</a>, -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2111.pdf">N2111</a> -covers this. Already in WP. -</p> - - - - - -<hr> -<h3><a name="516"></a>516. Seeding subtract_with_carry_01 using a generator</h3> -<p><b>Section:</b> 26.5.3 [rand.eng], TR1 5.1.4.4 [tr.rand.eng.sub1] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.eng">issues</a> in [rand.eng].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Paragraph 6 says: -</p> -<blockquote><p> -... obtained by successive invocations of g, ... -</p></blockquote> -<p> -We recommend instead: -</p> -<blockquote><p> -... obtained by taking successive invocations of g mod 2**32, ... -</p></blockquote> -<p> -as the context seems to require only 32-bit quantities be used here. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Berlin: N1932 adopts the proposed resultion: see 26.3.3.4/7. Moved to Ready. -</p> - -<p><i>[ -Portland: Subsumed by N2111. -]</i></p> - - - - - - -<hr> -<h3><a name="517"></a>517. Should include name in external representation</h3> -<p><b>Section:</b> 26.5.1 [rand.req], TR1 5.1.1 [tr.rand.req] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2005-07-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.req">issues</a> in [rand.req].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The last two rows of Table 16 deal with the i/o requirements of an engine, -specifying that the textual representation of an engine's state, -appropriately formatted, constitute the engine's external representation. -</p> -<p> -This seems adequate when an engine's type is known. However, it seems -inadequate in the context of generic code, where it becomes useful and -perhaps even necessary to determine an engine's type via input. -</p> -<p> -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -We therefore recommend that, in each of these two rows of Table 16, the -text "textual representation" be expanded so as to read "engine name -followed by the textual representation." -</p> - -<p><i>[ -Berlin: N1932 considers this NAD. This is a QOI issue. -]</i></p> - - - - - - - -<hr> -<h3><a name="526"></a>526. Is it undefined if a function in the standard changes in parameters?</h3> -<p><b>Section:</b> 23.2.3 [sequence.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Chris Jefferson <b>Opened:</b> 2005-09-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#sequence.reqmts">issues</a> in [sequence.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Problem: There are a number of places in the C++ standard library where -it is possible to write what appear to be sensible ways of calling -functions, but which can cause problems in some (or all) -implementations, as they cause the values given to the function to be -changed in a way not specified in standard (and therefore not coded to -correctly work). These fall into two similar categories. -</p> - -<p> -1) Parameters taken by const reference can be changed during execution -of the function -</p> - -<p> -Examples: -</p> - -<p> -Given std::vector<int> v: -</p> -<p> -v.insert(v.begin(), v[2]); -</p> -<p> -v[2] can be changed by moving elements of vector -</p> - - -<p> -Given std::list<int> l: -</p> -<p> -l.remove(*l.begin()); -</p> -<p> -Will delete the first element, and then continue trying to access it. -This is particularily vicious, as it will appear to work in almost all -cases. -</p> - -<p> -2) A range is given which changes during the execution of the function: -Similarly, -</p> - -<p> -v.insert(v.begin(), v.begin()+4, v.begin()+6); -</p> - -<p> -This kind of problem has been partly covered in some cases. For example -std::copy(first, last, result) states that result cannot be in the range -[first, last). However, does this cover the case where result is a -reverse_iterator built from some iterator in the range [first, last)? -Also, std::copy would still break if result was reverse_iterator(last + -1), yet this is not forbidden by the standard -</p> - -<p> -Solution: -</p> - -<p> -One option would be to try to more carefully limit the requirements of -each function. There are many functions which would have to be checked. -However as has been shown in the std::copy case, this may be difficult. -A simpler, more global option would be to somewhere insert text similar to: -</p> - -<p> -If the execution of any function would change either any values passed -by reference or any value in any range passed to a function in a way not -defined in the definition of that function, the result is undefined. -</p> - -<p> -Such code would have to at least cover chapters 23 and 25 (the sections -I read through carefully). I can see no harm on applying it to much of -the rest of the standard. -</p> - -<p> -Some existing parts of the standard could be improved to fit with this, -for example the requires for 25.2.1 (Copy) could be adjusted to: -</p> - -<p> -Requires: For each non-negative integer n < (last - first), assigning to -*(result + n) must not alter any value in the range [first + n, last). -</p> - -<p> -However, this may add excessive complication. -</p> - -<p> -One other benefit of clearly introducing this text is that it would -allow a number of small optimisations, such as caching values passed -by const reference. -</p> - -<p> -Matt Austern adds that this issue also exists for the <tt>insert</tt> and -<tt>erase</tt> members of the ordered and unordered associative containers. -</p> - -<p><i>[ -Berlin: Lots of controversey over how this should be solved. Lots of confusion -as to whether we're talking about self referencing iterators or references. -Needs a good survey as to the cases where this matters, for which -implementations, and how expensive it is to fix each case. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p> -Recommend NAD. -</p> -<ul> -<li><tt>vector::insert(iter, value)</tt> is required to work because the standard -doesn't give permission for it not to work.</li> -<li><tt>list::remove(value)</tt> is required to work because the standard -doesn't give permission for it not to work.</li> -<li><tt>vector::insert(iter, iter, iter)</tt> is not required to work because -23.2.3 [sequence.reqmts], p4 says so.</li> -<li><tt>copy</tt> has to work, except where 25.3.1 [alg.copy] says -it doesn't have to work. While a language lawyer can tear this wording apart, -it is felt that the wording is not prone to accidental interpretation.</li> -<li>The current working draft provide exceptions for the unordered associative -containers similar to the containers requirements which exempt the member -template insert functions from self referencing.</li> -</ul> - - - - - -<hr> -<h3><a name="528"></a>528. <tt>const_iterator</tt> <tt>iterator</tt> issue when they are the same type</h3> -<p><b>Section:</b> 23.5 [unord], TR1 6.3.4 [tr.unord.unord] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Paolo Carlini <b>Opened:</b> 2005-10-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#unord">issues</a> in [unord].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -while implementing the resolution of issue 6.19 I'm noticing the -following: according to 6.3.4.3/2 (and 6.3.4.5/2), for unordered_set and -unordered_multiset: -</p> - -<blockquote><p> - "The iterator and const_iterator types are both const types. It is -unspecified whether they are the same type" -</p></blockquote> - -<p> -Now, according to the resolution of 6.19, we have overloads of insert -with hint and erase (single and range) both for iterator and -const_iterator, which, AFAICS, can be meaningful at the same time *only* -if iterator and const_iterator *are* in fact different types. -</p> -<p> -Then, iterator and const_iterator are *required* to be different types? -Or that is an unintended consequence? Maybe the overloads for plain -iterators should be added only to unordered_map and unordered_multimap? -Or, of course, I'm missing something? -</p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add to 6.3.4.3p2 (and 6.3.4.5p2): -</p> -<p> -2 ... The iterator and const_iterator types are both <del>const</del> -<ins>constant</ins> iterator types. -It is unspecified whether they are the same type. -</p> - -<p> -Add a new subsection to 17.4.4 [lib.conforming]: -</p> - -<blockquote> -<p> -An implementation shall not supply an overloaded function - signature specified in any library clause if such a signature - would be inherently ambiguous during overload resolution - due to two library types referring to the same type. -</p> -<p> - [Note: For example, this occurs when a container's iterator - and const_iterator types are the same. -- end note] -</p> -</blockquote> - -<p><i>[ -Post-Berlin: Beman supplied wording. -]</i></p> - - - - -<p><b>Rationale:</b></p><p> -Toronto: The first issue has been fixed by N2350 (the insert and erase members -are collapsed into one signature). Alisdair to open a separate issue on the -chapter 17 wording. -</p> - - - - -<hr> -<h3><a name="529"></a>529. The standard encourages redundant and confusing preconditions</h3> -<p><b>Section:</b> 17.6.4.11 [res.on.required] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2005-10-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -17.4.3.8/1 says: -</p> - -<blockquote><p> -Violation of the preconditions specified in a function's -Required behavior: paragraph results in undefined behavior unless the -function's Throws: paragraph specifies throwing an exception when the -precondition is violated. -</p></blockquote> - -<p> -This implies that a precondition violation can lead to defined -behavior. That conflicts with the only reasonable definition of -precondition: that a violation leads to undefined behavior. Any other -definition muddies the waters when it comes to analyzing program -correctness, because precondition violations may be routinely done in -correct code (e.g. you can use std::vector::at with the full -expectation that you'll get an exception when your index is out of -range, catch the exception, and continue). Not only is it a bad -example to set, but it encourages needless complication and redundancy -in the standard. For example: -</p> - -<blockquote><pre> - 21 Strings library - 21.3.3 basic_string capacity - - void resize(size_type n, charT c); - - 5 Requires: n <= max_size() - 6 Throws: length_error if n > max_size(). - 7 Effects: Alters the length of the string designated by *this as follows: -</pre></blockquote> - -<p> -The Requires clause is entirely redundant and can be dropped. We -could make that simplifying change (and many others like it) even -without changing 17.4.3.8/1; the wording there just seems to encourage -the redundant and error-prone Requires: clause. -</p> - -<p><i>[ -Batavia: Alan and Pete to work. -]</i></p> - - -<p><i>[ -Bellevue: NAD Editorial, this group likes -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2121.html">N2121</a>, -Pete agrees, accepting it is Pete's business. -General agreement that precondition violations are synonymous with UB. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -1. Change 17.4.3.8/1 to read: -</p> - -<blockquote><p> -Violation of the preconditions specified in a function's -<i>Required behavior:</i> paragraph results in undefined behavior -<del>unless the function's <i>Throws:</i> paragraph specifies throwing -an exception when the precondition is violated</del>. -</p></blockquote> - -<p> -2. Go through and remove redundant Requires: clauses. Specifics to be - provided by Dave A. -</p> - -<p><i>[ -Berlin: The LWG requests a detailed survey of part 2 of the proposed resolution. -]</i></p> - - -<p><i>[ -Alan provided the survey -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2121.html">N2121</a>. -]</i></p> - - - - - - - -<hr> -<h3><a name="536"></a>536. Container iterator constructor and explicit convertibility</h3> -<p><b>Section:</b> 23.2 [container.requirements] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Joaquín M López Muñoz <b>Opened:</b> 2005-12-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#container.requirements">active issues</a> in [container.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#container.requirements">issues</a> in [container.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#589">589</a></p> -<p><b>Discussion:</b></p> -<p> -The iterator constructor X(i,j) for containers as defined in 23.1.1 and -23.2.2 does only require that i and j be input iterators but -nothing is said about their associated value_type. There are three -sensible -options: -</p> -<ol> -<li>iterator's value_type is exactly X::value_type (modulo cv).</li> -<li>iterator's value_type is *implicitly* convertible to X::value_type.</li> -<li>iterator's value_type is *explicitly* convertible to X::value_type.</li> -</ol> -<p> -The issue has practical implications, and stdlib vendors have -taken divergent approaches to it: Dinkumware follows 2, -libstdc++ follows 3. -</p> -<p> -The same problem applies to the definition of insert(p,i,j) for -sequences and insert(i,j) for associative contianers, as well as -assign. -</p> - -<p><i>[ -The following added by Howard and the example code was originally written by -Dietmar. -]</i></p> - -<p> -Valid code below? -</p> - -<blockquote><pre> -#include <vector> -#include <iterator> -#include <iostream> - -struct foo -{ - explicit foo(int) {} -}; - -int main() -{ - std::vector<int> v_int; - std::vector<foo> v_foo1(v_int.begin(), v_int.end()); - std::vector<foo> v_foo2((std::istream_iterator<int>(std::cin)), - std::istream_iterator<int>()); -} -</pre></blockquote> -<p><i>[ -Berlin: Some support, not universal, for respecting the explicit qualifier. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> - - - - - - -<hr> -<h3><a name="544"></a>544. minor NULL problems in C.2</h3> -<p><b>Section:</b> C.5 [diff.library] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2005-11-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#diff.library">issues</a> in [diff.library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -According to C.2.2.3, p1, "the macro NULL, defined in any of <clocale>, -<cstddef>, <cstdio>, <cstdlib>, <cstring>, <ctime>, -or <cwchar>." This is consistent with the C standard. -</p> -<p> -However, Table 95 in C.2 fails to mention <clocale> and <cstdlib>. -</p> -<p> -In addition, C.2, p2 claims that "The C++ Standard library provides -54 standard macros from the C library, as shown in Table 95." While -table 95 does have 54 entries, since a couple of them (including the -NULL macro) are listed more than once, the actual number of macros -defined by the C++ Standard Library may not be 54. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -I propose we add <clocale> and <cstdlib> to Table 96 and remove the -number of macros from C.2, p2 and reword the sentence as follows: -</p> -<blockquote><p> -The C++ Standard library <del>provides 54 standard macros from</del> -<ins>defines a number macros corresponding to those defined by</ins> the C -<ins>Standard</ins> library, as shown in Table 96. -</p></blockquote> - -<p><i>[ -Portland: Resolution is considered editorial. It will be incorporated into the WD. -]</i></p> - - - - - - - -<hr> -<h3><a name="546"></a>546. _Longlong and _ULonglong are integer types</h3> -<p><b>Section:</b> TR1 5.1.1 [tr.rand.req] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2006-01-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The TR sneaks in two new integer types, _Longlong and _Ulonglong, in [tr.c99]. -The rest of the TR should use that type. I believe this affects two places. -First, the random number requirements, 5.1.1/10-11, lists all of the types with -which template parameters named IntType and UIntType may be instantiated. -_Longlong (or "long long", assuming it is added to C++0x) should be added to the -IntType list, and UIntType (again, or "unsigned long long") should be added to -the UIntType list. Second, 6.3.2 lists the types for which hash<> is -required to be instantiable. _Longlong and _Ulonglong should be added to that -list, so that people may use long long as a hash key. -</p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -We are not going to fix TR1. -</p> -<p> -The paper "long long goes to the library" addresses the integration of -long long into the C++0x library. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="547"></a>547. division should be floating-point, not integer</h3> -<p><b>Section:</b> 26.5 [rand], TR1 5.1 [tr.rand] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2006-01-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand">issues</a> in [rand].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Paragraph 10 describes how a variate generator uses numbers produced by an -engine to pass to a generator. The sentence that concerns me is: "Otherwise, if -the value for engine_value_type::result_type is true and the value for -Distribution::input_type is false [i.e. if the engine produces integers and the -engine wants floating-point values], then the numbers in s_eng are divided by -engine().max() - engine().min() + 1 to obtain the numbers in s_e." Since the -engine is producing integers, both the numerator and the denominator are -integers and we'll be doing integer division, which I don't think is what we -want. Shouldn't we be performing a conversion to a floating-point type first? -</p> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p> -Recommend NAD as the affected section is now gone and so the issue is moot. -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2111.pdf">N2111</a>. -</p> - - - - - -<hr> -<h3><a name="548"></a>548. May random_device block?</h3> -<p><b>Section:</b> 26.5.6 [rand.device], TR1 5.1.6 [tr.rand.device] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2006-01-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.device">issues</a> in [rand.device].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Class random_device "produces non-deterministic random numbers", using some -external source of entropy. In most real-world systems, the amount of available -entropy is limited. Suppose that entropy has been exhausted. What is an -implementation permitted to do? In particular, is it permitted to block -indefinitely until more random bits are available, or is the implementation -required to detect failure immediately? This is not an academic question. On -Linux a straightforward implementation would read from /dev/random, and "When -the entropy pool is empty, reads to /dev/random will block until additional -environmental noise is gathered." Programmers need to know whether random_device -is permitted to (or possibly even required to?) behave the same way. -</p> - -<p><i>[ -Berlin: Walter: N1932 considers this NAD. Does the standard specify whether std::cin -may block? -]</i></p> - - -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2391.pdf">N2391</a> and -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2423.pdf">N2423</a> -for some further discussion. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Adopt the proposed resolution in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2423.pdf">N2423</a> (NAD). -</p> - - - - - -<hr> -<h3><a name="549"></a>549. Undefined variable in binomial_distribution</h3> -<p><b>Section:</b> 26.5.8 [rand.dist], TR1 5.1.7.5 [tr.rand.dist.bin] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2006-01-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.dist">issues</a> in [rand.dist].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Paragraph 1 says that "A binomial distributon random distribution produces -integer values i>0 with p(i) = (n choose i) * p*i * (1-p)^(t-i), where t and -p are the parameters of the distribution. OK, that tells us what t, p, and i -are. What's n? -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Berlin: Typo: "n" replaced by "t" in N1932: see 26.3.7.2.2/1. -</p> - -<p><i>[ -Portland: Subsumed by N2111. -]</i></p> - - - - - - -<hr> -<h3><a name="553"></a>553. very minor editorial change <tt>intptr_t</tt> / <tt>uintptr_t</tt></h3> -<p><b>Section:</b> 18.4.1 [cstdint.syn], TR1 8.22.1 [tr.c99.cstdint.syn] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Paolo Carlini <b>Opened:</b> 2006-01-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#cstdint.syn">issues</a> in [cstdint.syn].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In the synopsis, some types are identified as optional: <tt>int8_t</tt>, <tt>int16_t</tt>, -and so on, consistently with C99, indeed. -</p> -<p> -On the other hand, <tt>intptr_t</tt> and <tt>uintptr_t</tt>, are not marked as such and -probably should, consistently with C99, 7.18.1.4. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 18.4.1 [cstdint.syn]: -</p> - -<blockquote><pre> -... -typedef <i>signed integer type</i> intptr_t; <ins><i>// optional</i></ins> -... -typedef <i>unsigned integer type</i> uintptr_t; <ins><i>// optional</i></ins> -... -</pre></blockquote> - - - -<p><b>Rationale:</b></p><p> -Recommend NAD and fix as editorial with the proposed resolution. -</p> - - - - -<hr> -<h3><a name="554"></a>554. Problem with lwg DR 184 numeric_limits<bool></h3> -<p><b>Section:</b> 18.3.2.7 [numeric.special] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2006-01-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#numeric.special">issues</a> in [numeric.special].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I believe we have a bug in the resolution of: -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#184">lwg 184</a> -(WP status). -</p> - -<p> -The resolution spells out each member of <tt>numeric_limits<bool></tt>. -The part I'm having a little trouble with is: -</p> -<blockquote><pre> -static const bool traps = false; -</pre></blockquote> - -<p> -Should this not be implementation defined? Given: -</p> - -<blockquote><pre> -int main() -{ - bool b1 = true; - bool b2 = false; - bool b3 = b1/b2; -} -</pre></blockquote> - -<p> -If this causes a trap, shouldn't <tt>numeric_limits<bool>::traps</tt> be -<tt>true</tt>? -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 18.2.1.5p3: -</p> - -<blockquote><p> --3- The specialization for <tt>bool</tt> shall be provided as follows: </p> -<blockquote><pre> -namespace std { - template <> class numeric_limits<bool> { - ... - static const bool traps = <del>false</del> <ins><i>implementation-defined</i></ins>; - ... - }; -} -</pre></blockquote> -</blockquote> - -<p><i>[ -Redmond: NAD because traps refers to values, not operations. There is no bool -value that will trap. -]</i></p> - - - - - - - -<hr> -<h3><a name="555"></a>555. TR1, 8.21/1: typo</h3> -<p><b>Section:</b> TR1 8.21 [tr.c99.boolh] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Paolo Carlini <b>Opened:</b> 2006-02-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -This one, if nobody noticed it yet, seems really editorial: -s/cstbool/cstdbool/ -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 8.21p1: -</p> -<blockquote><p> --1- The header behaves as if it defines the additional macro defined in -<tt><cst<ins>d</ins>bool></tt> by including the header <tt><cstdbool></tt>. -</p></blockquote> - -<p><i>[ -Redmond: Editorial. -]</i></p> - - - - - - - -<hr> -<h3><a name="557"></a>557. TR1: div(_Longlong, _Longlong) vs div(intmax_t, intmax_t)</h3> -<p><b>Section:</b> 18.4 [cstdint], TR1 8.22 [tr.c99.cstdint] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Paolo Carlini <b>Opened:</b> 2006-02-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#cstdint">issues</a> in [cstdint].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I'm seeing a problem with such overloads: when, _Longlong == intmax_t == -long long we end up, essentially, with the same arguments and different -return types (lldiv_t and imaxdiv_t, respectively). Similar issue with -abs(_Longlong) and abs(intmax_t), of course. -</p> -<p> -Comparing sections 8.25 and 8.11, I see an important difference, -however: 8.25.3 and 8.25.4 carefully describe div and abs for _Longlong -types (rightfully, because not moved over directly from C99), whereas -there is no equivalent in 8.11: the abs and div overloads for intmax_t -types appear only in the synopsis and are not described anywhere, in -particular no mention in 8.11.2 (at variance with 8.25.2). -</p> -<p> -I'm wondering whether we really, really, want div and abs for intmax_t... -</p> - - - -<p><b>Proposed resolution:</b></p> - - - -<p><i>[ -Portland: no consensus. -]</i></p> - - -<p><b>Rationale:</b></p> -<p><i>[ -Batavia, Bill: The <tt><cstdint></tt> synopsis in TR1 8.11.1 [tr.c99.cinttypes.syn] contains: -]</i></p> - -<blockquote><pre> -intmax_t imaxabs(intmax_t i); -intmax_t abs(intmax_t i); - -imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom); -imaxdiv_t div(intmax_t numer, intmax_t denom); -</pre></blockquote> - -<p><i>[ -and in TR1 8.11.2 [tr.c99.cinttypes.def]: -]</i></p> - - -<blockquote><p> -The header defines all functions, types, and macros the same as C99 -subclause 7.8. -</p></blockquote> - -<p><i>[ -This is as much definition as we give for most other C99 functions, -so nothing need change. We might, however, choose to add the footnote: -]</i></p> - - -<blockquote><p> -[<i>Note:</i> These overloads for <tt>abs</tt> and <tt>div</tt> may well be equivalent to -those that take <tt>long long</tt> arguments. If so, the implementation is -responsible for avoiding conflicting declarations. -- <i>end note</i>] -</p></blockquote> - -<p><i>[ -Bellevue: NAD Editorial. Pete must add a footnote, as described below. -]</i></p> - - -<blockquote> -<p><i>[ -Looks like a real problem. Dietmar suggests div() return a template -type. Matt: looks like imaxdiv_t is loosly defined. Can it be a typedef -for lldiv_t when _Longlong == intmax_t? PJP seems to agree. We would -need a non-normative note declaring that the types lldiv_t and imaxdiv_t -may not be unique if intmax_t==_longlong. -]</i></p> - -</blockquote> - - - - - - -<hr> -<h3><a name="558"></a>558. lib.input.iterators Defect</h3> -<p><b>Section:</b> 24.2.3 [input.iterators] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2006-02-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#input.iterators">issues</a> in [input.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<blockquote> -<p> - 24.1.1 Input iterators [lib.input.iterators] -</p> -<p> - 1 A class or a built-in type X satisfies the requirements of an - input iterator for the value type T if the following expressions are - valid, where U is the type of any specified member of type T, as - shown in Table 73. -</p> -</blockquote> -<p> -There is no capital U used in table 73. There is a lowercase u, but -that is clearly not meant to denote a member of type T. Also, there's -no description in 24.1.1 of what lowercase a means. IMO the above -should have been...Hah, a and b are already covered in 24.1/11, so maybe it -should have just been: -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 24.1.1p1: -</p> -<blockquote><p> --1- A class or a built-in type <tt>X</tt> satisfies the requirements of an -input iterator for the value type <tt>T</tt> if the following expressions -are valid<del>, where <tt>U</tt> is the type of any specified member of type -<tt>T</tt>,</del> as shown in Table 73. -</p></blockquote> - -<p><i>[ -Portland: Editorial. -]</i></p> - - - - - - - -<hr> -<h3><a name="560"></a>560. User-defined allocators without default constructor</h3> -<p><b>Section:</b> 17.6.3.5 [allocator.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Sergey P. Derevyago <b>Opened:</b> 2006-02-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#allocator.requirements">active issues</a> in [allocator.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#allocator.requirements">issues</a> in [allocator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<h4>1. The essence of the problem.</h4> -<p> -User-defined allocators without default constructor are not explicitly -supported by the standard but they can be supported just like std::vector -supports elements without default constructor. -</p> -<p> -As a result, there exist implementations that work well with such allocators -and implementations that don't. -</p> - -<h4>2. The cause of the problem.</h4> -<p> -1) The standard doesn't explicitly state this intent but it should. In -particular, 20.1.5p5 explicitly state the intent w.r.t. the allocator -instances that compare non-equal. So it can similarly state the intent w.r.t. -the user-defined allocators without default constructor. -</p> -<p> -2) Some container operations are obviously underspecified. In particular, -21.3.7.1p2 tells: -</p> -<blockquote><pre> -template<class charT, class traits, class Allocator> - basic_string<charT,traits,Allocator> operator+( - const charT* lhs, - const basic_string<charT,traits,Allocator>& rhs - ); -</pre> -<p> -Returns: <tt>basic_string<charT,traits,Allocator>(lhs) + rhs</tt>. -</p> -</blockquote> -<p> -That leads to the basic_string<charT,traits,Allocator>(lhs, Allocator()) call. -Obviously, the right requirement is: -</p> -<blockquote><p> -Returns: <tt>basic_string<charT,traits,Allocator>(lhs, rhs.get_allocator()) + rhs</tt>. -</p></blockquote> -<p> -It seems like a lot of DRs can be submitted on this "Absent call to -get_allocator()" topic. -</p> - -<h4>3. Proposed actions.</h4> -<p> -1) Explicitly state the intent to allow for user-defined allocators without -default constructor in 20.1.5 Allocator requirements. -</p> -<p> -2) Correct all the places, where a correct allocator object is available -through the get_allocator() call but default Allocator() gets passed instead. -</p> -<h4>4. Code sample.</h4> -<p> -Let's suppose that the following memory pool is available: -</p> -<blockquote><pre> -class mem_pool { - // ... - void* allocate(size_t size); - void deallocate(void* ptr, size_t size); -}; -</pre></blockquote> -<p> -So the following allocator can be implemented via this pool: -</p> -<blockquote><pre> -class stl_allocator { - mem_pool& pool; - - public: - explicit stl_allocator(mem_pool& mp) : pool(mp) {} - stl_allocator(const stl_allocator& sa) : pool(sa.pool) {} - template <class U> - stl_allocator(const stl_allocator<U>& sa) : pool(sa.get_pool()) {} - ~stl_allocator() {} - - pointer allocate(size_type n, std::allocator<void>::const_pointer = 0) - { - return (n!=0) ? static_cast<pointer>(pool.allocate(n*sizeof(T))) : 0; - } - - void deallocate(pointer p, size_type n) - { - if (n!=0) pool.deallocate(p, n*sizeof(T)); - } - - // ... -}; -</pre></blockquote> -<p> -Then the following code works well on some implementations and doesn't work on -another: -</p> -<blockquote><pre> -typedef basic_string<char, char_traits<char>, stl_allocator<char> > - tl_string; -mem_pool mp; -tl_string s1("abc", stl_allocator<int>(mp)); -printf("(%s)\n", ("def"+s1).c_str()); -</pre></blockquote> -<p> -In particular, on some implementations the code can't be compiled without -default stl_allocator() constructor. -</p> -<p> -The obvious way to solve the compile-time problems is to intentionally define -a NULL pointer dereferencing default constructor -</p> -<blockquote><pre> -stl_allocator() : pool(*static_cast<mem_pool*>(0)) {} -</pre></blockquote> -<p> -in a hope that it will not be called. The problem is that it really gets -called by operator+(const char*, const string&) under the current 21.3.7.1p2 -wording. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p> -<p> -Recommend NAD. <tt>operator+()</tt> with <tt>string</tt> already requires the desired -semantics of copying the allocator from one of the strings (<i>lhs</i> when there is a choice). -</p> - - - - - -<hr> -<h3><a name="568"></a>568. <tt>log2</tt> overloads missing</h3> -<p><b>Section:</b> TR1 8.16.4 [tr.c99.cmath.over] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Paolo Carlini <b>Opened:</b> 2006-03-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -<tt>log2</tt> is missing from the list of "additional overloads" in TR1 8.16.4 [tr.c99.cmath.over] p1. -</p> - -<p> -Hinnant: This is a TR1 issue only. It is fixed in the current (N2135) WD. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree this has been fixed in the Working Draft. -Move to NAD. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Add <tt>log2</tt> to the list of functions in TR1 8.16.4 [tr.c99.cmath.over] p1. -</p> - - - - - -<hr> -<h3><a name="569"></a>569. Postcondition for basic_ios::clear(iostate) incorrectly stated</h3> -<p><b>Section:</b> 27.5.5.4 [iostate.flags] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Seungbeom Kim <b>Opened:</b> 2006-03-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iostate.flags">issues</a> in [iostate.flags].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#272">272</a></p> -<p><b>Discussion:</b></p> -<p> -Section: 27.4.4.3 [lib.iostate.flags] -</p> -<p> -Paragraph 4 says: -</p> -<blockquote> -<blockquote><pre> -void clear(iostate <i>state</i> = goodbit); -</pre></blockquote> -<p> -<i>Postcondition:</i> If <tt>rdbuf()!=0</tt> then <tt><i>state</i> == rdstate();</tt> -otherwise <tt>rdstate()==<i>state</i>|ios_base::badbit</tt>. -</p> -</blockquote> - -<p> -The postcondition "rdstate()==state|ios_base::badbit" is parsed as -"(rdstate()==state)|ios_base::badbit", which is probably what the -committee meant. -</p> - - - - -<p><b>Rationale:</b></p> - - - - - - -<hr> -<h3><a name="570"></a>570. Request adding additional explicit specializations of <tt>char_traits</tt></h3> -<p><b>Section:</b> 21.2 [char.traits] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Jack Reeves <b>Opened:</b> 2006-04-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#char.traits">issues</a> in [char.traits].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Currently, the Standard Library specifies only a declaration for template class -<tt>char_traits<></tt> and requires the implementation provide two explicit -specializations: <tt>char_traits<char></tt> and <tt>char_traits<wchar_t></tt>. -I feel the Standard should require explicit specializations for all built-in -character types, i.e. <tt>char</tt>, <tt>wchar_t</tt>, <tt>unsigned char</tt>, -and <tt>signed char</tt>. -</p> -<p> -I have put together a paper -(<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1985.htm">N1985</a>) -that describes this in more detail and -includes all the necessary wording. -</p> -<p><i>[ -Portland: Jack will rewrite -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n1985.htm">N1985</a> -to propose a primary template that will work with other integral types. -]</i></p> - -<p><i>[ -Toronto: issue has grown with addition of <tt>char16_t</tt> and <tt>char32_t</tt>. -]</i></p> - - -<p><i>[ -post Bellevue: -]</i></p> - - -<blockquote> -<p> -We suggest that Jack be asked about the status of his paper, and if it -is not forthcoming, the work-item be assigned to someone else. If no one -steps forward to do the paper before the next meeting, we propose to -make this NAD without further discussion. We leave this Open for now, -but our recommendation is NAD. -</p> -<p> -Note: the issue statement should be updated, as the Toronto comment has -already been resolved. E.g., char_traits specializations for <tt>char16_t</tt> -and <tt>char32_t</tt> are now in the working paper. -</p> -</blockquote> - -<p><i>[ -Sophia Antipolis: -]</i></p> - - -<blockquote><p> -Nobody has submitted the requested paper, so we move to NAD, as suggested by the decision at the last meeting. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="571"></a>571. Update C90 references to C99?</h3> -<p><b>Section:</b> 1.2 [intro.refs] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2006-04-08 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#intro.refs">issues</a> in [intro.refs].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -1.2 Normative references [intro.refs] of the WP currently refers to ISO/IEC -9899:1990, Programming languages - C. Should that be changed to ISO/IEC -9899:1999? -</p> -<p> -What impact does this have on the library? -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In 1.2/1 [intro.refs] of the WP, change: -</p> -<blockquote> -<ul> -<li>ISO/IEC 9899:<del>1990</del><ins>1999 + TC1 + TC2</ins>, <i>Programming languages - C</i></li> -</ul> -</blockquote> - - - -<p><b>Rationale:</b></p><p> -Recommend NAD, fixed editorially. -</p> - - - - -<hr> -<h3><a name="572"></a>572. Oops, we gave 507 WP status</h3> -<p><b>Section:</b> 26.5 [rand], TR1 5.1 [tr.rand] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2006-04-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand">issues</a> in [rand].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In Berlin, as a working group, we voted in favor of N1932 which makes issue 507 moot: -variate_generator has been eliminated. Then in full committee we voted to give -this issue WP status (mistakenly). -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Strike the proposed resolution of issue 507. -</p> -<p><i>[ -post-Portland: Walter and Howard recommend NAD. The proposed resolution of 507 no longer -exists in the current WD. -]</i></p> - - - -<p><b>Rationale:</b></p> -<p> -NAD. Will be moot once -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2135.pdf">N2135</a> -is adopted. -</p> - - - - - -<hr> -<h3><a name="573"></a>573. C++0x file positioning should handle modern file sizes</h3> -<p><b>Section:</b> 27.5.4 [fpos] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2006-04-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#fpos">issues</a> in [fpos].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -There are two deficiencies related to file sizes: -</p> -<ol> -<li>It doesn't appear that the Standard Library is specified in - a way that handles modern file sizes, which are often too - large to be represented by an unsigned long.</li> - -<li>The <tt>std::fpos</tt> class does not currently have the ability to - set/get file positions.</li> -</ol> -<p> -The Dinkumware implementation of the Standard Library as shipped with the Microsoft compiler copes with these issues by: -</p> -<ol style="list-style-type:upper-alpha"> -<li>Defining <tt>fpos_t</tt> be <tt>long long</tt>, which is large enough to - represent any file position likely in the foreseeable future.</li> - -<li>Adding member functions to class <tt>fpos</tt>. For example, -<blockquote><pre> -fpos_t seekpos() const; -</pre></blockquote> -</li> -</ol> -<p> -Because there are so many types relating to file positions and offsets (<tt>fpos_t</tt>, -<tt>fpos</tt>, <tt>pos_type</tt>, <tt>off_type</tt>, <tt>streamoff</tt>, <tt>streamsize</tt>, -<tt>streampos</tt>, <tt>wstreampos</tt>, and perhaps more), it is difficult to know if -the Dinkumware extensions are sufficient. But they seem a useful starting place for -discussions, and they do represent existing practice. -</p> - -<p><i>[ -Kona (2007): We need a paper. It would be nice if someone proposed -clarifications to the definitions of <tt>pos_type</tt> and <tt>off_type</tt>. Currently -these definitions are horrible. Proposed Disposition: Open -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -This is the subject of paper N2926. -</p> -<p> -If we choose to take any action, we will move the paper, so the issue can be closed. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="579"></a>579. <tt>erase(iterator)</tt> for unordered containers should not return an iterator</h3> -<p><b>Section:</b> 23.2.5 [unord.req] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Joaquín M López Muñoz <b>Opened:</b> 2006-06-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#unord.req">active issues</a> in [unord.req].</p> -<p><b>View all other</b> <a href="lwg-index.html#unord.req">issues</a> in [unord.req].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses ES-2</b></p> - -<p> -See -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2023.pdf">N2023</a> -for full discussion. -</p> - -<p><i>[ -2009-12-11 Paolo opens: -]</i></p> - - -<blockquote><p> -I'm asking for DR 579 to be re-opened, basing on recent discussions on the -library reflector, see Message c++std-lib-26040 and replies. -</p></blockquote> - -<p><i>[ -2010-02-07 Paolo updates wording. -]</i></p> - - -<blockquote><p> -As pointed out by Chris in c++std-lib-26040, that an -<tt>erase(unordered_container, iterator)</tt> returning an <tt>iterator</tt> can -easily implemented in user code, if needed; that actually returning an -<tt>iterator</tt> costs nothing for the overload taking two <tt>iterator</tt>s, -thus that proposed change is only for consistency; that -<tt>forward_list::erase_after</tt> also returns <tt>void</tt> (for different -reasons, granted, but isn't that any "<tt>erase</tt>" function in the containers -uniformly returns an <tt>iterator</tt>); that, also in thread started by Chris' -message, Alberto pointed out that the proxy idea isn't a good one; that users -both of the GNU and Boost implementations are reporting serious performance -problems with the current version returning an <tt>iterator</tt>. -</p></blockquote> - -<p><i>[ -2010-02-07 Original wording saved here: -]</i></p> - - -<blockquote class="note"> -<p> -Option 1: -</p> - -<p> -The problem can be eliminated by omitting the requirement that <tt>a.erase(q)</tt> return an -iterator. This is, however, in contrast with the equivalent requirements for other -standard containers. -</p> - -<p> -Option 2: -</p> - -<p> -<tt>a.erase(q)</tt> can be made to compute the next iterator only when explicitly requested: -the technique consists in returning a proxy object implicitly convertible to <tt>iterator</tt>, so -that -</p> - -<blockquote><pre> -iterator q1=a.erase(q); -</pre></blockquote> - -<p> -works as expected, while -</p> - -<blockquote><pre> -a.erase(q); -</pre></blockquote> - -<p> -does not ever invoke the conversion-to-iterator operator, thus avoiding the associated -computation. To allow this technique, some sections of TR1 along the line "return value -is an iterator..." should be changed to "return value is an unspecified object implicitly -convertible to an iterator..." Although this trick is expected to work transparently, it can -have some collateral effects when the expression <tt>a.erase(q)</tt> is used inside generic -code. -</p> - -</blockquote> - -<p><i>[ -2010-03-27 Joaquín adds: -]</i></p> - - -<blockquote> -<p> -Signature of <tt>iterator erase(const_iterator)</tt> should be changed to <tt>void -erase(const_iterator)</tt>. If this is not viable an acceptable tradeoff -could be to make the return type of <tt>erase(const_iterator)</tt> -<i>implementation defined</i>. -</p> - -<p> -The standard should allow implementations of unordered associative -containers using either singly or doubly linked lists. -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2023.pdf">N2023</a> -proves that singly-linked lists implementations cannot provide the required -complexity for <tt>iterator erase(const_iterator)</tt>. Thus, some action is -needed to allow both implementations. -</p> - -<p> -Option 1: Changing the required complexity from O(1) to O(log n). This option -merely masks a design flaw. Users are forcefully penalized for what they don't -use (the returned iterator). Besides, they would have to learn about the -pathological (yet very real) situations where using <tt>erase</tt> can lead to -quadratic performance. Two out of these three objections remain even if some -alternative member function like <tt>void quick_erase(const_iterator)</tt> is -thrown in to the interface. -</p> - -<p> -Some objections have been expressed to changing return type of <tt>erase</tt> to -<tt>void</tt>, arguing that it would break current existing practice with -standard library implementations based on doubly-linked lists, where the problem -does not occur. However implementations based on drafts should not block the -resolution of a serious design issue, more so when the issue will hurt future -users of C++, as it's happening already. -</p> - -<p> -Option 2: Make <tt>erase</tt> return type <i>implementation defined</i>. There's -a possible tradeoff with the objectors above consisting in changing the -signature to <i>implementation defined</i> <tt>erase(iterator)</tt>, so that -returning an iterator is indeed a valid extension. To this it can be argued that -this would make implementantions returning an iterator look as somehow promoting -proprietary extensions: this in my opinion is not a valid argument since those -implementations are <em>already</em> extending the required interface by -providing bidirectional iterators (just forward iterators are required). -</p> -</blockquote> - -<p><i>[ -2010 Rapperswil: -]</i></p> - - -<blockquote> -<p> -The issue was lengthy discussed and implementation experience was demonstrated that a non-void return -type is implementable for both single-linked and double-linked lists without loss of efficiency. -</p> - -<p> -By a 12-1-1-0 poll voted to keep the return type of erase as <tt>iterator</tt> instead of -<tt>void</tt> and a second 0-0-3-10 poll rejected the additional proposal to add a -<tt>quick_erase</tt> returning <tt>void</tt>, thus LWG decided for NAD. -</p> -</blockquote> - - -<p><b>Rationale:</b></p> - -<p> -No consensus for a change. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="580"></a>580. unused allocator members</h3> -<p><b>Section:</b> 23.2.1 [container.requirements.general] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2006-06-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#container.requirements.general">active issues</a> in [container.requirements.general].</p> -<p><b>View all other</b> <a href="lwg-index.html#container.requirements.general">issues</a> in [container.requirements.general].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-closed.html#479">479</a></p> -<p><b>Discussion:</b></p> -<p> - -C++ Standard Library templates that take an allocator as an argument -are required to call the <code>allocate()</code> and -<code>deallocate()</code> members of the allocator object to obtain -storage. However, they do not appear to be required to call any other -allocator members such as <code>construct()</code>, -<code>destroy()</code>, <code>address()</code>, and -<code>max_size()</code>. This makes these allocator members less than -useful in portable programs. - - </p> - <p> - -It's unclear to me whether the absence of the requirement to use these -allocator members is an unintentional omission or a deliberate -choice. However, since the functions exist in the standard allocator -and since they are required to be provided by any user-defined -allocator I believe the standard ought to be clarified to explictly -specify whether programs should or should not be able to rely on -standard containers calling the functions. - - </p> - <p> - -I propose that all containers be required to make use of these -functions. - - </p> -<p><i>[ -Batavia: We support this resolution. Martin to provide wording. -]</i></p> - -<p><i>[ -pre-Oxford: Martin provided wording. -]</i></p> - - -<p><i>[ -2009-04-28 Pablo adds: -]</i></p> - - -<blockquote><p> -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2554.pdf">N2554</a> -(scoped allocators), -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2768.pdf">N2768</a> -(allocator concepts), and -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2810.pdf">N2810</a> -(allocator defects), address all of these points EXCEPT <tt>max_size()</tt>. -So, I would add a note to that affect and re-class the defect as belonging -to section 23.2.1 [container.requirements.general]. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -The comment in the description of this issue that this "would be" -rendered editorial by the adoption of N2257 is confusing. It appears -that N2257 was never adopted. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -NAD Editorial. Addressed by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2982.pdf">N2982</a>. -</p></blockquote> - - - - <p><b>Proposed resolution:</b></p> - <p> - -Specifically, I propose to change 23.2 [container.requirements], -p9 as follows: - - </p> - <blockquote> -<p> --9- Copy constructors for all container types defined in this clause -<ins>that are parametrized on <code>Allocator</code></ins> copy -<del>an</del><ins>the</ins> allocator argument from their respective -first parameters. - -All other constructors for these container types take a<del>n</del> -<ins>const</ins> <code>Allocator&</code> argument (20.1.6), an -allocator whose <code>value_type</code> is the same as the container's -<code>value_type</code>. - -A copy of this argument <del>is</del><ins>shall be</ins> used for any -memory allocation <ins> and deallocation</ins> performed<del>,</del> -by these constructors and by all member functions<del>,</del> during -the lifetime of each container object. <ins>Allocation shall be -performed "as if" by calling the <code>allocate()</code> member -function on a copy of the allocator object of the appropriate type -<sup>New Footnote)</sup>, and deallocation "as if" by calling -<code>deallocate()</code> on a copy of the same allocator object of -the corresponding type.</ins> - -<ins>A copy of this argument shall also be used to construct and -destroy objects whose lifetime is managed by the container, including -but not limited to those of the container's <code>value_type</code>, -and to obtain their address. All objects residing in storage -allocated by a container's allocator shall be constructed "as if" by -calling the <code>construct()</code> member function on a copy of the -allocator object of the appropriate type. The same objects shall be -destroyed "as if" by calling <code>destroy()</code> on a copy of the -same allocator object of the same type. The address of such objects -shall be obtained "as if" by calling the <code>address()</code> member -function on a copy of the allocator object of the appropriate -type.</ins> - -<ins>Finally, a copy of this argument shall be used by its container -object to determine the maximum number of objects of the container's -<code>value_type</code> the container may store at the same time. The -container member function <code>max_size()</code> obtains this number -from the value returned by a call to -<code>get_allocator().max_size()</code>.</ins> - -In all container types defined in this clause <ins>that are -parametrized on <code>Allocator</code></ins>, the member -<code>get_allocator()</code> returns a copy of the -<code>Allocator</code> object used to construct the -container.<sup>258)</sup> -</p> -<p> -New Footnote: This type may be different from <code>Allocator</code>: -it may be derived from <code>Allocator</code> via -<code>Allocator::rebind<U>::other</code> for the appropriate -type <code>U</code>. -</p> - </blockquote> - <p> - -The proposed wording seems cumbersome but I couldn't think of a better -way to describe the requirement that containers use their -<code>Allocator</code> to manage only objects (regardless of their -type) that persist over their lifetimes and not, for example, -temporaries created on the stack. That is, containers shouldn't be -required to call <code>Allocator::construct(Allocator::allocate(1), -elem)</code> just to construct a temporary copy of an element, or -<code>Allocator::destroy(Allocator::address(temp), 1)</code> to -destroy temporaries. - - </p> - - -<p><i>[ -Howard: This same paragraph will need some work to accommodate <a href="lwg-defects.html#431">431</a>. -]</i></p> - - -<p><i>[ -post Oxford: This would be rendered NAD Editorial by acceptance of -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2257.html">N2257</a>. -]</i></p> - - - - - -<hr> -<h3><a name="582"></a>582. specialized algorithms and volatile storage</h3> -<p><b>Section:</b> 20.7.12.2 [uninitialized.copy] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2006-06-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#uninitialized.copy">issues</a> in [uninitialized.copy].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p>Related to <a href="lwg-closed.html#1029">1029</a></p> - <p> - -The specialized algorithms [lib.specialized.algorithms] are specified -as having the general effect of invoking the following expression: - - </p> - <pre> - -new (static_cast<void*>(&*i)) - typename iterator_traits<ForwardIterator>::value_type (x) - - </pre> - <p> - -This expression is ill-formed when the type of the subexpression -<code>&*i</code> is some volatile-qualified <code>T</code>. - - </p> - -<p><i>[ -Batavia: Lack of support for proposed resolution but agree there is a -defect. Howard to look at wording. Concern that move semantics -properly expressed if iterator returns rvalue. -]</i></p> - - - -<p><i>[ -2009-06-17 Pablo adds: -]</i></p> - - -<blockquote> - -<p>Propose that Issue <a href="lwg-closed.html#582">582</a> be closed NAD.</p> -<p> -Issue <a href="lwg-closed.html#582">582</a> asks that <tt>uninitialized_copy</tt>, -<tt>uninitialized_fill</tt>, and <tt>uninitialized_fill_n</tt> should be -well-formed if the result type is volatile. My feeling is that the -standard does not, and should not, guarantee any useful behavior when -constructors are invoked on volatile storage, so making it syntactically -legal to call <tt>uninitialized_copy</tt> on volatile storage is not useful. A -possible editorial change would be to put my previous sentence into a -non-normative note. -</p> -<p> -Note that the three sections starting with 20.7.12.2 [uninitialized.copy] do not -yet have concepts. Here's a first crack at the first one: -</p> -<blockquote><pre> -template <InputIterator InIter, OutputIterator OutIter> -requires ExplicitConvertible<HasDereference<OutIter::reference>::result, - OutIter::value_type&> - && Convertible<OutIter::value_type*, void*> - && ExplicitConvertible<OutIter::value_type, InIter::reference> - OutIter uninitialized_copy(InIter first, InIter last, OutIter result); -</pre> -<blockquote> -<p> -Effects: -</p> -<blockquote><pre> -while (first != last) { - typedef OutIter::value_type value_type; - value_type& outRef = static_cast<value_type&>(*result++); - ::new (static_cast<void*>(addressof(outRef))) value_type(*first++); -} -</pre></blockquote> -</blockquote> - -</blockquote> - -<p> -Notes: -</p> -<ol> -<li>This definition is actually LESS constrained than in C++03 because -there is no requirement that the result be a forward iterator. -</li> -<li> -If -OutIter returns a proxy type with an overloaded operator&, this -definition probably won't compile. Lifting this limitation while -allowing value_type to have an overloaded operator& would be hard, but -is probably possible with careful overloading. I'm not sure it's worth -it. -</li> -<li> -This definition retains the prohibition on the use of volatile types for the result. -</li> -</ol> - -</blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -We don't deal with volatile in the library. -</p> -<p> -Jim: should we state that explicitly somewhere? -</p> -<p> -Beman: you might argue that clause 17 should say something about -volatile. However, if you want to raise we argument, we should open it -as a separate issue and consult with experts on concurrency. -</p> -<p> -Hinnant: actually, some library components do handle volatile, so we'd -need to be very careful about what we say in clause 17. -</p> -<p> -No objection to NAD. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - - <p><b>Proposed resolution:</b></p> - <p> - -In order to allow these algorithms to operate on volatile storage I -propose to change the expression so as to make it well-formed even for -pointers to volatile types. Specifically, I propose the following -changes to clauses 20 and 24. Change 20.6.4.1, p1 to read: - - </p> - <pre> - -<i>Effects</i>: - -typedef typename iterator_traits<ForwardIterator>::pointer pointer; -typedef typename iterator_traits<ForwardIterator>::value_type value_type; - -for (; first != last; ++result, ++first) - new (static_cast<void*>(const_cast<pointer>(&*result)) - value_type (*first); - - </pre> - <p> - -change 20.6.4.2, p1 to read - - </p> - <pre> - -<i>Effects</i>: - -typedef typename iterator_traits<ForwardIterator>::pointer pointer; -typedef typename iterator_traits<ForwardIterator>::value_type value_type; - -for (; first != last; ++result, ++first) - new (static_cast<void*>(const_cast<pointer>(&*first)) - value_type (*x); - - </pre> - <p> - -and change 20.6.4.3, p1 to read - - </p> - <pre> - -<i>Effects</i>: - -typedef typename iterator_traits<ForwardIterator>::pointer pointer; -typedef typename iterator_traits<ForwardIterator>::value_type value_type; - -for (; n--; ++first) - new (static_cast<void*>(const_cast<pointer>(&*first)) - value_type (*x); - - </pre> - <p> - -In addition, since there is no partial specialization for -<code>iterator_traits<volatile T*></code> I propose to add one -to parallel such specialization for <const T*>. Specifically, I -propose to add the following text to the end of 24.3.1, p3: - - </p> - <p> - -and for pointers to volatile as - - </p> - <pre> - -namespace std { -template<class T> struct iterator_traits<volatile T*> { -typedef ptrdiff_t difference_type; -typedef T value_type; -typedef volatile T* pointer; -typedef volatile T& reference; -typedef random_access_iterator_tag iterator_category; -}; -} - - </pre> - <p> - -Note that the change to <code>iterator_traits</code> isn't necessary -in order to implement the specialized algorithms in a way that allows -them to operate on volatile strorage. It is only necesassary in order -to specify their effects in terms of <code>iterator_traits</code> as -is done here. Implementations can (and some do) achieve the same -effect by means of function template overloading. - - </p> - - - - -<hr> -<h3><a name="583"></a>583. <tt>div()</tt> for unsigned integral types</h3> -<p><b>Section:</b> 26.8 [c.math] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2006-06-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.math">active issues</a> in [c.math].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -There is no <tt>div()</tt> function for unsigned integer types. -</p> -<p> -There are several possible resolutions. The simplest one is noted below. Other -possibilities include a templated solution. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add to 26.7 [lib.c.math] paragraph 8: -</p> - -<blockquote><pre> -struct udiv_t div(unsigned, unsigned); -struct uldiv_t div(unsigned long, unsigned long); -struct ulldiv_t div(unsigned long long, unsigned long long); -</pre></blockquote> - - - -<p><b>Rationale:</b></p><p> -Toronto: C99 does not have these unsigned versions because -the signed version exist just to define the implementation-defined behavior -of signed integer division. Unsigned integer division has no implementation-defined -behavior and thus does not need this treatment. -</p> - - - - -<hr> -<h3><a name="584"></a>584. missing int <tt>pow(int,int)</tt> functionality</h3> -<p><b>Section:</b> 26.8 [c.math] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2006-06-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.math">active issues</a> in [c.math].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -There is no <tt>pow()</tt> function for any integral type. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add something like: -</p> - -<blockquote><pre> -template< typename T> -T power( T x, int n ); -// requires: n >=0 -</pre></blockquote> - - -<p><b>Rationale:</b></p><p> -Toronto: We already have <tt>double pow(<i>integral</i>, <i>integral</i>)</tt> from 26.8 [c.math] p11. -</p> - - - - -<hr> -<h3><a name="585"></a>585. facet error reporting</h3> -<p><b>Section:</b> 22.4 [locale.categories] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor, Paolo Carlini <b>Opened:</b> 2006-06-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.categories">issues</a> in [locale.categories].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - <p> - -Section 22.2, paragraph 2 requires facet <code>get()</code> members -that take an <code>ios_base::iostate&</code> argument, -<code><i>err</i></code>, to ignore the (initial) value of the -argument, but to set it to <code>ios_base::failbit</code> in case of a -parse error. - - </p> - <p> - -We believe there are a few minor problems with this blanket -requirement in conjunction with the wording specific to each -<code>get()</code> member function. - - </p> - <p> - -First, besides <code>get()</code> there are other member functions -with a slightly different name (for example, -<code>get_date()</code>). It's not completely clear that the intent of -the paragraph is to include those as well, and at least one -implementation has interpreted the requirement literally. - - </p> - <p> - -Second, the requirement to "set the argument to -<code>ios_base::failbit</code> suggests that the functions are not -permitted to set it to any other value (such as -<code>ios_base::eofbit</code>, or even <code>ios_base::eofbit | -ios_base::failbit</code>). - - </p> - <p> - -However, 22.2.2.1.2, p5 (Stage 3 of <code>num_get</code> parsing) and -p6 (<code>bool</code> parsing) specifies that the <code>do_get</code> -functions perform <code><i>err</i> |= ios_base::eofbit</code>, which -contradicts the earlier requirement to ignore <i>err</i>'s initial -value. - - </p> - <p> - -22.2.6.1.2, p1 (the Effects clause of the <code>money_get</code> -facet's <code>do_get</code> member functions) also specifies that -<code><i>err</i></code>'s initial value be used to compute the final -value by ORing it with either <code>ios_base::failbit</code> or -with<code>ios_base::eofbit | ios_base::failbit</code>. - - </p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Move to NAD. -</p></blockquote> - - - - <p><b>Proposed resolution:</b></p> - <p> - -We believe the intent is for all facet member functions that take an -<code>ios_base::iostate&</code> argument to: - - </p> - <ul> - <li> - -ignore the initial value of the <code><i>err</i></code> argument, - - </li> - <li> - -reset <code><i>err</i></code> to <code>ios_base::goodbit</code> prior -to any further processing, - - </li> - <li> - -and set either <code>ios_base::eofbit</code>, or -<code>ios_base::failbit</code>, or both in <code><i>err</i></code>, as -appropriate, in response to reaching the end-of-file or on parse -error, or both. - - </li> - </ul> - <p> - -To that effect we propose to change 22.2, p2 as follows: - - </p> - <p> - -The <i>put</i><del>()</del> members make no provision for error -reporting. (Any failures of the OutputIterator argument must be -extracted from the returned iterator.) <ins>Unless otherwise -specified, </ins>the <i>get</i><del>()</del> members <ins>that</ins> -take an <code>ios_base::iostate&</code> argument <del>whose value -they ignore, but set to ios_base::failbit in case of a parse -error.</del><ins>, <code><i>err</i></code>, start by evaluating -<code>err = ios_base::goodbit</code>, and may subsequently set -<i>err</i> to either <code>ios_base::eofbit</code>, or -<code>ios_base::failbit</code>, or <code>ios_base::eofbit | -ios_base::failbit</code> in response to reaching the end-of-file or in -case of a parse error, or both, respectively.</ins> - - </p> - - -<p><i>[ -Kona (2007): We need to change the proposed wording to clarify that the -phrase "the get members" actually denotes <tt>get()</tt>, <tt>get_date()</tt>, etc. -Proposed Disposition: Open -]</i></p> - - - - -<hr> -<h3><a name="587"></a>587. iststream ctor missing description</h3> -<p><b>Section:</b> D.7.2.1 [depr.istrstream.cons] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2006-06-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - <p> - -The <code>iststream(char*, streamsize)</code> ctor is in the class -synopsis in D.7.2 but its signature is missing in the description -below (in D.7.2.1). - - </p> - - - <p><b>Proposed resolution:</b></p> - <p> - -This seems like a simple editorial issue and the missing signature can -be added to the one for <code>const char*</code> in paragraph 2. - - </p> - -<p><i>[ -post Oxford: Noted that it is already fixed in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2284.pdf">N2284</a> -]</i></p> - - - - - - -<hr> -<h3><a name="588"></a>588. requirements on zero sized <tt>tr1::arrays</tt> and other details</h3> -<p><b>Section:</b> 23.3.2 [array] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Gennaro Prota <b>Opened:</b> 2006-07-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#array">active issues</a> in [array].</p> -<p><b>View all other</b> <a href="lwg-index.html#array">issues</a> in [array].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The wording used for section 23.2.1 [lib.array] seems to be subtly -ambiguous about zero sized arrays (N==0). Specifically: -</p> -<p> -* "An instance of array<T, N> stores N elements of type T, so that -[...]" -</p> -<p> -Does this imply that a zero sized array object stores 0 elements, i.e. -that it cannot store any element of type T? The next point clarifies -the rationale behind this question, basically how to implement begin() -and end(): -</p> -<p> -* 23.2.1.5 [lib.array.zero], p2: "In the case that N == 0, begin() == -end() == unique value." -</p> -<p> -What does "unique" mean in this context? Let's consider the following -possible implementations, all relying on a partial specialization: -</p> -<blockquote><pre> -a) - template< typename T > - class array< T, 0 > { - - .... - - iterator begin() - { return iterator( reinterpret_cast< T * >( this ) ); } - .... - - }; -</pre></blockquote> -<p> -This has been used in boost, probably intending that the return value -had to be unique to the specific array object and that array couldn't -store any T. Note that, besides relying on a reinterpret_cast, has -(more than potential) alignment problems. -</p> -<blockquote><pre> -b) - template< typename T > - class array< T, 0 > { - - T t; - - iterator begin() - { return iterator( &t ); } - .... - - }; -</pre></blockquote> -<p> -This provides a value which is unique to the object and to the type of -the array, but requires storing a T. Also, it would allow the user to -mistakenly provide an initializer list with one element. -</p> -<p> -A slight variant could be returning *the* null pointer of type T -</p> -<blockquote><pre> - return static_cast<T*>(0); -</pre></blockquote> -<p> -In this case the value would be unique to the type array<T, 0> but not -to the objects (all objects of type array<T, 0> with the same value -for T would yield the same pointer value). -</p> -<p> -Furthermore this is inconsistent with what the standard requires from -allocation functions (see library issue 9). -</p> -<p> -c) same as above but with t being a static data member; again, the -value would be unique to the type, not to the object. -</p> -<p> -d) to avoid storing a T *directly* while disallowing the possibility -to use a one-element initializer list a non-aggregate nested class -could be defined -</p> -<blockquote><pre> - struct holder { holder() {} T t; } h; -</pre></blockquote> -<p> -and then begin be defined as -</p> -<blockquote><pre> - iterator begin() { return &h.t; } -</pre></blockquote> -<p> -But then, it's arguable whether the array stores a T or not. -Indirectly it does. -</p> -<p> ------------------------------------------------------ -</p> -<p> -Now, on different issues: -</p> -<p> -* what's the effect of calling assign(T&) on a zero-sized array? There -seems to be only mention of front() and back(), in 23.2.1 [lib.array] -p4 (I would also suggest to move that bullet to section 23.2.1.5 -[lib.array.zero], for locality of reference) -</p> -<p> -* (minor) the opening paragraph of 23.2.1 [lib.array] wording is a bit -inconsistent with that of other sequences: that's not a problem in -itself, but compare it for instance with "A vector is a kind of -sequence that supports random access iterators"; though the intent is -obvious one might argue that the wording used for arrays doesn't tell -what an array is, and relies on the reader to infer that it is what -the <array> header defines. -</p> -<p> -* it would be desiderable to have a static const data member of type -std::size_t, with value N, for usage as integral constant expression -</p> -<p> -* section 23.1 [lib.container.requirements] seem not to consider -fixed-size containers at all, as it says: "[containers] control -allocation and deallocation of these objects [the contained objects] -through constructors, destructors, *insert and erase* operations" -</p> -<p> -* max_size() isn't specified: the result is obvious but, technically, -it relies on table 80: "size() of the largest possible container" -which, again, doesn't seem to consider fixed size containers -</p> - -<p><i>[ -2009-05-29 Daniel adds: -]</i></p> - - -<blockquote> -<ol style="list-style-type:lower-alpha"> -<li> -<p> -star bullet 1 ("what's the effect of calling <tt>assign(T&)</tt> on a -zero-sized array?[..]"); -</p> -<blockquote><p> -<tt>assign</tt> has been renamed to <tt>fill</tt> and the semantic of <tt>fill</tt> is now -defined in terms of -the free algorithm <tt>fill_n</tt>, which is well-defined for this situation. -</p></blockquote> -</li> -<li> -<p> -star bullet 3 ("it would be desiderable to have a static const data -member..."): -</p> -<blockquote><p> -It seems that <tt>tuple_size<array<T, N> >::value</tt> as of 23.3.2.9 [array.tuple] does -provide this functionality now. -</p></blockquote> -</li> -</ol> -</blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -Alisdair to address by the next meeting, or declare NAD. -</p> -<p> -Moved to Tentatively NAD. -</p> -</blockquote> - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote><p> -Moved to NAD. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><i>[ -Kona (2007): requirements on zero sized <tt>tr1::array</tt>s and other details -Issue 617: <tt>std::array</tt> is a sequence that doesn't satisfy the sequence -requirements? Alisdair will prepare a paper. Proposed Disposition: Open -]</i></p> - - - - - -<hr> -<h3><a name="590"></a>590. Type traits implementation latitude should be removed for C++0x</h3> -<p><b>Section:</b> 20.10 [meta], TR1 4.9 [tr.meta.req] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2006-08-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#meta">active issues</a> in [meta].</p> -<p><b>View all other</b> <a href="lwg-index.html#meta">issues</a> in [meta].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -20.4.9 [lib.meta.req], Implementation requirements, provides latitude for type -traits implementers that is not needed in C++0x. It includes the wording: -</p> - -<blockquote><p> -[<i>Note:</i> the latitude granted to implementers in this clause is temporary, -and is expected to be removed in future revisions of this document. -- <i>end note</i>] -</p></blockquote> - -<p> -Note: -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2157.html">N2157: Minor Modifications to the type traits Wording</a> -also has the intent of removing this wording from the WP. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Remove 20.4.9 [lib.meta.req] in its entirety from the WP. -</p> - -<p><i>[ -post-Oxford: Recommend NAD Editorial. This resolution is now in the -current working draft. -]</i></p> - - - - - - - -<hr> -<h3><a name="591"></a>591. Misleading "built-in</h3> -<p><b>Section:</b> 18.3.2.4 [numeric.limits.members] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> whyglinux <b>Opened:</b> 2006-08-08 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#numeric.limits.members">issues</a> in [numeric.limits.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -18.2.1.2 numeric_limits members [lib.numeric.limits.members] -Paragraph 7: -</p> -<blockquote><p> -"For built-in integer types, the number of non-sign bits in the -representation." -</p></blockquote> - -<p> -26.1 Numeric type requirements [lib.numeric.requirements] -Footnote: -</p> - -<blockquote><p> -"In other words, value types. These include built-in arithmetic types, -pointers, the library class complex, and instantiations of valarray for -value types." -</p></blockquote> - -<p> -Integer types (which are bool, char, wchar_t, and the signed and -unsigned integer types) and arithmetic types (which are integer and -floating types) are all built-in types and thus there are no -non-built-in (that is, user-defined) integer or arithmetic types. Since -the redundant "built-in" in the above 2 sentences can mislead that -there may be built-in or user-defined integer and arithmetic types -(which is not correct), the "built-in" should be removed. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -18.2.1.2 numeric_limits members [lib.numeric.limits.members] -Paragraph 7: -</p> -<blockquote><p> -"For <del>built-in</del> integer types, the number of non-sign bits in the -representation." -</p></blockquote> - -<p> -26.1 Numeric type requirements [lib.numeric.requirements] -Footnote: -</p> - -<blockquote><p> -"In other words, value types. These include <del>built-in</del> arithmetic types, -pointers, the library class complex, and instantiations of valarray for -value types." -</p></blockquote> - - -<p><b>Rationale:</b></p> -<p> -Recommend NAD / Editorial. The proposed resolution is accepted as editorial. -</p> - - - - - -<hr> -<h3><a name="592"></a>592. Incorrect treatment of rdbuf()->close() return type</h3> -<p><b>Section:</b> 27.9.1.9 [ifstream.members] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Christopher Kohlhoff <b>Opened:</b> 2006-08-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ifstream.members">issues</a> in [ifstream.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I just spotted a minor problem in 27.8.1.7 -[lib.ifstream.members] para 4 and also 27.8.1.13 -[lib.fstream.members] para 4. In both places it says: -</p> -<blockquote> -<pre> -void close(); -</pre> -<p> -Effects: Calls rdbuf()->close() and, if that function returns false, ... -</p> -</blockquote> -<p> -However, basic_filebuf::close() (27.8.1.2) returns a pointer to the -filebuf on success, null on failure, so I think it is meant to -say "if that function returns a null pointer". Oddly, it is -correct for basic_ofstream. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 27.9.1.9 [ifstream.members], p5: -</p> - -<blockquote><p> -<i>Effects:</i> Calls <tt>rdbuf()->close()</tt> and, if that function -<ins>fails (</ins>returns <del><tt>false</tt></del> <ins>a null pointer)</ins>, -calls <tt>setstate(failbit)</tt> (which may throw <tt>ios_base::failure</tt> -(27.4.4.3)). -</p></blockquote> - -<p> -Change 27.9.1.17 [fstream.members], p5: -</p> - -<blockquote><p> -<i>Effects:</i> Calls <tt>rdbuf()->close()</tt> and, if that function -<ins>fails (</ins>returns <del><tt>false</tt></del> <ins>a null pointer)</ins>, -calls <tt>setstate(failbit)</tt> (which may throw <tt>ios_base::failure</tt> -(27.4.4.3)). -</p></blockquote> - - - -<p><i>[ -Kona (2007): Proposed Disposition: NAD, Editorial -]</i></p> - - - - - -<hr> -<h3><a name="597"></a>597. Decimal: The notion of 'promotion' cannot be emulated by user-defined types.</h3> -<p><b>Section:</b> TRDecimal 3.2 [trdec.types.types] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daveed Vandevoorde <b>Opened:</b> 2006-04-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#trdec.types.types">issues</a> in [trdec.types.types].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In a private email, Daveed writes: -</p> -<blockquote> -<p> -I am not familiar with the C TR, but my guess is that the -class type approach still won't match a built-in type -approach because the notion of "promotion" cannot be -emulated by user-defined types. -</p> -<p> -Here is an example: -</p> -</blockquote> -<pre> - - struct S { - S(_Decimal32 const&); // Converting constructor - }; - void f(S); - - void f(_Decimal64); - - void g(_Decimal32 d) { - f(d); - } -</pre> - -<blockquote> -<p> -If _Decimal32 is a built-in type, the call f(d) will likely -resolve to f(_Decimal64) because that requires only a -promotion, whereas f(S) requires a user-defined conversion. -</p> -<p> -If _Decimal32 is a class type, I think the call f(d) will be -ambiguous because both the conversion to _Decimal64 and the -conversion to S will be user-defined conversions with neither -better than the other. -</p> -</blockquote> -<p> -Robert comments: -</p> -<p> -In general, a library of arithmetic types cannot exactly emulate the behavior of the intrinsic numeric types. There are several ways to tell whether an implementation of the decimal types uses compiler intrinisics or a library. For example: -</p> -<pre> - _Decimal32 d1; - d1.operator+=(5); // If d1 is a builtin type, this won't compile. -</pre> -<p> -In preparing the decimal TR, we have three options: -</p> -<ol> -<li>require that the decimal types be class types</li> -<li>require that the decimal types be builtin types, like float and double</li> -<li>specify a library of class types, but allow enough implementor latitude that a conforming implementation could instead provide builtin types</li> -</ol> -<p> -We decided as a group to pursue option #3, but that approach implies that implementations may not agree on the semantics of certain use cases (first example, above), or on whether certain other cases are well-formed (second example). Another potentially important problem is that, under the present definition of POD, the decimal classes are not POD types, but builtins will be. -</p> -<p> -Note that neither example above implies any problems with respect to C-to-C++ compatibility, since neither example can be expressed in C. -</p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -Decimal numeric types may either be builtin types or library types. We -only intend to specify the common subset of behaviors of the two -implementation approaches. The front matter of the Decimal TR says this -explicitly. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="606"></a>606. Decimal: allow narrowing conversions</h3> -<p><b>Section:</b> TRDecimal 3.2 [trdec.types.types] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2006-06-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#trdec.types.types">issues</a> in [trdec.types.types].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In c++std-lib-17205, Martin writes: -</p> -<blockquote><p> -...was it a deliberate design choice to make narrowing assignments ill-formed while permitting narrowing compound assignments? For instance: -</p></blockquote> -<pre> - decimal32 d32; - decimal64 d64; - - d32 = 64; // error - d32 += 64; // okay -</pre> -<p> -In c++std-lib-17229, Robert responds: -</p> -<blockquote><p> -It is a vestige of an old idea that I forgot to remove from the paper. Narrowing assignments should be permitted. The bug is that the converting constructors that cause narrowing should not be explicit. Thanks for pointing this out. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -The current state of the Decimal TR is the result of a deliberate design -decision that has been examined many times. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -1. In "3.2.2 Class <code>decimal32</code>" synopsis, remove the <code>explicit</code> specifier from the narrowing conversions: -</p> -<pre> - // <i>3.2.2.2 conversion from floating-point type:</i> - <del>explicit</del> decimal32(decimal64 <i>d64</i>); - <del>explicit</del> decimal32(decimal128 <i>d128</i>); -</pre> -<p> -2. Do the same thing in "3.2.2.2. Conversion from floating-point type." -</p> -<p> -3. In "3.2.3 Class <code>decimal64</code>" synopsis, remove the <code>explicit</code> specifier from the narrowing conversion: -</p> -<pre> - // <i>3.2.3.2 conversion from floating-point type:</i> - <del>explicit</del> decimal64(decimal128 <i>d128</i>); -</pre> -<p> -4. Do the same thing in "3.2.3.2. Conversion from floating-point type." -</p> - -<p><i>[ -Redmond: We prefer explicit conversions for narrowing and implicit for widening. -]</i></p> - - - - - - -<hr> -<h3><a name="614"></a>614. <tt>std::string</tt> allocator requirements still inconsistent</h3> -<p><b>Section:</b> 21.4 [basic.string] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Bo Persson <b>Opened:</b> 2006-12-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#basic.string">active issues</a> in [basic.string].</p> -<p><b>View all other</b> <a href="lwg-index.html#basic.string">issues</a> in [basic.string].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -This is based on N2134, where 21.3.1/2 states: -"... The Allocator object used shall be a copy of the Allocator object -passed to the basic_string object's constructor or, if the constructor does -not take an Allocator argument, a copy of a default-constructed Allocator -object." -</p> -<p> -Section 21.3.2/1 lists two constructors: -</p> -<blockquote><pre> -basic_string(const basic_string<charT,traits,Allocator>& str ); - -basic_string(const basic_string<charT,traits,Allocator>& str , - size_type pos , size_type n = npos, - const Allocator& a = Allocator()); -</pre></blockquote> -<p> -and then says "In the first form, the Allocator value used is copied from -str.get_allocator().", which isn't an option according to 21.3.1. -</p> -<p><i>[ -Batavia: We need blanket statement to the effect of: -]</i></p> - - -<ol> -<li>If an allocator is passed in, use it, or,</li> -<li>If a string is passed in, use its allocator.</li> -</ol> -<p><i>[ -Review constructors and functions that return a string; make sure we follow these -rules (substr, operator+, etc.). Howard to supply wording. -]</i></p> - - -<p><i>[ -Bo adds: The new container constructor which takes only a <tt>size_type</tt> is not -consistent with 23.2 [container.requirements], p9 which says in part: -]</i></p> - - -<blockquote><p> -All other constructors for these container types take an -<tt>Allocator&</tt> argument (20.1.2), an allocator whose value type -is the same as the container's value type. A copy of this argument is -used for any memory allocation performed, by these constructors and by -all member functions, during the lifetime of each container object. -</p></blockquote> - -<p><i>[ -post Bellevue: We re-confirm that the issue is real. Pablo will provide wording. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Move to NAD. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="615"></a>615. Inconsistencies in Section 21.4</h3> -<p><b>Section:</b> 21.8 [c.strings] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Bo Persson <b>Opened:</b> 2006-12-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.strings">active issues</a> in [c.strings].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.strings">issues</a> in [c.strings].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In the current draft N2134, 21.4/1 says -</p> -<p> -"Tables 59,228) 60, 61, 62,and 63 229) 230) describe headers <cctype>, -<cwctype>, <cstring>, <cwchar>, and <cstdlib> (character conversions), -respectively." -</p> -<p> -Here footnote 229 applies to table 62, not table 63. -</p> -<p> -Also, footnote 230 lists the new functions in table 63, "atoll, strtoll, -strtoull, strtof, and strtold added by TR1". However, strtof is not present -in table 63. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p> -<p> -Recommend NAD, editorial. Send to Pete. -</p> - - - - - -<hr> -<h3><a name="617"></a>617. <tt>std::array</tt> is a sequence that doesn't satisfy the sequence requirements?</h3> -<p><b>Section:</b> 23.3.2 [array] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Bo Persson <b>Opened:</b> 2006-12-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#array">active issues</a> in [array].</p> -<p><b>View all other</b> <a href="lwg-index.html#array">issues</a> in [array].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The <tt><array></tt> header is given under 23.3 [sequences]. -23.3.2 [array]/paragraph 3 says: -</p> -<blockquote><p> -"Unless otherwise specified, all array operations are as described in -23.2 [container.requirements]". -</p></blockquote> -<p> -However, <tt>array</tt> isn't mentioned at all in section 23.2 [container.requirements]. -In particular, Table 82 "Sequence requirements" lists several operations (insert, erase, clear) -that <tt>std::array</tt> does not have in 23.3.2 [array]. -</p> -<p> -Also, Table 83 "Optional sequence operations" lists several operations that -<tt>std::array</tt> does have, but array isn't mentioned. -</p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -The real issue seems to be different than what is described here. -Non-normative text says that <tt>std::array</tt> is a sequence container, but -there is disagreement about what that really means. There are two -possible interpretations: -</p> -<ol> -<li> -a sequence container is one that satisfies all sequence container requirements -</li> -<li> -a sequence container is one that satisfies some of the sequence -container requirements. Any operation that the container supports is -specified by one or more sequence container requirements, unless that -operation is specifically singled out and defined alongside the -description of the container itself. -</li> -</ol> -<p> -Move to Tentatively NAD. -</p> -</blockquote> - -<p><i>[ -2009-07-15 Loïc Joly adds: -]</i></p> - - -<blockquote> -<p> -The section 23.2.3 [sequence.reqmts]/1 states that array is a sequence. 23.2.3 [sequence.reqmts]/3 -introduces table 83, named Sequence container requirements. This seems -to me to be defining the requirements for all sequences. However, array -does not follow all of this requirements (this can be read in the array -specific section, for the standard is currently inconsistent). -</p> - -<p> -Proposed resolution 1 (minimal change): -</p> -<blockquote> -<p> -Say that array is a container, that in addition follows only some of the -sequence requirements, as described in the array section: -</p> - -<blockquote><p> -The library provides <del>five</del> <ins>three</ins> basic kinds of sequence containers: <del><tt>array</tt></del>, -<tt>vector</tt>, -<del><tt>forward_list</tt></del>, <tt>list</tt>, and <tt>deque</tt>. <ins>In addition, <tt>array</tt> -and <tt>forward_list</tt> follows some of the requirements -of sequences, as described in their respective sections.</ins> -</p></blockquote> - -</blockquote> - -<p> -Proposed resolution 2 (most descriptive description, no full wording provided): -</p> -<blockquote><p> -Introduce the notion of a Fixed Size Sequence, with it requirement table -that would be a subset of the current Sequence container. array would be -the only Fixed Size Sequence (but dynarray is in the queue for TR2). -Sequence requirements would now be requirements in addition to Fixed -Size Sequence requirements (it is currently in addition to container). -</p></blockquote> -</blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Move to NAD Editorial -</p></blockquote> - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote><p> -This will require a lot of reorganization. Editor doesn't think this is really -an issue, since the description of array can be considered as overriding -what's specified about sequences. Move to NAD. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="626"></a>626. new <i>Remark</i> clauses not documented</h3> -<p><b>Section:</b> 17.5.1.4 [structure.specifications] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2007-01-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#structure.specifications">issues</a> in [structure.specifications].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - <p> - -The <i>Remark</i> clauses newly introduced into the Working Paper -(<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2134.pdf">N2134</a>) -are not mentioned in 17.5.1.4 [structure.specifications] where we list the -meaning of <i>Effects</i>, <i>Requires</i>, and other clauses (with -the exception of <i>Notes</i> which are documented as informative in -17.5.1.2 [structure.summary], p2, and which they replace in many cases). - - </p> - <p> - -Propose add a bullet for <i>Remarks</i> along with a brief description. - - </p> -<p><i>[ -Batavia: Alan and Pete to work. -]</i></p> - - -<p><i>[ -Bellevue: Already resolved in current working paper. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="627"></a>627. Low memory and exceptions</h3> -<p><b>Section:</b> 18.6.1.1 [new.delete.single] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2007-01-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#new.delete.single">issues</a> in [new.delete.single].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I recognize the need for nothrow guarantees in the exception reporting -mechanism, but I strongly believe that implementors also need an escape hatch -when memory gets really low. (Like, there's not enough heap to construct and -copy exception objects, or not enough stack to process the throw.) I'd like to -think we can put this escape hatch in 18.6.1.1 [new.delete.single], -<tt>operator new</tt>, but I'm not sure how to do it. We need more than a -footnote, but the wording has to be a bit vague. The idea is that if -<tt>new</tt> can't allocate something sufficiently small, it has the right to -<tt>abort</tt>/call <tt>terminate</tt>/call <tt>unexpected</tt>. -</p> - -<p><i>[ -Bellevue: NAD. 1.4p2 specifies a program must behave correctly "within -its resource limits", so no further escape hatch is necessary. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="631"></a>631. conflicting requirements for <tt>BinaryPredicate</tt></h3> -<p><b>Section:</b> 25 [algorithms] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> James Kanze <b>Opened:</b> 2007-01-31 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#algorithms">active issues</a> in [algorithms].</p> -<p><b>View all other</b> <a href="lwg-index.html#algorithms">issues</a> in [algorithms].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The general requirements for <tt><tt>BinaryPredicate</tt></tt> (in 25 [algorithms]/8) contradict the implied specific requirements for -some functions. In particular, it says that: -</p> - -<blockquote><p> -[...] if an algorithm takes <tt>BinaryPredicate <i>binary_pred</i></tt> -as its argument and <tt><i>first1</i></tt> and <i>first2</i> as its -iterator arguments, it should work correctly in the construct <tt>if -(binary_pred (*<i>first1</i> , *<i>first2</i> )){...}</tt>. -<tt>BinaryPredicate</tt> always takes the first iterator type as its -first argument, that is, in those cases when <tt>T <i>value</i></tt> is -part of the signature, it should work correctly in the context of <tt>if -(binary_pred (*<i>first1</i> , <i>value</i>)){...}</tt>. -</p></blockquote> - -<p> -In the description of <tt>upper_bound</tt> (25.4.3.2 [upper.bound]/2), however, the use is described as -"<tt>!comp(<i>value</i>, <i>e</i>)</tt>", where <tt><i>e</i></tt> is an -element of the sequence (a result of dereferencing -<tt>*<i>first</i></tt>). -</p> - -<p> -In the description of <tt>lexicographical_compare</tt>, we have both -"<tt>*<i>first1</i> < *<i>first2</i></tt>" and "<tt>*<i>first2</i> -< *<i>first1</i></tt>" (which presumably implies "<tt>comp( -*<i>first1</i>, *<i>first2</i> )</tt>" and "<tt>comp( *<i>first2</i>, -*<i>first1</i> )</tt>". -</p> - -<p> -Logically, the <tt>BinaryPredicate</tt> is used as an ordering -relationship, with the semantics of "less than". Depending on the -function, it may be used to determine equality, or any of the inequality -relationships; doing this requires being able to use it with either -parameter first. I would thus suggest that the requirement be: -</p> - -<p> -Alternatively, one could specify an order for each function. IMHO, this -would be more work for the committee, more work for the implementors, -and of no real advantage for the user: some functions, such as -<tt>lexicographical_compare</tt> or <tt>equal_range</tt>, will still require both -functions, and it seems like a much easier rule to teach that both -functions are always required, rather than to have a complicated list of -when you only need one, and which one. -</p> - -<p><i>[ -Toronto: Moved to Open. ConceptGCC seems to get <tt>lower_bound</tt> -and <tt>upper_bound</tt> to work withoutt these changes. -]</i></p> - - -<p><i>[ -2009-07-28 Reopened by Alisdair. No longer solved by concepts. -]</i></p> - - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Move to Review. The small problem with the "iterator type" -will be fixed. The cited functions (<tt>lower_bound</tt>, <tt>uppwer_bound</tt>, -<tt>equal_range</tt>) don't actually use <tt>BinaryPredicate</tt> , and where it is used, -it is consistent with [algorithm]/8, so the main complaint of the issue -is moot. -</p></blockquote> - -<p><i>[ -2010-01-16 Beman clarified wording. -]</i></p> - - -<p><i>[ -2010-01-31: Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p><i>[ -post San Francisco: -]</i></p> - - -<blockquote> -<p> -Solved by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2759.pdf">N2759</a>. -</p> -</blockquote> - -<p> -2010-01-31: The draft standard is well specified as is, and this specification -is desired. Issues <a href="lwg-defects.html#556">556</a> and <a href="lwg-defects.html#870">870</a> solve the remaining -unclearness regarding the meaning of BinaryPredicate. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p><i>Change 25 [algorithms] paragraph 8 as indicated:</i></p> - -<blockquote> - -<p> -8 The <tt>BinaryPredicate</tt> parameter is used whenever an algorithm expects a -function object that when applied to the result of dereferencing two -corresponding iterators or to dereferencing an iterator and type <tt>T</tt> when -<tt>T</tt> is part of the signature returns a value testable as true. <ins> -<tt>BinaryPredicate</tt> always takes the first iterator <tt>value_type</tt> as -one of its arguments; which argument is unspecified.</ins> <del>In other words, -if</del> <ins> If</ins> an algorithm takes <tt>BinaryPredicate binary_pred</tt> -as its argument and <tt>first1</tt> and <tt>first2</tt> as its iterator -arguments, it should work correctly <ins>both</ins> in the construct <tt>if -(binary_pred(*first1, *first2)){...}</tt> <ins>and <tt>if (binary_pred (*first2, -*first1)){...}</tt></ins>. <del><tt>BinaryPredicate</tt> always takes the first -iterator type as its first argument, that is, in</del> <ins>In</ins> those cases -when <tt>T value</tt> is part of the signature, it should work correctly in the -context of <tt> if (binary_pred(*first1, value)){...}</tt> <ins>and of <tt>if -(binary_pred (value, *first1)){...}</tt></ins>. <del> <tt>binary_pred</tt> shall -not apply any non-constant function through the dereferenced iterators.</del> -<ins>[<i>Note:</i> if the two types are not identical, and neither is -convertable to the other, this may require that the <tt>BinaryPredicate</tt> be -a functional object with two overloaded <tt>operator()()</tt> functions. -— <i>end note</i>]</ins> -</p> - -</blockquote> - - - - - - -<hr> -<h3><a name="632"></a>632. Time complexity of <tt>size()</tt> for <tt>std::set</tt></h3> -<p><b>Section:</b> 23.2 [container.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Lionel B <b>Opened:</b> 2007-02-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#container.requirements">active issues</a> in [container.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#container.requirements">issues</a> in [container.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -A recent news group discussion: -</p> -<blockquote> -<p> -Anyone know if the Standard has anything to say about the time complexity -of <tt>size()</tt> for <tt>std::set</tt>? I need to access a set's size (<em>not</em> -to know if it is empty!) heavily during an algorithm and was thus wondering -whether I'd be better off tracking the size "manually" or whether that'd be pointless. -</p> -<p> -That would be pointless. <tt>size()</tt> is O(1). -</p> -<p> -Nit: the standard says "should" have constant time. Implementations may take -license to do worse. I know that some do this for <tt>std::list<></tt> as a part of -some trade-off with other operation. -</p> - -<p> -I was aware of that, hence my reluctance to use size() for std::set. -</p> -<p> -However, this reason would not apply to <tt>std::set<></tt> as far as I can see. -</p> -<p> -Ok, I guess the only option is to try it and see... -</p> -</blockquote> - -<p> -If I have any recommendation to the C++ Standards Committee it is that -implementations must (not "should"!) document clearly[1], where known, the -time complexity of *all* container access operations. -</p> -<p> -[1] In my case (gcc 4.1.1) I can't swear that the time complexity of size() -for std::set is not documented... but if it is it's certainly well hidden -away. -</p> - -<p><i>[ -Kona (2007): This issue affects all the containers. We'd love to see a -paper dealing with the broad issue. We think that the complexity of the -<tt>size()</tt> member of every container -- except possibly <tt>list</tt> -- should be -O(1). Alan has volunteered to provide wording. -]</i></p> - - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Mandating O(1) size will not fly, too many implementations would be -invalidated. Alan to provide wording that toughens wording, but that -does not absolutely mandate O(1). -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We observed that the wording "should" (in note a) has no effect. -Howard prefers that O(1) size be mandated. -It is not clear that this issue can be resolved to everyone's satisfaction, -but Alan will provide wording nonetheless. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Fixed by paper N2923. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="633"></a>633. Return clause mentions undefined "type()"</h3> -<p><b>Section:</b> 20.9.12.2.5 [func.wrap.func.targ] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-02-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -20.9.12.2.5 [func.wrap.func.targ], p4 says: -</p> -<blockquote><p> -<i>Returns:</i> If <tt>type() == typeid(T)</tt>, a pointer to the stored -function target; otherwise a null pointer. -</p></blockquote> - -<ol> -<li> -There exists neither a type, a typedef <tt>type</tt>, nor member -function <tt>type()</tt> in class template function nor in the global or -<tt>std</tt> namespace. -</li> -<li> -Assuming that <tt>type</tt> should have been <tt>target_type()</tt>, -this description would lead to false results, if <tt>T = <i>cv</i> -void</tt> due to returns clause 20.9.12.2.5 [func.wrap.func.targ], p1. -</li> -</ol> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 20.9.12.2.5 [func.wrap.func.targ], p4: -</p> - -<blockquote><p> -<i>Returns:</i> If <tt><del>type()</del> <ins>target_type()</ins> == typeid(T) <ins>&& typeid(T) != -typeid(void)</ins></tt>, a pointer to the stored function target; -otherwise a null pointer. -</p></blockquote> - -<p><i>[ -Pete: Agreed. It's editorial, so I'll fix it. -]</i></p> - - - - - - - -<hr> -<h3><a name="636"></a>636. 26.5.2.3 valarray::operator[]</h3> -<p><b>Section:</b> 26.6.2.4 [valarray.access] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Bo Persson <b>Opened:</b> 2007-02-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#valarray.access">issues</a> in [valarray.access].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The signature of the const operator[] has been changed to return a const -reference. -</p> -<p> -The description in paragraph 1 still says that the operator returns by -value. -</p> -<p><i>[ -Pete recommends editorial fix. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="637"></a>637. [c.math]/10 inconsistent return values</h3> -<p><b>Section:</b> 26.8 [c.math] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Bo Persson <b>Opened:</b> 2007-02-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.math">active issues</a> in [c.math].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -26.8 [c.math], paragraph 10 has long lists of added signatures for float and long double -functions. All the signatures have float/long double return values, which is -inconsistent with some of the double functions they are supposed to -overload. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 26.8 [c.math], paragraph 10, -</p> - -<blockquote><pre> -<del>float</del> <ins>int</ins> ilogb(float); -<del>float</del> <ins>long</ins> lrint(float); -<del>float</del> <ins>long</ins> lround(float); -<del>float</del> <ins>long long</ins> llrint(float); -<del>float</del> <ins>long long</ins> llround(float); - -<del>long double</del> <ins>int</ins> ilogb(long double); -<del>long double</del> <ins>long</ins> lrint(long double); -<del>long double</del> <ins>long</ins> lround(long double); -<del>long double</del> <ins>long long</ins> llrint(long double); -<del>long double</del> <ins>long long</ins> llround(long double); -</pre></blockquote> - - - - - -<hr> -<h3><a name="639"></a>639. Still problems with exceptions during streambuf IO</h3> -<p><b>Section:</b> 27.7.2.2.3 [istream::extractors], 27.7.3.6.3 [ostream.inserters] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-02-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#istream::extractors">issues</a> in [istream::extractors].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -There already exist two active DR's for the wording of 27.7.2.2.3 [istream::extractors]/13 -from 14882:2003(E), namely <a href="lwg-defects.html#64">64</a> and <a href="lwg-defects.html#413">413</a>. -</p> - -<p> -Even with these proposed corrections, already maintained in N2134, -I have the feeling, that the current wording does still not properly -handle the "exceptional" situation. The combination of para 14 -</p> - -<blockquote><p> -"[..] Characters are extracted and inserted until -any of the following occurs: -</p> -<p> -[..] -</p> -<p> -- an exception occurs (in which case the exception is caught)." -</p></blockquote> - -<p> -and 15 -</p> - -<blockquote><p> -"If the function inserts no characters, it calls setstate(failbit), -which -may throw ios_base::failure (27.4.4.3). If it inserted no characters -because it caught an exception thrown while extracting characters -from *this and failbit is on in exceptions() (27.4.4.3), then the -caught -exception is rethrown." -</p></blockquote> - -<p> -both in N2134 seems to imply that any exception, which occurs -*after* at least one character has been inserted is caught and lost -for -ever. It seems that even if failbit is on in exceptions() rethrow is -not -allowed due to the wording "If it inserted no characters because it -caught an exception thrown while extracting". -</p> - -<p> -Is this behaviour by design? -</p> - -<p> -I would like to add that its output counterpart in 27.7.3.6.3 [ostream.inserters]/7-9 -(also -N2134) does not demonstrate such an exception-loss-behaviour. -On the other side, I wonder concerning several subtle differences -compared to input:: -</p> -<p> -1) Paragraph 8 says at its end: -</p> - -<blockquote><p> -"- an exception occurs while getting a character from sb." -</p></blockquote> - -<p> -Note that there is nothing mentioned which would imply that such -an exception will be caught compared to 27.7.2.2.3 [istream::extractors]/14. -</p> - -<p> -2) Paragraph 9 says: -</p> - -<blockquote><p> -"If the function inserts no characters, it calls setstate(failbit) -(which -may throw ios_base::failure (27.4.4.3)). If an exception was thrown -while extracting a character, the function sets failbit in error -state, -and if failbit is on in exceptions() the caught exception is -rethrown." -</p></blockquote> - -<p> -The sentence starting with "If an exception was thrown" seems to -imply that such an exception *should* be caught before. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -(a) In 27.7.2.2.3 [istream::extractors]/15 (N2134) change the sentence -</p> - -<blockquote><p> -If the function inserts no characters, it calls -<tt>setstate(failbit)</tt>, which may throw <tt>ios_base::failure</tt> -(27.4.4.3). If <del>it inserted no characters because it caught an -exception thrown while extracting characters from <tt>*this</tt></del> -<ins>an exception was thrown while extracting a character from -<tt>*this</tt>, the function sets <tt>failbit</tt> in error state,</ins> -and <tt>failbit</tt> is on in <tt>exceptions()</tt> (27.4.4.3), then the -caught exception is rethrown. -</p></blockquote> - -<p> -(b) In 27.7.3.6.3 [ostream.inserters]/8 (N2134) change the sentence: -</p> - -<blockquote> -<p> -Gets characters from <tt>sb</tt> and inserts them in <tt>*this</tt>. -Characters are read from <tt>sb</tt> and inserted until any of the -following occurs: -</p> -<ul> -<li>end-of-file occurs on the input sequence;</li> -<li>inserting in the output sequence fails (in which case the character to be inserted is not extracted);</li> -<li>an exception occurs while getting a character from <tt>sb</tt> <ins>(in which -case the exception is caught)</ins>.</li> -</ul> -</blockquote> - - - -<p><b>Rationale:</b></p><p> -This extractor is described as a formatted input function so the -exception behavior is already specified. There is additional behavior -described in this section that applies to the case in which failbit is -set. This doesn't contradict the usual exception behavior for formatted -input functions because that applies to the case in which badbit is set. -</p> - - - - -<hr> -<h3><a name="641"></a>641. Editorial fix for 27.6.4 (N2134)</h3> -<p><b>Section:</b> 27.7.5 [ext.manip] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-02-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ext.manip">issues</a> in [ext.manip].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The function <tt>f</tt> in para 4 (27.7.5 [ext.manip]) references an unknown <tt>strm</tt> -in the following line: -</p> - -<blockquote><pre> -mg.get(Iter(str.rdbuf()), Iter(), intl, strm, err, mon); -</pre></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 27.7.5 [ext.manip], p4: -</p> - -<blockquote><pre> -mg.get(Iter(str.rdbuf()), Iter(), intl, str<del>m</del>, err, mon); -</pre></blockquote> - -<p><i>[ -Oxford: Editorial. -]</i></p> - - - - - - - -<hr> -<h3><a name="642"></a>642. Invalidated fstream footnotes in N2134</h3> -<p><b>Section:</b> 27.9.1.9 [ifstream.members], 27.9.1.13 [ofstream.members] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-02-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ifstream.members">issues</a> in [ifstream.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The standard wording of N2134 has extended the 14882:2003(E) -wording for the ifstream/ofstream/fstream open function to fix -a long standing problem, see <a href="lwg-defects.html#409">409</a>. -</p> - -<p> -Now it's properly written as -</p> - -<blockquote><p> -"If that function does not return a null pointer calls clear(), -otherwise -calls setstate(failbit)[..]" -</p></blockquote> - -<p> -instead of the previous -</p> - -<blockquote><p> -"If that function returns a null pointer, calls setstate(failbit)[..] -</p></blockquote> - -<p> -While the old footnotes saying -</p> - -<blockquote><p> -"A successful open does not change the error state." -</p></blockquote> - -<p> -where correct and important, they are invalid now for ifstream and -ofstream (because clear *does* indeed modify the error state) and -should be removed (Interestingly fstream itself never had these, -although -they where needed for that time). -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In 27.9.1.9 [ifstream.members], remove footnote: -</p> - -<blockquote><p> -<del><sup>334)</sup> A successful open does not change the error state.</del> -</p></blockquote> - -<p> -In 27.9.1.13 [ofstream.members], remove footnote: -</p> - -<blockquote><p> -<del><sup>335)</sup> A successful open does not change the error state.</del> -</p></blockquote> - - - - - - -<hr> -<h3><a name="644"></a>644. Possible typos in 'function' description</h3> -<p><b>Section:</b> 20.9.12.2 [func.wrap.func] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Bo Persson <b>Opened:</b> 2007-02-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#func.wrap.func">active issues</a> in [func.wrap.func].</p> -<p><b>View all other</b> <a href="lwg-index.html#func.wrap.func">issues</a> in [func.wrap.func].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -20.9.12.2 [func.wrap.func] -</p> -<p> -The note in paragraph 2 refers to 'undefined void operators', while the -section declares a pair of operators returning <tt>bool</tt>. -</p> - -<p><i>[ -Post-Sophia Antipolis: -]</i></p> - - -<blockquote><p> -Changed from Pending WP to Open. This issue was voted to WP at the same time the operators were -changed from private to deleted. The two issues stepped on each other. What do we want the return -type of these deleted functions to be? -</p></blockquote> - -<p><i>[ -2009-05-02 Daniel adds: -]</i></p> - - -<blockquote> -<p> -I suggest harmonizing this issue with similar classes. E.g. in -20.8.2.3 [util.smartptr.weak] <tt>bool</tt> return values for -</p> -<blockquote><pre> -template <class Y> bool operator<(weak_ptr<Y> const&) const = delete; -template <class Y> bool operator<=(weak_ptr<Y> const&) const = delete; -template <class Y> bool operator>(weak_ptr<Y> const&) const = delete; -template <class Y> bool operator>=(weak_ptr<Y> const&) const = delete; -</pre></blockquote> - -<p> -are used and basically all <em>newer</em> provided deleted copy assignment operators -of type <tt>X</tt> use the canonical return type <tt>X&</tt> instead of <tt>void</tt>. Since the note -mentioned in the issue description has now already been changed to -</p> -<blockquote><p> -deleted overloads close possible hole in the type system -</p></blockquote> -<p> -it seems to be of even lesser need to perform the change. Therefore -I recommend declaring the issue as NAD. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree with Daniel's recommendation. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 20.9.12.2 [func.wrap.func] -</p> - -<blockquote><pre> -... -private: - // 20.9.12.2 [func.wrap.func], undefined operators: - template<class Function2> <del>bool</del> <ins>void</ins> operator==(const function<Function2>&); - template<class Function2> <del>bool</del> <ins>void</ins> operator!=(const function<Function2>&); -}; -</pre></blockquote> - -<p> -Change 20.9.12.2 [func.wrap.func] -</p> - -<blockquote><pre> -template<class Function2> <del>bool</del> <ins>void</ins> operator==(const function<Function2>&); -template<class Function2> <del>bool</del> <ins>void</ins> operator!=(const function<Function2>&); -</pre></blockquote> - - - - - -<hr> -<h3><a name="645"></a>645. Missing members in match_results</h3> -<p><b>Section:</b> 28.10 [re.results] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-02-26 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#re.results">issues</a> in [re.results].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -According to the description given in 28.10 [re.results]/2 the class template -match_results "shall satisfy the requirements of a Sequence, [..], -except that only operations defined for const-qualified Sequences -are supported". -Comparing the provided operations from 28.10 [re.results]/3 with the -sequence/container tables 80 and 81 one recognizes the following -missing operations: -</p> - -<p> -1) The members -</p> - -<blockquote><pre> -const_iterator rbegin() const; -const_iterator rend() const; -</pre></blockquote> - -<p> -should exists because 23.1/10 demands these for containers -(all sequences are containers) which support bidirectional -iterators. Aren't these supported by match_result? This is not -explicitely expressed, but it's somewhat implied by two arguments: -</p> -<p> -(a) Several typedefs delegate to -<tt>iterator_traits<BidirectionalIterator></tt>. -</p> -<p> -(b) The existence of <tt>const_reference operator[](size_type n) const</tt> -implies even random-access iteration. -I also suggest, that <tt>match_result</tt> should explicitly mention, -which minimum iterator category is supported and if this does -not include random-access the existence of <tt>operator[]</tt> is -somewhat questionable. -</p> -<p> -2) The new "convenience" members -</p> -<blockquote><pre> -const_iterator cbegin() const; -const_iterator cend() const; -const_iterator crbegin() const; -const_iterator crend() const; -</pre></blockquote> -<p> -should be added according to tables 80/81. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add the following members to the <tt>match_results</tt> synopsis after <tt>end()</tt> in 28.10 [re.results] -para 3: -</p> - -<blockquote><pre> -const_iterator cbegin() const; -const_iterator cend() const; -</pre></blockquote> - -<p> -In section 28.10.4 [re.results.acc] change: -</p> - -<blockquote> -<pre> -const_iterator begin() const; -<ins>const_iterator cbegin() const;</ins> -</pre> -<blockquote> -<p> --7- <i>Returns:</i> A starting iterator that enumerates over all the sub-expressions stored in <tt>*this</tt>. -</p> -</blockquote> - -<pre> -const_iterator end() const; -<ins>const_iterator cend() const;</ins> -</pre> -<blockquote> -<p> --8- <i>Returns:</i> A terminating iterator that enumerates over all the sub-expressions stored in <tt>*this</tt>. -</p> -</blockquote> -</blockquote> - - - -<p><i>[ -Kona (2007): Voted to adopt proposed wording in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2409.pdf">N2409</a> -except removing the entry in the table container requirements. Moved to Review. -]</i></p> - - -<p><i>[ -Bellevue: Proposed wording now in the WP. -]</i></p> - - - - - -<hr> -<h3><a name="647"></a>647. Inconsistent <tt>regex_search</tt> params</h3> -<p><b>Section:</b> 28.11.3 [re.alg.search] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-02-26 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -28.11.3 [re.alg.search]/5 declares -</p> - -<blockquote><pre> -template <class iterator, class charT, class traits> -bool regex_search(iterator first, iterator last, - const basic_regex<charT, traits>& e, - regex_constants::match_flag_type flags = - regex_constants::match_default); -</pre></blockquote> - -<p> -where it's not explained, which iterator category -the parameter iterator belongs to. This is inconsistent -to the preceding declaration in the synopsis section -28.4 [re.syn], which says: -</p> - -<blockquote><pre> -template <class BidirectionalIterator, class charT, class traits> -bool regex_search(BidirectionalIterator first, BidirectionalIterator last, - const basic_regex<charT, traits>& e, - regex_constants::match_flag_type flags = - regex_constants::match_default); -</pre></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -In 28.11.3 [re.alg.search]/5 replace all three occurences of param "iterator" with -"BidirectionalIterator" -</p> - -<blockquote><pre> -template <class <del>iterator</del> <ins>BidirectionalIterator</ins>, class charT, class traits> - bool regex_search(<del>iterator</del> <ins>BidirectionalIterator</ins> first, <del>iterator</del> <ins>BidirectionalIterator</ins> last, - const basic_regex<charT, traits>& e, - regex_constants::match_flag_type flags = - regex_constants::match_default); -</pre> -<p> --6- <i>Effects:</i> Behaves "as if" by constructing an object what of -type <tt>match_results<<del>iterator</del> -<ins>BidirectionalIterator</ins>></tt> and then returning the result -of <tt>regex_search(first, last, what, e, flags)</tt>. -</p> -</blockquote> - - -<p><b>Rationale:</b></p><p> -Applied to working paper while issue was still in New status. -</p> - - - - -<hr> -<h3><a name="648"></a>648. regex_iterator c'tor needs clarification/editorial fix</h3> -<p><b>Section:</b> 28.12.1.1 [re.regiter.cnstr] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-03-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In 28.12.1.1 [re.regiter.cnstr]/2 the effects paragraph starts with: -</p> - -<blockquote> -<p> -<i>Effects:</i> Initializes begin and end to point to the beginning and the -end of the target sequence, sets pregex to &re, sets flags to f,[..] -</p></blockquote> - -<p> -There are two issues with this description: -</p> - -<ol> -<li> -The meaning of very first part of this quote is unclear, because -there is no target sequence provided, instead there are given two -parameters a and b, both of type BidirectionalIterator. The mentioned -part does not explain what a and b represent. -</li> -<li> -There does not exist any parameter f, but instead a parameter -m in the constructor declaration, so this is actually an editorial -fix. -</li> -</ol> - - -<p><b>Proposed resolution:</b></p> -<p> -In 28.12.1.1 [re.regiter.cnstr]/2 change the above quoted part by -</p> - -<blockquote><p> -<i>Effects:</i> Initializes <tt>begin</tt> and <tt>end</tt> to point to -the beginning and the end of the target sequence <ins>designated by the -iterator range <tt>[a, b)</tt></ins>, sets <tt>pregex</tt> to -<tt>&re</tt>, sets <tt>flags</tt> to <tt><del>f</del> -<ins>m</ins></tt>, then calls <tt>regex_search(begin, end, match, -*pregex, flags)</tt>. If this call returns <tt>false</tt> the -constructor sets <tt>*this</tt> to the end-of-sequence iterator. -</p></blockquote> - - - - - -<hr> -<h3><a name="649"></a>649. Several typos in regex_token_iterator constructors</h3> -<p><b>Section:</b> 28.12.2.1 [re.tokiter.cnstr] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-03-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#re.tokiter.cnstr">issues</a> in [re.tokiter.cnstr].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In 28.12.2.1 [re.tokiter.cnstr]/1+2 both the constructor declaration -and the following text shows some obvious typos: -</p> -<p> -1) The third constructor form is written as -</p> -<blockquote><pre> -template <std::size_t N> - regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b, - const regex_type& re, - const int (&submatches)[R], - regex_constants::match_flag_type m = - regex_constants::match_default); -</pre></blockquote> - -<p> -where the dimensions of submatches are specified by an -unknown value R, which should be N. -</p> -<p> -2) Paragraph 2 of the same section says in its last sentence: -</p> - -<blockquote><p> -The third constructor initializes the member <tt>subs</tt> to hold a -copy of the sequence of integer values pointed to by the iterator range -<tt>[&submatches, &submatches + R)</tt>. -</p></blockquote> - -<p> -where again R must be replaced by N. -</p> - -<p> -3) Paragraph 3 of the same section says in its first sentence: -</p> - -<blockquote><p> -Each constructor then sets <tt>N</tt> to <tt>0</tt>, and -<tt>position</tt> to <tt>position_iterator(a, b, re, f)</tt>. -</p></blockquote> - -<p> -where a non-existing parameter "f" is mentioned, which must be -replaced -by the parameter "m". -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 28.12.2.1 [re.tokiter.cnstr]/1: -</p> -<blockquote><pre> -template <std::size_t N> - regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b, - const regex_type& re, - const int (&submatches)[<del>R</del> <ins>N</ins>], - regex_constants::match_flag_type m = - regex_constants::match_default); -</pre></blockquote> - -<p> -Change 28.12.2.1 [re.tokiter.cnstr]/2: -</p> - -<blockquote><p> -<i>Effects:</i> The first constructor initializes the member -<tt>subs</tt> to hold the single value <tt>submatch</tt>. The second -constructor initializes the member <tt>subs</tt> to hold a copy of the -argument <tt>submatches</tt>. The third constructor initializes the -member <tt>subs</tt> to hold a copy of the sequence of integer values -pointed to by the iterator range <tt>[&submatches, &submatches + -<del>R</del> <ins>N</ins>)</tt>. -</p></blockquote> - -<p> -Change 28.12.2.1 [re.tokiter.cnstr]/3: -</p> - -<blockquote><p> -Each constructor then sets <tt>N</tt> to <tt>0</tt>, and -<tt>position</tt> to <tt>position_iterator(a, b, re, <del>f</del> -<ins>m</ins>)</tt>. If <tt>position</tt> is not an end-of-sequence -iterator the constructor sets <tt>result</tt> to the address of the -current match. Otherwise if any of the values stored in <tt>subs</tt> is -equal to <tt>-1</tt> the constructor sets <tt>*this</tt> to a suffix -iterator that points to the range <tt>[a, b)</tt>, otherwise the -constructor sets <tt>*this</tt> to an end-of-sequence iterator. -</p></blockquote> - - - - - - -<hr> -<h3><a name="653"></a>653. Library reserved names</h3> -<p><b>Section:</b> 1.2 [intro.refs] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2007-03-08 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#intro.refs">issues</a> in [intro.refs].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -</p> -<blockquote> -<p> -1.2 [intro.refs] Normative references -</p> - -<p> -The following standards contain provisions which, through reference in -this text, constitute provisions of this Interna- tional Standard. At -the time of publication, the editions indicated were valid. All -standards are subject to revision, and parties to agreements based on -this International Standard are encouraged to investigate the -possibility of applying the most recent editions of the standards -indicated below. Members of IEC and ISO maintain registers of currently -valid International Standards. -</p> - -<ul> -<li>Ecma International, ECMAScript Language Specification, Standard -Ecma-262, third edition, 1999.</li> -<li>ISO/IEC 2382 (all parts), Information technology - Vocabulary</li> -<li>ISO/IEC 9899:1990, Programming languages - C</li> -<li>ISO/IEC 9899/Amd.1:1995, Programming languages - C, AMENDMENT 1: C -Integrity</li> -<li>ISO/IEC 9899:1999, Programming languages - C</li> -<li>ISO/IEC 9899:1999/Cor.1:2001 Programming languages - C</li> -<li>ISO/IEC 9899:1999/Cor.2:2004 Programming languages - C</li> -<li>ISO/IEC 9945:2003, Information Technology-Portable Operating System -Interface (POSIX)</li> -<li>ISO/IEC 10646-1:1993 Information technology - Universal Multiple-Octet -Coded Character Set (UCS) - Part 1: Architecture and Basic Multilingual -Plane</li> -</ul> -</blockquote> - -<p> -I'm not sure how many of those reserve naming patterns that might affect -us, but I am equally sure I don't own a copy of any of these to check! -</p> -<p> -The point is to list the reserved naming patterns, rather than the -individual names themselves - although we may want to list C keywords -that are valid identifiers in C++ but likely to cause trouble in shared -headers (e.g. restrict) -</p> - -<p><i>[ -Kona (2007): Recommend NAD. No one has identified a specific defect, just the possibility of one. -]</i></p> - - -<p><i>[ -Post-Kona: Alisdair request Open. A good example of the problem was a -discussion of the system error proposal, where it was pointed out an all-caps -identifier starting with a capital E conflicted with reserved macro names for -both Posix and C. I had absolutely no idea of this rule, and suspect I was -not the only one in the room.<br/> -<br/> -Resolution will require someone with access to all the listed documents to -research their respective name reservation rules, or people with access to -specific documents add their rules to this issue until the list is complete. -]</i></p> - - -<p><i>[ -Bellevue: Wording is aleady present in various standards, and no-one has come forward with wording. -Suggest a formal paper rather than a defect report is the correct way to proceed. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="656"></a>656. Typo in subtract_with_carry_engine declaration</h3> -<p><b>Section:</b> 26.5.2 [rand.synopsis] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-03-08 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.synopsis">issues</a> in [rand.synopsis].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -26.5.2 [rand.synopsis] the header <tt><random></tt> synopsis -contains an unreasonable closing curly brace inside the -<tt>subtract_with_carry_engine</tt> declaration. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change the current declaration in 26.5.2 [rand.synopsis] -</p> - -<blockquote><pre> -template <class UIntType, size_t w<del>}</del>, size_t s, size_t r> -class subtract_with_carry_engine; -</pre></blockquote> - - -<p><i>[ -Pete: Recommends editorial. -]</i></p> - - - - - -<hr> -<h3><a name="657"></a>657. unclear requirement about header inclusion</h3> -<p><b>Section:</b> 17.6.2.2 [using.headers] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Gennaro Prota <b>Opened:</b> 2007-03-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#using.headers">issues</a> in [using.headers].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -17.6.2.2 [using.headers] states: -</p> - -<blockquote><p> -A translation unit shall include a header only outside of any -external declaration or definition, [...] -</p></blockquote> - -<p> -I see three problems with this requirement: -</p> - -<ol style="list-style-type:lower-alpha"> -<li><p>The C++ standard doesn't define what an "external declaration" or -an "external definition" are (incidentally the C99 standard does, and -has a sentence very similar to the above regarding header inclusion). -</p><p> -I think the intent is that the #include directive shall lexically -appear outside *any* declaration; instead, when the issue was pointed -out on comp.std.c++ at least one poster interpreted "external -declaration" as "declaration of an identifier with external linkage". -If this were the correct interpretation, then the two inclusions below -would be legal: -</p> -<blockquote><pre> - // at global scope - static void f() - { -# include <cstddef> - } - - static void g() - { -# include <stddef.h> - } -</pre></blockquote> -<p> -(note that while the first example is unlikely to compile correctly, -the second one may well do) -</p></li> - -<li><p>as the sentence stands, violations will require a diagnostic; is -this the intent? It was pointed out on comp.std.c++ (by several -posters) that at least one way to ensure a diagnostic exists: -</p> -<blockquote><p> - [If there is an actual file for each header,] one simple way - to implement this would be to insert a reserved identifier - such as __begin_header at the start of each standard header. - This reserved identifier would be ignored for all other - purposes, except that, at the appropriate point in phase 7, if - it is found inside an external definition, a diagnostic is - generated. There's many other similar ways to achieve the same - effect. - </p> -<p> --James Kuyper, on comp.std.c++ -</p></blockquote></li> - -<li><p>is the term "header" meant to be limited to standard headers? -Clause 17 is all about the library, but still the general question is -interesting and affects one of the points in the explicit namespaces -proposal (<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1691.html">n1691</a>): -</p> -<blockquote><p> - Those seeking to conveniently enable argument-dependent - lookups for all operators within an explicit namespace - could easily create a header file that does so: -</p><pre> - namespace mymath:: - { - #include "using_ops.hpp" - } -</pre></blockquote> -</li> -</ol> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p><p> -We believe that the existing language does not cause any real confusion -and any new formulation of the rules that we could come up with are -unlikely to be better than what's already in the standard. -</p> - - - - -<hr> -<h3><a name="662"></a>662. Inconsistent handling of incorrectly-placed thousands separators</h3> -<p><b>Section:</b> 22.4.2.1.2 [facet.num.get.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Cosmin Truta <b>Opened:</b> 2007-04-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#facet.num.get.virtuals">active issues</a> in [facet.num.get.virtuals].</p> -<p><b>View all other</b> <a href="lwg-index.html#facet.num.get.virtuals">issues</a> in [facet.num.get.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -From Section 22.4.2.1.2 [facet.num.get.virtuals], paragraphs 11 and 12, it is implied -that the value read from a stream must be stored -even if the placement of thousands separators does not conform to the -<code>grouping()</code> specification from the <code>numpunct</code> facet. -Since incorrectly-placed thousands separators are flagged as an extraction -failure (by the means of <code>failbit</code>), we believe it is better not -to store the value. A consistent strategy, in which any kind of extraction -failure leaves the input item intact, is conceptually cleaner, is able to avoid -corner-case traps, and is also more understandable from the programmer's point -of view. -</p> -<p> -Here is a quote from <i>"The C++ Programming Language (Special Edition)"</i> -by B. Stroustrup (Section D.4.2.3, pg. 897): -</p> -<blockquote><p> -<i>"If a value of the desired type could not be read, failbit is set in r. -[...] An input operator will use r to determine how to set the state of its -stream. If no error was encountered, the value read is assigned through v; -otherwise, v is left unchanged."</i> -</p></blockquote> -<p> -This statement implies that <code>rdstate()</code> alone is sufficient to -determine whether an extracted value is to be assigned to the input item -<i>val</i> passed to <code>do_get</code>. However, this is in disagreement -with the current C++ Standard. The above-mentioned assumption is true in all -cases, except when there are mismatches in digit grouping. In the latter case, -the parsed value is assigned to <i>val</i>, and, at the same time, <i>err</i> -is assigned to <code>ios_base::failbit</code> (essentially "lying" about the -success of the operation). Is this intentional? The current behavior raises -both consistency and usability concerns. -</p> -<p> -Although digit grouping is outside the scope of <code>scanf</code> (on which -the virtual methods of <code>num_get</code> are based), handling of grouping -should be consistent with the overall behavior of scanf. The specification of -<code>scanf</code> makes a distinction between input failures and matching -failures, and yet both kinds of failures have no effect on the input items -passed to <code>scanf</code>. A mismatch in digit grouping logically falls in -the category of matching failures, and it would be more consistent, and less -surprising to the user, to leave the input item intact whenever a failure is -being signaled. -</p> -<p> -The extraction of <code>bool</code> is another example outside the scope of -<code>scanf</code>, and yet consistent, even in the event of a successful -extraction of a <code>long</code> but a failed conversion from -<code>long</code> to <code>bool</code>. -</p> -<p> -Inconsistency is further aggravated by the fact that, when failbit is set, -subsequent extraction operations are no-ops until <code>failbit</code> is -explicitly cleared. Assuming that there is no explicit handling of -<code>rdstate()</code> (as in <code>cin>>i>>j</code>) it is -counter-intuitive to be able to extract an integer with mismatched digit -grouping, but to be unable to extract another, properly-formatted integer -that immediately follows. -</p> -<p> -Moreover, setting <code>failbit</code>, and selectively assigning a value to -the input item, raises usability problems. Either the strategy of -<code>scanf</code> (when there is no extracted value in case of failure), or -the strategy of the <code>strtol</code> family (when there is always an -extracted value, and there are well-defined defaults in case of a failure) are -easy to understand and easy to use. On the other hand, if <code>failbit</code> -alone cannot consistently make a difference between a failed extraction, and a -successful but not-quite-correct extraction whose output happens to be the same -as the previous value, the programmer must resort to implementation tricks. -Consider the following example: -</p> -<pre> - int i = old_i; - cin >> i; - if (cin.fail()) - // can the value of i be trusted? - // what does it mean if i == old_i? - // ... -</pre> -<p> -Last but not least, the current behvaior is not only confusing to the casual -reader, but it has also been confusing to some book authors. Besides -Stroustrup's book, other books (e.g. "Standard C++ IOStreams and Locales" by -Langer and Kreft) are describing the same mistaken assumption. Although books -are not to be used instead of the standard reference, the readers of these -books, as well as the people who are generally familiar to <code>scanf</code>, -are even more likely to misinterpret the standard, and expect the input items -to remain intact when a failure occurs. -</p> - - -<p><b>Proposed resolution:</b></p> - -<p> -Change 22.4.2.1.2 [facet.num.get.virtuals]: -</p> - -<blockquote> -<p> -<b>Stage 3:</b> The result of stage 2 processing can be one of -</p> -<ul> -<li>A sequence of <code>chars</code> has been accumulated in stage 2 that is converted (according to the rules of <code>scanf</code>) to a value of the type of <code><i>val</i></code>. <del>This value is stored in <code><i>val</i></code> and <code>ios_base::goodbit</code> is stored in <code><i>err</i></code>.</del></li> - -<li>The sequence of <code>chars</code> accumulated in stage 2 would have caused <code>scanf</code> to report an input failure. <code>ios_base::failbit</code> is assigned to <code><i>err</i></code>.</li> -</ul> -<p> -<ins>In the first case,</ins> <del>D</del><ins>d</ins>igit grouping is checked. That is, the positions of discarded separators is examined for consistency with <code>use_facet<numpunct<charT> >(<i>loc</i>).grouping()</code>. If they are not consistent then <code>ios_base::failbit</code> is assigned to <code><i>err</i></code>. <ins>Otherwise, the value that was converted in stage 2 is stored in <code><i>val</i></code> and <code>ios_base::goodbit</code> is stored in <code><i>err</i></code>.</ins> -</p> -</blockquote> - - -<p><b>Rationale:</b></p><p> -post-Toronto: Changed from New to NAD at the request of the author. The preferred solution of -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2327.pdf">N2327</a> -makes this resolution obsolete. -</p> - - - - -<hr> -<h3><a name="663"></a>663. Complexity Requirements</h3> -<p><b>Section:</b> 17.5.1.4 [structure.specifications] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thomas Plum <b>Opened:</b> 2007-04-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#structure.specifications">issues</a> in [structure.specifications].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -17.5.1.4 [structure.specifications] para 5 says -</p> - -<blockquote><p> --5- Complexity requirements specified in the library -clauses are upper bounds, and implementations that provide better -complexity guarantees satisfy the requirements. -</p></blockquote> - -<p> -The following -objection has been raised: -</p> - -<blockquote><p> -The library clauses suggest general -guidelines regarding complexity, but we have been unable to discover -any absolute hard-and-fast formulae for these requirements. Unless -or until the Library group standardizes specific hard-and-fast -formulae, we regard all the complexity requirements as subject to a -"fudge factor" without any intrinsic upper bound. -</p></blockquote> - -<p> -[Plum ref -_23213Y31 etc] -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p><p> -Kona (2007): No specific instances of underspecification have been -identified, and big-O notation always involves constant factors. -</p> - - - - -<hr> -<h3><a name="667"></a>667. <tt>money_get</tt>'s widened minus sign</h3> -<p><b>Section:</b> 22.4.6.1.2 [locale.money.get.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thomas Plum <b>Opened:</b> 2007-04-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.money.get.virtuals">issues</a> in [locale.money.get.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -22.4.6.1.2 [locale.money.get.virtuals], para 1 says: -</p> - -<blockquote><p> -The result is returned as an integral value -stored in <tt>units</tt> or as a sequence of digits possibly preceded by a -minus sign (as produced by <tt>ct.widen(c)</tt> where <tt>c</tt> is '-' or in the range -from '0' through '9', inclusive) stored in <tt>digits</tt>. -</p></blockquote> - -<p> -The following -objection has been raised: -</p> - -<blockquote><p> -Some implementations interpret this to mean that a facet derived from -<tt>ctype<wchar_t></tt> can provide its own member <tt>do_widen(char)</tt> -which produces e.g. <tt>L'@'</tt> for the "widened" minus sign, and that the -<tt>'@'</tt> symbol will appear in the resulting sequence of digits. Other -implementations have assumed that one or more places in the standard permit the -implementation to "hard-wire" <tt>L'-'</tt> as the "widened" minus sign. Are -both interpretations permissible, or only one? -</p></blockquote> - -<p> -[Plum ref _222612Y14] -</p> - -<p> -Furthermore: if <tt>ct.widen('9')</tt> produces <tt>L'X'</tt> (a non-digit), does a -parse fail if a <tt>'9'</tt> appears in the subject string? [Plum ref _22263Y33] -</p> - -<p><i>[ -Kona (2007): Bill and Dietmar to provide proposed wording. -]</i></p> - - -<p><i>[ -post Bellevue: Bill adds: -]</i></p> - - -<blockquote><p> -The Standard is clear that the minus sign stored in <tt>digits</tt> is <tt>ct.widen('-')</tt>. -The subject string must contain characters <tt>c</tt> in the set <tt>[-0123456789]</tt> -which are translated by <tt>ct.widen(c)</tt> calls before being stored in <tt>digits</tt>; -the widened characters are not relevant to the parsing of the subject string. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with Bill's comment above, -in line with the first of the interpretations offered in the issue. -Move to NAD. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="668"></a>668. <tt>money_get</tt>'s empty minus sign</h3> -<p><b>Section:</b> 22.4.6.1.2 [locale.money.get.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thomas Plum <b>Opened:</b> 2007-04-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.money.get.virtuals">issues</a> in [locale.money.get.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -22.4.6.1.2 [locale.money.get.virtuals], para 3 says: -</p> - -<blockquote><p> -If <tt>pos</tt> or <tt>neg</tt> is empty, the sign component is -optional, and if no sign is detected, the result is given the sign -that corresponds to the source of the empty string. -</p></blockquote> - -<p> -The following objection has been raised: -</p> - -<blockquote><p> -A <tt>negative_sign</tt> of "" means "there is no -way to write a negative sign" not "any null sequence is a negative -sign, so it's always there when you look for it". -</p></blockquote> - -<p> -[Plum ref _222612Y32] -</p> - -<p><i>[ -Kona (2007): Bill to provide proposed wording and interpretation of existing wording. -]</i></p> - - -<p> -Related to <a href="lwg-closed.html#669">669</a>. -</p> - -<p><i>[ -2009-05-17 Howard adds: -]</i></p> - - -<blockquote> -<p> -I disagree that a <tt>negative_sign</tt> of "" means "there is no way to -write a negative sign". The meaning requires the sentences of 22.4.6.1.2 [locale.money.get.virtuals] p3 following that quoted above to be -taken into account: -</p> - -<blockquote><p> --3- ... If <tt>pos</tt> or <tt>neg</tt> is empty, the sign component is -optional, and if no sign is detected, the result is given the sign that -corresponds to the source of the empty string. Otherwise, the character -in the indicated position must match the first character of <tt>pos</tt> -or <tt>neg</tt>, and the result is given the corresponding sign. If the -first character of <tt>pos</tt> is equal to the first character of -<tt>neg</tt>, or if both strings are empty, the result is given a -positive sign. -</p></blockquote> - -<p> -So a <tt>negative_sign</tt> of "" means "there is no way to write a -negative sign" only when <tt>positive_sign</tt> is also "". However -when <tt>negative_sign</tt> is "" and <tt>postive_sign.size() > -0</tt>, then one writes a negative value by not writing the -<tt>postive_sign</tt> in the position indicated by -<tt>money_base::sign</tt>. -For example: -</p> - -<blockquote><pre> -pattern = {symbol, sign, value, none} -positive_sign = "+" -negative_sign = "" -$123 // a negative value, using optional sign -$+123 // a positive value -$-123 // a parse error -</pre></blockquote> - -<p> -And: -</p> - -<blockquote><pre> -pattern = {symbol, sign, value, none} -positive_sign = "" -negative_sign = "" -$123 // a positive value, no sign possible -$+123 // a parse error -$-123 // a parse error -</pre></blockquote> - - -<p> -And (regarding <a href="lwg-closed.html#669">669</a>): -</p> - -<blockquote><pre> -pattern = {symbol, sign, value, none} -positive_sign = "-" -negative_sign = "-" -$123 // a parse error, sign is mandatory -$+123 // a parse error -$-123 // a positive value -</pre></blockquote> - - -<p> -The text seems both unambiguous and clear to me. I recommend NAD for -both this issue and <a href="lwg-closed.html#669">669</a>. However I would have no -objection to adding examples such as those above. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -This discussion applies equally to issue <a href="lwg-closed.html#669">669</a> (q.v.). -Howard has added examples above, -and recommends either NAD or a resolution that adds his (or similar) examples -to the Working Paper. -</p> -<p> -Alan would like to rewrite paragraph 3. -</p> -<p> -We recommend moving to NAD. -Anyone who feels strongly about adding the examples -is invited to submit corresponding wording. -We further recommend issue <a href="lwg-closed.html#669">669</a> be handled identically. -</p> -</blockquote> - -<p><i>[ -2009-07-14 Alan reopens with improved wording. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -No consensus for closing as NAD. Leave in Review. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -NAD. Agreed that the original assessment as NAD was correct. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 22.4.6.1.2 [locale.money.get.virtuals] p3: -</p> - -<blockquote><p> --3- <del>If the first character (if any) in the string pos returned by -<tt>mp.positive_sign()</tt> or the string <tt>neg</tt> returned by -<tt>mp.negative_sign()</tt> is recognized in the position indicated by -sign in the format pattern, it is consumed and any remaining characters -in the string are required after all the other format components. -[<i>Example:</i> If <tt>showbase</tt> is off, then for a <tt>neg</tt> -value of "()" and a currency symbol of "L", in "(100 L)" the "L" is -consumed; but if <tt>neg</tt> is "-", the "L" in "-100 L" is not -consumed. -- <i>end example</i>] If <tt>pos</tt> or <tt>neg</tt> is -empty, the sign component is optional, and if no sign is detected, the -result is given the sign that corresponds to the source of the empty -string. Otherwise, the character in the indicated position must match -the first character of <tt>pos</tt> or <tt>neg</tt>, and the result is -given the corresponding sign. If the first character of <tt>pos</tt> is -equal to the first character of <tt>neg</tt>, or if both strings are -empty, the result is given a positive sign.</del> - -<ins>The sign pattern strings <tt>pos</tt> and <tt>neg</tt> are returned by -<tt>mp.positive_sign()</tt> and <tt>mp.negative_sign()</tt> respectively. A sign pattern -is matched if its first character is recognized in <tt>s</tt> in the position -indicated by <tt>sign</tt> in the format pattern, or if the pattern is empty and -there is no sign recognized in <tt>s</tt>. A match is required to occur. If both -patterns are matched, the result is given a positive sign, otherwise the -result is given the sign corresponding to the matched pattern. -If the pattern contains more than one character, the characters after the first -must be matched in <tt>s</tt> after all other format components. -If any sign -characters are matched, <tt>s</tt> is consumed up to and including those characters. -[<i>Example:</i> If <tt>showbase</tt> is off, then for a <tt>neg</tt> -value of "<tt>()</tt>" and a currency symbol of "<tt>L</tt>", in -"<tt>(100 L)</tt>" the entire string is consumed; but for a <tt>neg</tt> -value of "<tt>-</tt>", in "<tt>-100 L</tt>", the string is consumed -through the second "<tt>0</tt>" (the space and "<tt>L</tt>" are not consumed). — <i>end -example</i>] </ins> -</p></blockquote> - - - - - -<hr> -<h3><a name="669"></a>669. Equivalent postive and negative signs in <tt>money_get</tt></h3> -<p><b>Section:</b> 22.4.6.1.2 [locale.money.get.virtuals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thomas Plum <b>Opened:</b> 2007-04-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#locale.money.get.virtuals">issues</a> in [locale.money.get.virtuals].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -22.4.6.1.2 [locale.money.get.virtuals], para 3 sentence 4 says: -</p> - -<blockquote><p> -If the first character of <tt>pos</tt> is equal to the first character of <tt>neg</tt>, -or if both strings are empty, the result is given a positive sign. -</p></blockquote> - -<p> -One interpretation is that an input sequence must match either the -positive pattern or the negative pattern, and then in either event it -is interpreted as positive. The following objections has been raised: -</p> - -<blockquote><p> -The input can successfully match only a positive sign, so the negative -pattern is an unsuccessful match. -</p></blockquote> - -<p> -[Plum ref _222612Y34, 222612Y51b] -</p> - -<p><i>[ -Bill to provide proposed wording and interpretation of existing wording. -]</i></p> - - -<p><i>[ -2009-05-17 See Howard's comments in related issue <a href="lwg-closed.html#668">668</a>. -]</i></p> - - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -This discussion applies equally to issue <a href="lwg-closed.html#668">668</a> (q.v.). -Howard has added examples there, -and recommends either NAD or a resolution that adds his (or similar) examples -to the Working Paper. -</p> -<p> -We recommend moving to NAD. -Anyone who feels strongly about adding the examples -is invited to submit corresponding wording. -We further recommend issue <a href="lwg-closed.html#668">668</a> be handled identically. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="670"></a>670. <tt>money_base::pattern</tt> and <tt>space</tt></h3> -<p><b>Section:</b> 22.4.6.3 [locale.moneypunct] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Thomas Plum <b>Opened:</b> 2007-04-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#836">836</a></p> -<p><b>Discussion:</b></p> -<p> -22.4.6.3 [locale.moneypunct], para 2 says: -</p> - -<blockquote><p> -The value <tt>space</tt> indicates that at least one space is required at -that position. -</p></blockquote> - -<p> -The following objection has been raised: -</p> - -<blockquote><p> -Whitespace is optional when matching space. (See 22.4.6.1.2 [locale.money.get.virtuals], para 2.) -</p></blockquote> - -<p> -[Plum ref _22263Y22] -</p> - -<p><i>[ -Kona (2007): Bill to provide proposed wording. We agree that C++03 is -ambiguous, and that we want C++0X to say "space" means 0 or more -whitespace characters on input. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="683"></a>683. regex_token_iterator summary error</h3> -<p><b>Section:</b> 28.12.2 [re.tokiter] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Eric Niebler <b>Opened:</b> 2007-06-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#re.tokiter">issues</a> in [re.tokiter].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -28.12.2 [re.tokiter], p3 says: -</p> -<blockquote> -<p> -After it is constructed, the iterator finds and stores a value -<tt>match_results<BidirectionalIterator></tt> position and sets the -internal count <tt>N</tt> to zero. -</p> -</blockquote> - -<p> -Should read: -</p> - -<blockquote> -<p> -After it is constructed, the iterator finds and stores a value -<tt><del>match_results</del><ins>regex_iterator</ins><BidirectionalIterator<ins>, charT, traits</ins>></tt> -position and sets the internal count <tt>N</tt> to zero. -</p> -</blockquote> - -<p><i>[ -John adds: -]</i></p> - - -<blockquote><p> -Yep, looks like a typo/administrative fix to me. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="684"></a>684. Unclear which members of match_results should be used in comparison</h3> -<p><b>Section:</b> 28.10 [re.results] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Nozomu Katoo <b>Opened:</b> 2007-05-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#re.results">issues</a> in [re.results].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In 28.4 [re.syn] of N2284, two template functions -are declared here: -</p> -<blockquote><pre> -// 28.10, class template match_results: - <<i>snip</i>> -// match_results comparisons - template <class BidirectionalIterator, class Allocator> - bool operator== (const match_results<BidirectionalIterator, Allocator>& m1, - const match_results<BidirectionalIterator, Allocator>& m2); - template <class BidirectionalIterator, class Allocator> - bool operator!= (const match_results<BidirectionalIterator, Allocator>& m1, - const match_results<BidirectionalIterator, Allocator>& m2); - -// 28.10.6, match_results swap: -</pre></blockquote> - -<p> -But the details of these two bool operator functions (i.e., which members of -<tt>match_results</tt> should be used in comparison) are not described in any -following sections. -</p> - -<p><i>[ -John adds: -]</i></p> - - -<blockquote><p> -That looks like a bug: <tt>operator==</tt> should return <tt>true</tt> only if -the two objects refer to the same match - ie if one object was constructed as a -copy of the other. -</p></blockquote> - -<p><i>[ -Kona (2007): Bill and Pete to add minor wording to that proposed in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2409.pdf">N2409</a>. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add a new section after 28.10.7 [re.results.swap], which reads: -</p> -<p> -28.10.7 match_results non-member functions. -</p> - -<blockquote> -<pre> -template<class BidirectionalIterator, class Allocator> - bool operator==(const match_results<BidirectionalIterator, Allocator>& m1, - const match_results<BidirectionalIterator, Allocator>& m2); -</pre> -<blockquote> -<p> -<i>Returns:</i> <tt>true</tt> only if the two objects refer to the same match. -</p> -</blockquote> -</blockquote> - -<blockquote> -<pre> -template<class BidirectionalIterator, class Allocator> - bool operator!=(const match_results<BidirectionalIterator, Allocator>& m1, - const match_results<BidirectionalIterator, Allocator>& m2); -</pre> -<blockquote> -<p> -<i>Returns:</i> <tt>!(m1 == m2)</tt>. -</p> -</blockquote> -</blockquote> - -<blockquote> -<pre> -template<class BidirectionalIterator, class Allocator> - void swap(match_results<BidirectionalIterator, Allocator>& m1, - match_results<BidirectionalIterator, Allocator>& m2); -</pre> -<blockquote> -<p> -<i>Returns:</i> <tt>m1.swap(m2)</tt>. -</p> -</blockquote> -</blockquote> - - -<p><i>[ -Bellevue: Proposed wording now in WP. -]</i></p> - - - - - -<hr> -<h3><a name="686"></a>686. <tt>unique_ptr</tt> and <tt>shared_ptr</tt> fail to specify non-convertibility to int for unspecified-bool-type</h3> -<p><b>Section:</b> 20.8.1.2.4 [unique.ptr.single.observers], 20.8.2.2.5 [util.smartptr.shared.obs] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2007-06-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The standard library uses the <tt>operator <i>unspecified-bool-type</i>() const</tt> idiom in -five places. In three of those places (20.9.12.2.3 [func.wrap.func.cap], function capacity -for example) the returned value is constrained to disallow -unintended conversions to int. The standardese is -</p> -<blockquote><p> -The return type shall not be convertible to <tt>int</tt>. -</p></blockquote> -<p> -This constraint is omitted for <tt>unique_ptr</tt> and <tt>shared_ptr</tt>. It should be added for those. -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Close as NAD. Accepting paper -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2435.htm">N2435</a> -makes it irrelevant. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -To the <i>Returns</i> paragraph for <tt>operator <i>unspecified-bool-type</i>() -const</tt> of 20.8.1.2.4 [unique.ptr.single.observers] paragraph 11 and 20.8.2.2.5 [util.smartptr.shared.obs] paragraph 16, add the sentence: -</p> -<blockquote><p> -The return type shall not be convertible to <tt>int</tt>. -</p></blockquote> - - -<p><i>[ -Kona (2007): Uncertain if <tt>nullptr</tt> will address this issue. -]</i></p> - - - - - -<hr> -<h3><a name="690"></a>690. abs(long long) should return long long</h3> -<p><b>Section:</b> 26.8 [c.math] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Niels Dekker <b>Opened:</b> 2007-06-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.math">active issues</a> in [c.math].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Quoting the latest draft (n2135), 26.8 [c.math]: -</p> - -<blockquote> -<p> -The added signatures are: -</p> -<blockquote><pre> -long abs(long); // labs() -long abs(long long); // llabs() -</pre></blockquote> -</blockquote> -<p> -Shouldn't <tt>abs(long long)</tt> have <tt>long long</tt> as return type? -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 26.8 [c.math]: -</p> -<blockquote><pre> -<ins>long </ins>long abs(long long); // llabs() -</pre></blockquote> - - -<p><b>Rationale:</b></p><p> -Had already been fixed in the WP by the time the LWG reviewed this. -</p> - - - - -<hr> -<h3><a name="701"></a>701. assoc laguerre poly's</h3> -<p><b>Section:</b> TR1 5.2.1.1 [tr.num.sf.Lnm] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Christopher Crawford <b>Opened:</b> 2007-06-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I see that the definition the associated Laguerre -polynomials TR1 5.2.1.1 [tr.num.sf.Lnm] has been corrected since -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2004/n1687.pdf">N1687</a>. -However, the draft standard only specifies ranks of integer value <tt>m</tt>, -while the associated Laguerre polynomials are actually valid for real -values of <tt>m > -1</tt>. In the case of non-integer values of <tt>m</tt>, the -definition <tt><i>L</i><sub>n</sub><sup>(m)</sup> = (1/n!)e<sup>x</sup>x<sup>-m</sup> (d/dx)<sup>n</sup> (e<sup>-x</sup>x<sup>m+n</sup>)</tt> -must be used, which also holds for integer values of <tt>m</tt>. See -Abramowitz & Stegun, 22.11.6 for the general case, and 22.5.16-17 for -the integer case. In fact fractional values are most commonly used in -physics, for example to <tt>m = +/- 1/2</tt> to describe the harmonic -oscillator in 1 dimension, and <tt>1/2, 3/2, 5/2, ...</tt> in 3 -dimensions. -</p> -<p> -If I am correct, the calculation of the more general case is no -more difficult, and is in fact the function implemented in the GNU -Scientific Library. I would urge you to consider upgrading the -standard, either adding extra functions for real <tt>m</tt> or switching the -current ones to <tt>double</tt>. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We understand the issue, and have opted not to extend as recommended. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="702"></a>702. Restriction in associated Legendre functions</h3> -<p><b>Section:</b> TR1 5.2.1.2 [tr.num.sf.Plm] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Christopher Crawford <b>Opened:</b> 2007-06-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -One other small thing, in TR1 5.2.1.2 [tr.num.sf.Plm], the restriction should be -<tt>|x| <= 1</tt>, not <tt>x >= 0</tt>.</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -The error has been corrected in the pending IS. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="707"></a>707. null pointer constant for <tt>exception_ptr</tt></h3> -<p><b>Section:</b> 18.8.5 [propagation] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Jens Maurer <b>Opened:</b> 2007-07-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#propagation">issues</a> in [propagation].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -From the Toronto Core wiki: -</p> - -<p> -What do you mean by "null pointer constant"? How do you guarantee that -<tt>exception_ptr() == 1</tt> doesn't work? Do you even want to prevent that? -What's the semantics? What about <tt>void *p = 0; exception_ptr() == p</tt>? -Maybe disallow those in the interface, but how do you do that with -portable C++? Could specify just "make it work". -</p> - -<p> -Peter's response: -</p> - -<p> -null pointer constant as defined in 4.10 [conv.ptr]. Intent is "just make it -work", can be implemented as assignment operator taking a unique pointer -to member, as in the unspecified bool type idiom. -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote> -<p> -Original implementation was possible using the "unspecified-null-pointer" idiom, similar to unspecified-bool. -</p> -<p> -Even simpler now with nullptr_t. -</p> -<p> -NAD Rationale : null pointer constant is a perfectly defined term, and -while API is clearly implementable there is no need to spell out -implementation details. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="717"></a>717. Incomplete <tt>valarray::operator[]</tt> specification in [valarray.access]</h3> -<p><b>Section:</b> 26.6.2.4 [valarray.access] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-08-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#valarray.access">issues</a> in [valarray.access].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Since the return type of <tt>valarray</tt>'s <tt>operator[] const</tt> overload has been -changed to <tt>const T&</tt> as described in <a href="lwg-defects.html#389">389</a> several paragraphs of -the section 26.6.2.4 [valarray.access] are now -incompletely -specified, because many requirements and guarantees should now also -apply to the const overload. Most notably, the address and reference -guarantees should be extended to the const overload case. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 26.6.2.4 [valarray.access]: -</p> - -<blockquote> -<p> --1- <del>When applied to a constant array, the subscript operator returns a -reference to the corresponding element of the array. When applied to a -non-constant array, t</del><ins>T</ins>he subscript operator returns a -reference to the corresponding element of the array. -</p> - -<p> --3- The expression <tt>&a[i+j] == &a[i] + j</tt> evaluates as <tt>true</tt> for all <tt>size_t i</tt> -and <tt>size_t j</tt> such that <tt>i+j</tt> is less -than the length of the <del>non-constant</del> array <tt>a</tt>. -</p> - -<p> --4- Likewise, the expression <tt>&a[i] != &b[j]</tt> evaluates -as <tt>true</tt> for any two <del>non-constant</del> arrays <tt>a</tt> and -<tt>b</tt> and for any <tt>size_t i</tt> and <tt>size_t j</tt> such that -<tt>i</tt> is less than the length of <tt>a</tt> and <tt>j</tt> is less -than the length of <tt>b</tt>. This property indicates an absence of -aliasing and may be used to advantage by optimizing -compilers.<sup>281)</sup> -</p> - -<p> --5- The reference returned by the subscript operator for a<ins>n</ins> <del>non-constant</del> array is guaranteed to be valid until -the member function <tt>resize(size_t, T)</tt> (26.5.2.7) is called for that array or until the lifetime -of that array ends, whichever happens first. -</p> - -</blockquote> - - - - - - -<hr> -<h3><a name="718"></a>718. <tt>basic_string</tt> is not a sequence</h3> -<p><b>Section:</b> 21.4 [basic.string] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Bo Persson <b>Opened:</b> 2007-08-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#basic.string">active issues</a> in [basic.string].</p> -<p><b>View all other</b> <a href="lwg-index.html#basic.string">issues</a> in [basic.string].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Paragraph 21.4 [basic.string]/3 states: -</p> - -<blockquote> -<p> -The class template <tt>basic_string</tt> conforms to the requirements for a -Sequence (23.1.1) and for a Reversible Container (23.1). -</p> -</blockquote> - -<p> -First of all, 23.2.3 [sequence.reqmts] is no longer "Sequence" but "Sequence container". -Secondly, after the resent changes to containers (<tt>emplace</tt>, <tt>push_back</tt>, -<tt>const_iterator</tt> parameters to <tt>insert</tt> and <tt>erase</tt>), <tt>basic_string</tt> is not -even close to conform to the current requirements. -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote> -<ul> -<li>emplace, for example, may not make sense for strings. Is also likely suboptimal</li> -<li>with concepts do we need to maintain string as sequence container?</li> -<li>One approach might be to say something like: string is a sequence except it doesn't have these functions</li> -</ul> -<ul> -<li>basic_string already has push_back</li> -<li>const_iterator parameters to insert and erase should be added to basic_string</li> -<li>this leaves emplace to handle -- we have the following options: -<ul> -<li>option 1: add it to string even though it's optional</li> -<li>option 2: make emplace optional to sequences (move from table 89 to 90)</li> -<li>option 3: say string not sequence (the proposal),</li> -<li>option 4: add an exception to basic string wording.</li> -</ul> -</li> -</ul> -<p>General consensus is to suggest option 2.</p> -</blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Move to NAD Editorial -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Remove this sentence, in recognition of the fact that <tt>basic_string</tt> is -not just a <tt>vector</tt>-light for literal types, but something quite -different, a string abstraction in its own right. -</p> - - - - - -<hr> -<h3><a name="721"></a>721. <tt>wstring_convert</tt> inconsistensies</h3> -<p><b>Section:</b> 22.3.3.2.2 [conversions.string] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Bo Persson <b>Opened:</b> 2007-08-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#conversions.string">active issues</a> in [conversions.string].</p> -<p><b>View all other</b> <a href="lwg-index.html#conversions.string">issues</a> in [conversions.string].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Paragraph 3 says that the <tt>Codecvt</tt> template parameter shall meet the -requirements of <tt>std::codecvt</tt>, even though <tt>std::codecvt</tt> itself cannot -be used (because of a protected destructor). -</p> - -<p> -How are we going to explain this code to beginning programmers? -</p> - -<blockquote><pre> -template<class I, class E, class S> -struct codecvt : std::codecvt<I, E, S> -{ - ~codecvt() - { } -}; - -void main() -{ - std::wstring_convert<codecvt<wchar_t, char, std::mbstate_t> > compiles_ok; - - std::wstring_convert<std::codecvt<wchar_t, char, std::mbstate_t> > not_ok; -} -</pre></blockquote> - -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote><p> -Bill will propose a resolution. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote> -<p> -codecvt isn't intended for beginning programmers. This is a regrettable -consequence of the original design of the facet. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="725"></a>725. Optional sequence container requirements column label</h3> -<p><b>Section:</b> 23.2.3 [sequence.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2007-09-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#sequence.reqmts">issues</a> in [sequence.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Table 90: (Optional sequence container operations) states the -"assertion note pre/post-condition" of <tt>operator[]</tt> to be -</p> - -<blockquote><pre> -*(a.begin() + n) -</pre></blockquote> - -<p> -Surely that's meant to be "operational semantics?" -</p> - - - -<p><b>Proposed resolution:</b></p> -<blockquote> -<table border="1"> -<caption>Table 90: Optional sequence container operations</caption> -<tr> -<th>expression</th> <th>return type</th> <th><del>assertion/note<br/>pre/post-condition</del><br/> <ins>operational semantics</ins></th> <th>container</th> -</tr> -</table> -</blockquote> - - - - - - -<hr> -<h3><a name="726"></a>726. Missing <tt>regex_replace()</tt> overloads</h3> -<p><b>Section:</b> 28.11.4 [re.alg.replace] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2007-09-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#re.alg.replace">issues</a> in [re.alg.replace].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Two overloads of <tt>regex_replace()</tt> are currently provided: -</p> - -<blockquote><pre> -template <class OutputIterator, class BidirectionalIterator, - class traits, class charT> - OutputIterator - regex_replace(OutputIterator out, - BidirectionalIterator first, BidirectionalIterator last, - const basic_regex<charT, traits>& e, - const basic_string<charT>& fmt, - regex_constants::match_flag_type flags = - regex_constants::match_default); - -template <class traits, class charT> - basic_string<charT> - regex_replace(const basic_string<charT>& s, - const basic_regex<charT, traits>& e, - const basic_string<charT>& fmt, - regex_constants::match_flag_type flags = - regex_constants::match_default); -</pre></blockquote> - -<ol> -<li>Overloads taking <tt>const charT *</tt> are provided for <tt>regex_match()</tt> and -<tt>regex_search()</tt>, but not <tt>regex_replace()</tt>. This is inconsistent.</li> -<li> -<p>The absence of <tt>const charT *</tt> overloads prevents ordinary-looking code from compiling, such as:</p> - -<blockquote><pre> -const string s("kitten"); -const regex r("en"); -cout << regex_replace(s, r, "y") << endl; -</pre></blockquote> - -<p> -The compiler error message will be something like "could not deduce -template argument for 'const std::basic_string<_Elem> &' from 'const -char[1]'". -</p> - -<p> -Users expect that anything taking a <tt>basic_string<charT></tt> can also take a -<tt>const charT *</tt>. In their own code, when they write a function taking -<tt>std::string</tt> (or <tt>std::wstring</tt>), they can pass a <tt>const char *</tt> (or <tt>const -wchar_t *</tt>), thanks to <tt>basic_string</tt>'s implicit constructor. Because the -regex algorithms are templated on <tt>charT</tt>, they can't rely on -<tt>basic_string</tt>'s implicit constructor (as the compiler error message -indicates, template argument deduction fails first). -</p> - -<p> -If a user figures out what the compiler error message means, workarounds -are available - but they are all verbose. Explicit template arguments -could be given to <tt>regex_replace()</tt>, allowing <tt>basic_string</tt>'s implicit -constructor to be invoked - but <tt>charT</tt> is the last template argument, not -the first, so this would be extremely verbose. Therefore, constructing -a <tt>basic_string</tt> from each C string is the simplest workaround. -</p> -</li> - -<li> -There is an efficiency consideration: constructing <tt>basic_string</tt>s can -impose performance costs that could be avoided by a library -implementation taking C strings and dealing with them directly. -(Currently, for replacement sources, C strings can be converted into -iterator pairs at the cost of verbosity, but for format strings, there -is no way to avoid constructing a <tt>basic_string</tt>.) -</li> -</ol> - -<p><i>[ -Sophia Antipolis: -]</i></p> - - -<blockquote><p> -We note that Boost already has these overloads. However, the proposed -wording is provided only for 28.11.4 [re.alg.replace]; wording is needed for the synopsis -as well. We also note that this has impact on <tt>match_results::format</tt>, -which may require further overloads. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Daniel to tweak for us. -</p></blockquote> - -<p><i>[ -2009-07-25 Daniel tweaks both this issue and <a href="lwg-defects.html#727">727</a>. -]</i></p> - - -<blockquote> -<p> -This is solved by the proposed resolution of <a href="lwg-defects.html#727">727</a>. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Leave Open. Though we believe this is solved by the proposed resolution -to <a href="lwg-defects.html#727">727</a>. -</p></blockquote> - -<p><i>[ -2010-01-27 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - -<p><b>Rationale:</b></p> -<p> -Solved by <a href="lwg-defects.html#727">727</a>. -</p> - - -<p><b>Proposed resolution:</b></p> - -<p> -Provide additional overloads for <tt>regex_replace()</tt>: one additional -overload of the iterator-based form (taking <tt>const charT* fmt</tt>), and three -additional overloads of the convenience form (one taking <tt>const charT* -str</tt>, another taking <tt>const charT* fmt</tt>, and the third taking both <tt>const -charT* str</tt> and <tt>const charT* fmt</tt>). 28.11.4 [re.alg.replace]: -</p> - -<blockquote> -<pre> -template <class OutputIterator, class BidirectionalIterator, - class traits, class charT> - OutputIterator - regex_replace(OutputIterator out, - BidirectionalIterator first, BidirectionalIterator last, - const basic_regex<charT, traits>& e, - const basic_string<charT>& fmt, - regex_constants::match_flag_type flags = - regex_constants::match_default); - -<ins>template <class OutputIterator, class BidirectionalIterator, - class traits, class charT> - OutputIterator - regex_replace(OutputIterator out, - BidirectionalIterator first, BidirectionalIterator last, - const basic_regex<charT, traits>& e, - const charT* fmt, - regex_constants::match_flag_type flags = - regex_constants::match_default);</ins> -</pre> -<p>...</p> -<pre> -template <class traits, class charT> - basic_string<charT> - regex_replace(const basic_string<charT>& s, - const basic_regex<charT, traits>& e, - const basic_string<charT>& fmt, - regex_constants::match_flag_type flags = - regex_constants::match_default); - -<ins>template <class traits, class charT> - basic_string<charT> - regex_replace(const basic_string<charT>& s, - const basic_regex<charT, traits>& e, - const charT* fmt, - regex_constants::match_flag_type flags = - regex_constants::match_default);</ins> - -<ins>template <class traits, class charT> - basic_string<charT> - regex_replace(const charT* s, - const basic_regex<charT, traits>& e, - const basic_string<charT>& fmt, - regex_constants::match_flag_type flags = - regex_constants::match_default);</ins> - -<ins>template <class traits, class charT> - basic_string<charT> - regex_replace(const charT* s, - const basic_regex<charT, traits>& e, - const charT* fmt, - regex_constants::match_flag_type flags = - regex_constants::match_default);</ins> -</pre> -</blockquote> - - - - - - -<hr> -<h3><a name="729"></a>729. Problem in [rand.req.eng]/3</h3> -<p><b>Section:</b> 26.5.1.4 [rand.req.eng] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2007-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.req.eng">issues</a> in [rand.req.eng].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The 3rd table row in 26.5.1.4 [rand.req.eng]/3 requires random number engines to accept any -arithmetic type as a seed, which is then casted to the engine's <tt>result_type</tt> and subsequently -used for seeding the state of the engine. The requirement stated as "Creates an engine with -initial state determined by <tt>static_cast<X::result_type>(s)</tt>" forces random number engines -to either use a seeding method that completely depends on the <tt>result_type</tt> (see the discussion -of seeding for the <tt>mersenne_twister_engine</tt> in point T2 above) or at least to throw away "bits -of randomness" in the seed value if the <tt>result_type</tt> is smaller than the seed type. This seems -to be inappropriate for many modern random number generators, in particular F2-linear or -cryptographic ones, which operate on an internal bit array that in principle is independent of the -type of numbers returned. -</p> - -<p> -<b>Possible resolution:</b> I propose to change the wording to a version similar to "Creates an -engine with initial state determined by <tt>static_cast<UintType>(s)</tt>, where <tt>UintType</tt> is an -implementation specific unsigned integer type." -</p> - -<p> -Additionally, the definition of s in 26.5.1.4 [rand.req.eng]/1 c) could be restricted to unsigned integer types. -</p> - -<p> -Similarly, the type of the seed in 26.5.1.5 [rand.req.adapt]/3 e) could be left unspecified. -</p> - -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for further discussion. -</p> - -<p><i>[ -Stephan Tolksdorf adds pre-Bellevue: -]</i></p> - - -<blockquote> -<p> -In reply to the discussion in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -regarding this issue: -</p> -<p> -The descriptions of all engines and engine adaptors given in sections -26.5.3 [rand.eng] and 26.5.4 [rand.adapt] already specify the concrete -types of the integer arguments for seeding. Hence, relaxing the general -requirement in 26.5.1.4 [rand.req.eng] would not affect portability and -reproducibility of the standard library. Furthermore, it is not clear to -me what exactly the guarantee "with initial state determined by -<tt>static_cast<X::result_type>(s)</tt>" is useful for. On the other hand, -relaxing the requirement would allow developers to implement other -random number engines that do not have to cast all arithmetic seed -arguments to their result_types. -</p> -</blockquote> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Propose close NAD for the reasons given in N2424. -</p></blockquote> - - - - -<p><b>Proposed resolution:</b></p> -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for further discussion. -</p> - -<p><i>[ -Stephan Tolksdorf adds pre-Bellevue: -]</i></p> - - -<blockquote> -<p> -Change row 3 of table 105 "Random number engine requirements" in 26.5.1.4 [rand.req.eng]/3 -</p> - -<blockquote><p> -Creates an engine with initial state determined by -<tt><del>static_cast<X::result_type>(</del>s<del>)</del></tt> -</p></blockquote> - -<p> -Similarly, change 26.5.1.5 [rand.req.adapt]/3 e) -</p> - -<blockquote><p> -When <tt>X::X</tt> is invoked with <del>an <tt>X::result_type</tt></del> value <tt>s</tt> -<ins>of arithmetic type (3.9.1)</ins>, ... -</p></blockquote> - -</blockquote> - - - - - - -<hr> -<h3><a name="730"></a>730. Comment on [rand.req.adapt]/3 e)</h3> -<p><b>Section:</b> 26.5.1.5 [rand.req.adapt] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2007-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -If an engine adaptor is invoked with an argument of type <tt>seed_seq</tt>, then all base -engines are specified to be seeded with this <tt>seed_seq</tt>. As <tt>seed_seq</tt>'s randomization method is -qualified as constant, this procedure will ef fectively initialize all base engines with the same seed -(though the resulting state might still dif fer to a certain degree if the engines are of different types). -It is not clear whether this mode of operation is in general appropriate, hence -- as far as the -stated requirements are of general nature and not just specific to the engine adaptors provided by -the library -- it might be better to leave the behaviour unspecified, since the current definition of -<tt>seed_seq</tt> does not allow for a generally satisfying specification. -</p> - -<p> -<b>Posssible resolution:</b> [As above] -</p> - -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for further discussion. -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Close NAD for the reasons given in N2424. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for the proposed resolution. -</p> - - - - - -<hr> -<h3><a name="731"></a>731. proposal for a customizable <tt>seed_seq</tt></h3> -<p><b>Section:</b> 26.5.7.1 [rand.util.seedseq] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2007-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.util.seedseq">issues</a> in [rand.util.seedseq].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The proper way to seed random number engines seems to be the most frequently -discussed issue of the 26.5 [rand] proposal. While the new <tt>seed_seq</tt> approach is already rather -general and probably sufficient for most situations, it is unlikely to be optimal in every case (one -problem was pointed out in point T5 above). In some situations it might, for instance, be better to -seed the state with a cryptographic generator. -</p> -<p> -In my opinion this is a pretty strong argument for extending the standard with a simple facility to -customize the seeding procedure. This could, for example, be done with the following minimal -changes: -</p> - -<p> -<b>Possible resolution:</b> -</p> - -<ol style="list-style-type:lower-alpha"> -<li> -Turn the interface specification of 26.5.7.1 [rand.util.seedseq]/2 into a "SeedSeq" requirement, where the -exact behaviour of the constructors and the randomize method are left unspecified and where the -const qualification for randomize is removed. Classes implementing this interface are additionally -required to specialize the traits class in c). -</li> -<li> -Provide the class <tt>seed_seq</tt> as a default implementation of the SeedSeq interface. -</li> -<li> -<p> -Supplement the <tt>seed_seq</tt> with a traits class -</p> -<blockquote><pre> -template <typename T> -struct is_seed_seq { static const bool value = false; } -</pre></blockquote> -<p>and the specialization</p> -<blockquote><pre> -template <> -struct is_seed_seq<seed_seq> { static const bool value = true; } -</pre></blockquote> -<p>which users can supplement with further specializations.</p> -</li> -<li> -Change 26.5.1.4 [rand.req.eng]/1 d) to "q is an lvalue of a type that fulfils the SeedSeq requirements", and -modify the constructors and seed methods in 26.5.3 [rand.eng] appropriately (the actual implementation -could be done using the SFINAE technique). -</li> -</ol> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -See N2424. Close NAD but note that "conceptizing" the library may cause -this problem to be solved by that route. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for the proposed resolution. -</p> - - - - - -<hr> -<h3><a name="733"></a>733. Comment on [rand.req.dist]/9</h3> -<p><b>Section:</b> 26.5.1.6 [rand.req.dist] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2007-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The requirement "P shall have a declaration of the form <tt>typedef X distribution_- -type</tt>" effectively makes the use of inheritance for implementing distributions very inconvenient, -because the child of a distribution class in general will not satisfy this requirement. In my opinion -the benefits of having a typedef in the parameter class pointing back to the distribution class are -not worth the hassle this requirement causes. [In my code base I never made use of the nested -typedef but on several occasions could have profited from being able to use simple inheritance for -the implementation of a distribution class.] -</p> - -<p> -<b>Proposed resolution:</b> I propose to drop this requirement. -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Close NAD for the reasons given in N2424. In practice it is not inconvenient to meet these requirements. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for the proposed resolution. -</p> - - - - - -<hr> -<h3><a name="735"></a>735. Unfortunate naming</h3> -<p><b>Section:</b> 26.5.8.3.2 [rand.dist.bern.bin], 26.5.8.3.4 [rand.dist.bern.negbin] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2007-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In my opinion the choice of name for the <tt>t</tt> parameter of the <tt>binomial_distribution</tt> -is very unfortunate. In virtually every internet reference, book and software implementation -this parameter is called <tt>n</tt> instead, see for example Wikipedia, Mathworld, Evans et al. (1993) -Statistical Distributions, 2nd E., Wiley, p. 38, the R statistical computing language, p. 926, -Mathematica and Matlab. -</p> - -<p> -Similarly, the choice of <tt>k</tt> for the parameter of the negative binomial distributions is rather unusual. -The most common choice for the negative binomial distribution seems to be <tt>r</tt> instead. -</p> - -<p> -Choosing unusual names for the parameters causes confusion among users and makes the -interface unnecessarily inconvenient to use. -</p> - -<p> -<b>Possible resolution:</b> For these reasons, I propose to change the name of the respective parameters -to <tt>n</tt> and <tt>r</tt>. -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -In N2424. NAD It has been around for a while. It is hardly universal, -there is prior art, and this would confuse people. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for the proposed resolution. -</p> - - - - - -<hr> -<h3><a name="736"></a>736. Comment on [rand.dist.samp.discrete]</h3> -<p><b>Section:</b> 26.5.8.6.1 [rand.dist.samp.discrete] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2007-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.dist.samp.discrete">issues</a> in [rand.dist.samp.discrete].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<ol style="list-style-type:lower-alpha"> -<li> -The specification for <tt>discrete_distribution</tt> requires the member <tt>probabilities()</tt> -to return a vector of <i>standardized</i> probabilities, which forces the implementation every time to -divide each probability by the sum of all probabilities, as the sum will in practice almost never be -exactly 1.0. This is unnecessarily inef ficient as the implementation would otherwise not need to -compute the standardized probabilities at all and could instead work with the non-standardized -probabilities and the sum. If there was no standardization the user would just get back the -probabilities that were previously supplied to the distribution object, which to me seems to be the -more obvious solution. -</li> -<li> -The behaviour of <tt>discrete_distribution</tt> is not specified in case the number of given -probabilities is larger than the maximum number representable by the IntType. -</li> -</ol> - -<p> -<b>Possible resolution:</b> I propose to change the specification such that the non-standardized -probabilities need to be returned and that an additional requirement is included for the number -of probabilities to be smaller than the maximum of IntType. -</p> - -<p><i>[ -Stephan Tolksdorf adds pre-Bellevue: -]</i></p> - - -<blockquote> -<p> -In reply to the discussion in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -of this issue: -</p> -<p> -Rescaled floating-point parameter vectors can not be expected to compare -equal because of the limited precision of floating-point numbers. -My proposal would at least guarantee that a parameter -vector (of type double) passed into the distribution would compare equal -with the one returned by the <tt>probabilities()</tt> method. Furthermore, I do -not understand why "the changed requirement would lead to a significant -increase in the amount of state in the distribution object". A typical -implementation's state would increase by exactly one number: the sum of -all probabilities. The textual representation for serialization would -not need to grow at all. Finally, the proposed replacement "<tt>0 < n <= -numeric_limits<IntType>::max() + 1</tt>" makes the implementation -unnecessarily complicated, "<tt>0 < n <= numeric_limits<IntType>::max()</tt>" -would be better. -</p> -</blockquote> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote> -<p> -In N2424. We agree with the observation and the proposed resolution to -part b). We recommend the wording n > 0 be replaced with 0 < n -numeric_limits::max() + 1. However, we disagree with part a), as it -would interfere with the definition of parameters' equality. Further, -the changed requirement would lead to a significant increase in the -amount of state of the distribution object. -</p> - -<p> -As it stands now, it is convenient, and the changes proposed make it -much less so. -</p> - -<p> -NAD. Part a the current behavior is desirable. Part b, any constructor -can fail, but the rules under which it can fail do not need to be listed -here. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for the proposed resolution. -</p> - -<p><i>[ -Stephan Tolksdorf adds pre-Bellevue: -]</i></p> - - -<blockquote> -<p> -In 26.5.8.6.1 [rand.dist.samp.discrete]: -</p> - -<p> -Proposed wording a): -</p> - -<blockquote> -<p> -Change in para. 2 -</p> - -<blockquote><p> -Constructs a <tt>discrete_distribution</tt> object with <tt>n=1</tt> and <tt>p<sub>0</sub> <ins>= w<sub>0</sub></ins> = 1</tt> -</p></blockquote> - -<p> -and change in para. 5 -</p> - -<blockquote><p> -<i>Returns:</i> A <tt>vector<double></tt> whose <tt>size</tt> member returns <tt>n</tt> and whose -<tt>operator[]</tt> member returns <del><tt>p<sub>k</sub></tt></del> -<ins>the weight <tt>w<sub>k</sub></tt> as a double value</ins> -when invoked with argument <tt>k</tt> for <tt>k = 0, -..., n-1</tt> -</p></blockquote> - -</blockquote> - -<p> -Proposed wording b): -</p> - -<blockquote> -<p> -Change in para. 3: -</p> - -<blockquote><p> -If <tt>firstW == lastW</tt>, let the sequence <tt>w</tt> have length <tt>n = 1</tt> and consist -of the single value <tt>w<sub>0</sub> = 1</tt>. Otherwise, <tt>[firstW,lastW)</tt> shall form a -sequence <tt>w</tt> of length <tt>n <del>> 0</del></tt> -<ins>such that <tt>0 < n <= numeric_limits<IntType>::max()</tt>,</ins> -and <tt>*firstW</tt> shall yield a value <tt>w<sub>0</sub></tt> -convertible to <tt>double</tt>. [<i>Note:</i> The values <tt>w<sub>k</sub></tt> are commonly known -as the weights . <i>-- end note</i>] -</p></blockquote> - -</blockquote> - -</blockquote> - - - - - -<hr> -<h3><a name="737"></a>737. Comment on [rand.dist.samp.pconst]</h3> -<p><b>Section:</b> 26.5.8.6.2 [rand.dist.samp.pconst] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2007-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.dist.samp.pconst">issues</a> in [rand.dist.samp.pconst].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<ol style="list-style-type:lower-alpha"> -<li> -The discussion in point T11 above regarding <tt>probabilities()</tt> similarly applies -to the method <tt>densities()</tt> of <tt>piecewise_constant_distribution</tt>. -</li> -<li> -<p> -The design of the constructor -</p> -<blockquote><pre> -template <class InputIteratorB, class InputIteratorW> -piecewise_constant_distribution( InputIteratorB firstB, InputIteratorB lastB, - InputIteratorW firstW); -</pre></blockquote> -<p> -is unnecessarily unsafe, as there is no separate end-iterator given for the weights. I can't see -any performance or convenience reasons that would justify the risks inherent in such a function -interface, in particular the risk that input error might go unnoticed. -</p> -</li> -</ol> - -<p> -<b>Possible resolution:</b> I propose to add an <tt>InputIteratorW lastW</tt> argument to the interface. -</p> - -<p><i>[ -Stephan Tolksdorf adds pre-Bellevue: -]</i></p> - -<blockquote><p> -In reply to the discussion in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -I'd like to make the same comments as for <a href="lwg-closed.html#736">736</a>. -</p></blockquote> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -In N2424. There is already precedent elsewhere in the library. Follows existing convention. NAD. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for the proposed resolution. -</p> - -<p><i>[ -Stephan Tolksdorf adds pre-Bellevue: -]</i></p> - - -<blockquote> -<p> -In 26.5.8.6.2 [rand.dist.samp.pconst]: -</p> - -<p> -Proposed wording a) -</p> - -<blockquote> -<p> -Change in para. 2 -</p> -<blockquote><p> -Constructs a <tt>piecewise_constant_distribution</tt> object with <tt>n = 1</tt>, <tt>p<sub>0</sub> <ins>= w<sub>0</sub></ins> = 1</tt>, -<tt>b<sub>0</sub> = 0</tt>, and <tt>b<sub>1</sub> = 1</tt> -</p></blockquote> - -<p> -and change in para. 5 -</p> - -<blockquote><p> -A <tt>vector<result_type></tt> whose <tt>size</tt> member returns <tt>n</tt> and whose <tt>operator[]</tt> -member returns <del><tt>p<sub>k</sub></tt></del> -<ins>the weight <tt>w<sub>k</sub></tt> as a double value</ins> -when invoked with argument <tt>k</tt> for <tt>k = 0, ..., n-1</tt> -</p></blockquote> - -</blockquote> - -<p> -Proposed wording b) -</p> - -<blockquote> -<p> -Change both occurrences of -</p> - -<blockquote><pre> -"piecewise_constant_distribution(InputIteratorB firstB, InputIteratorB lastB, - InputIteratorW firstW<ins>, InputIteratorW lastW</ins>) -</pre></blockquote> - -<p> -and change in para. 3 -</p> - -<blockquote><p> -<del>the length of the sequence <tt>w</tt> starting from <tt>firstW</tt> shall be at least <tt>n</tt>, -<tt>*firstW</tt> shall return a value <tt>w<sub>0</sub></tt> that is convertible to <tt>double</tt>, and any -<tt>w<sub>k</sub></tt> for <tt>k >= n</tt> shall be ignored by the distribution</del> -<ins><tt>[firstW, lastW)</tt> shall form a sequence <tt>w</tt> of length <tt>n</tt> whose leading element -<tt>w<sub>0</sub></tt> shall be convertible to <tt>double</tt></ins> -</p></blockquote> - -</blockquote> - - -</blockquote> - - - - - - -<hr> -<h3><a name="738"></a>738. Editorial issue in [rand.adapt.disc]/3</h3> -<p><b>Section:</b> 26.5.4.2 [rand.adapt.disc] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2007-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.adapt.disc">issues</a> in [rand.adapt.disc].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Since the template parameter <tt>p</tt> and <tt>r</tt> are of type <tt>size_t</tt>, the member <tt>n</tt> in the class -exposition should have type <tt>size_t</tt>, too. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for the proposed resolution. -</p> - - - - - -<hr> -<h3><a name="739"></a>739. Defect in [rand.util.canonical]/3</h3> -<p><b>Section:</b> 26.5.7.2 [rand.util.canonical] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2007-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.util.canonical">issues</a> in [rand.util.canonical].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The complexity of <tt>generate_canonical</tt> is specified to be "exactly k=max(1, ceil(b/log2 -R)) invocations of g". This terms involves a logarithm that is not rounded and hence can not (in -general) be computed at compile time. As this function template is performance critical, I propose -to replace ceil(b/log2 R) with ceil(b/floor(log2 R)). -</p> - -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for further discussion. -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -In N2424. Close NAD as described there. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2424.pdf">N2424</a> -for the proposed resolution. -</p> - - - - - -<hr> -<h3><a name="741"></a>741. Const-incorrect <tt>get_deleter</tt> function for <tt>shared_ptr</tt></h3> -<p><b>Section:</b> 20.8.2.2.10 [util.smartptr.getdeleter] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-09-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#util.smartptr.getdeleter">issues</a> in [util.smartptr.getdeleter].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The following issue was raised by Alf P. Steinbach in c.l.c++.mod: -</p> - -<p> -According to the recent draft N2369, both the header memory synopsis -of 20.7 [memory] and 20.8.2.2.10 [util.smartptr.getdeleter] declare: -</p> - -<blockquote><pre> -template<class D, class T> D* get_deleter(shared_ptr<T> const& p); -</pre></blockquote> - -<p> -This allows to retrieve the pointer to a mutable deleter of a <tt>const -shared_ptr</tt> (if that owns one) and therefore contradicts the usual -philosophy that associated functors are either read-only (e.g. -<tt>key_comp</tt> or <tt>value_comp</tt> of <tt>std::map</tt>) or do at least reflect -the mutability of the owner (as seen for the both overloads of -<tt>unique_ptr::get_deleter</tt>). -Even the next similar counter-part of <tt>get_deleter</tt> - the two -overloads of <tt>function::target</tt> in the class template function -synopsis 20.9.12.2 [func.wrap.func] or in 20.9.12.2.5 [func.wrap.func.targ] - do -properly mirror the const-state of the owner. -</p> - -<p><b>Possible proposed resolutions:</b></p> - -<p> -Replace the declarations of <tt>get_deleter</tt> in the header <tt><memory></tt> -synopsis of 20.7 [memory] and in 20.8.2.2.10 [util.smartptr.getdeleter] by one of the -following alternatives (A) or (B): -</p> - -<ol style="list-style-type:upper-alpha"> -<li> -Provide <b>only</b> the immutable variant. This would reflect the -current praxis of <tt>container::get_allocator()</tt>, <tt>map::key_comp()</tt>, or -<tt>map::value_comp</tt>. - -<blockquote><pre> -template<class D, class T> const D* get_deleter(shared_ptr<T> const& p); -</pre></blockquote> -</li> -<li> -Just remove the function. -</li> -</ol> - -<p> -Alberto Ganesh Barbati adds: -</p> - -<ol style="list-style-type:upper-alpha" start="3"> -<li> -<p> -Replace it with two functions: -</p> -<blockquote><pre> -template <class D, class T> D get_deleter(shared_ptr<T> const&); -template <class D, class T> bool has_deleter(shared_ptr<T> const&); -</pre></blockquote> - -<p> -The first one would throw if <tt>D</tt> is the wrong type, while the latter would -never throw. This approach would reflect the current praxis of -<tt>use_facet/has_facet</tt>, with the twist of returning the deleter by value as -<tt>container::get_allocator()</tt> do. -</p> -</li> -</ol> - -<p> -Peter Dimov adds: -</p> - -<blockquote> -<p> -My favorite option is "not a defect". A, B and C break useful code. -</p> -</blockquote> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Concern this is similar to confusing "pointer to const" with "a constant pointer". -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="745"></a>745. copy_exception API slices.</h3> -<p><b>Section:</b> 18.8.5 [propagation] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2007-10-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#propagation">issues</a> in [propagation].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -It could be I did not understand the design rationale, but I thought -copy_exception would produce an exception_ptr to the most-derived (dynamic) -type of the passed exception. Instead it slices, which appears to be less -useful, and a likely source of FAQ questions in the future. -</p> -<p> -(Peter Dimov suggests NAD) -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote> -<p> -How could this be implemented in a way that the dynamic type is cloned? -</p> -<p> -The feature is designed to create an exception_ptr from an object whose -static type is identical to the dynamic type and thus there is no -slicing involved. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="747"></a>747. We have 3 separate type traits to identify classes supporting no-throw operations</h3> -<p><b>Section:</b> 20.10.4.3 [meta.unary.prop] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2007-10-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#meta.unary.prop">active issues</a> in [meta.unary.prop].</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.unary.prop">issues</a> in [meta.unary.prop].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -We have 3 separate type traits to identify classes supporting no-throw -operations, which are very useful when trying to provide exception safety -guarantees. However, I'm not entirely clear on what the current wording -requires of a conforming implementation. To quote from -<tt>has_nothrow_default_constructor</tt>: -</p> -<blockquote><p> -or <tt>T</tt> is a class type with a default constructor that is known not to throw -any exceptions -</p></blockquote> -<p> -What level of magic do we expect to deduce if this is known? -</p> -<p> -E.g. -</p> - -<blockquote><pre> -struct test{ - int x; - test() : x() {} -}; -</pre></blockquote> -<p> -Should I expect a conforming compiler to - <tt>assert( has_nothrow_constructor<test>::value )</tt> -</p> -<p> -Is this a QoI issue? -</p> -<p> -Should I expect to 'know' only if-and-only-if there is an inline definition -available? -</p> -<p> -Should I never expect that to be true, and insist that the user supplies an -empty throw spec if they want to assert the no-throw guarantee? -</p> -<p> -It would be helpful to maybe have a footnote explaining what is required, -but right now I don't know what to suggest putting in the footnote. -</p> -<p> -(agreement since is that trivial ops and explicit no-throws are required. -Open if QoI should be allowed to detect further) -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -This looks like a QoI issue. -In the case of trivial and nothrow it is known. Static analysis of the program is definitely into QoI. -Move to OPEN. Need to talk to Core about this. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote> -<p> -This is QoI. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="748"></a>748. The is_abstract type trait is defined by reference to 10.4.</h3> -<p><b>Section:</b> 20.10.4.3 [meta.unary.prop] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2007-10-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#meta.unary.prop">active issues</a> in [meta.unary.prop].</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.unary.prop">issues</a> in [meta.unary.prop].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I am trying to decide is a pure virtual function is a <i>necessary</i> as well as -sufficient requirement to be classified as abstract? -</p> -<p> -For instance, is the following (non-polymorphic) type considered abstract? -</p> -<blockquote><pre> -struct abstract { -protected: - abstract(){} - abstract( abstract const & ) {} - ~abstract() {} -}; -</pre></blockquote> -<p> -(Suggested that this may be NAD, with an editorial fix-up from Pete on the -core wording to make clear that abstract requires a pure virtual function) -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Core has clarified that the definition abstract is adequate. Issue withdrawn by submitter. NAD. -</p> - - - - - -<hr> -<h3><a name="750"></a>750. The current definition for <tt>is_convertible</tt> requires that the type be -implicitly convertible, so explicit constructors are ignored.</h3> -<p><b>Section:</b> 20.10.6 [meta.rel] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2007-10-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.rel">issues</a> in [meta.rel].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#719">719</a></p> -<p><b>Discussion:</b></p> -<p> -With the pending arrival of explicit conversion functions though, I'm -wondering if we want an additional trait, <tt>is_explictly_convertible</tt>? -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Alisdair is considering preparing a paper listing a number of missing -type traits, and feels that it might be useful to handle them all -together rather than piecemeal. This would affect issue 719 and 750. -These two issues should move to OPEN pending AM paper on type traits. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Duplicate of <a href="lwg-defects.html#719">719</a> (for our purposes). -</p></blockquote> - -<p><i>[ -Addressed in <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2947.html">N2947</a>. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> - - - - - - -<hr> -<h3><a name="751"></a>751. change pass-by-reference members of <tt>vector<bool></tt> to pass-by-value?</h3> -<p><b>Section:</b> 23.3.7 [vector.bool] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2007-10-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#vector.bool">issues</a> in [vector.bool].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -A number of <tt>vector<bool></tt> members take const bool& as arguments. -Is there any chance we could change them to pass-by-value or would I -be wasting everyone's time if wrote up an issue? -</p> - -<p><i>[ -post Bellevue: -]</i></p> - - -<blockquote> -<p> -As we understand it, the original requester (Martin Sebor) would like -for implementations to be permitted to pass-by-value. Alisdair suggests -that if this is to be resolved, it should be resolved more generally, -e.g. in other containers as well. -</p> -<p> -We note that this would break ABI. However, we also suspect that this -might be covered under the "as-if" rule in section 1.9. -</p> -<p> -Many in the group feel that for vector<bool>, this is a "don't care", -and that at this point in the process it's not worth the bandwidth. -</p> -<p> -Issue <a href="lwg-defects.html#679">679</a> -- which was in ready status pre-Bellevue and is -now in the working paper -- is related to this, though not a duplicate. -</p> -<p> -Moving to Open with a task for Alisdair to craft a informative note to -be put whereever appropriate in the WP. This note would clarify places -where pass-by-const-ref can be transformed to pass-by-value under the -as-if rule. -</p> -</blockquote> - -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote> -<p> -This is really a clause 17 issue, rather than something specific to vector<bool>. -</p> -<p> -Move to Open. Alisdair to provide a resolution. Alternately, Howard can -close this as NAD and then open a new issue to handle the general issue -(rather than the vector<bool> one). -</p> -<p> -Howard: Haven't yet opened new issue. Lacking wording for it. -</p> -</blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -NAD. Insufficient motivation to make any changes. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="754"></a>754. Ambiguous return clause for <tt>std::uninitialized_copy</tt></h3> -<p><b>Section:</b> 20.7.12.2 [uninitialized.copy] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2007-10-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#uninitialized.copy">issues</a> in [uninitialized.copy].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -14882-2003, [lib.uninitialized.copy] is currently written as follows: -</p> - -<blockquote> -<pre> -template <class InputIterator, class ForwardIterator> - ForwardIterator uninitialized_copy(InputIterator <i>first</i>, InputIterator <i>last</i>, - ForwardIterator <i>result</i>); -</pre> -<blockquote> -<p> --1- <i>Effects:</i> -</p> -<blockquote><pre> -for (; first != last; ++result, ++first) - new (static_cast<void*>(&*result)) - typename iterator_traits<ForwardIterator>::value_type(*first); -</pre></blockquote> -<p> --2- <i>Returns:</i> <tt><i>result</i></tt> -</p> -</blockquote> -</blockquote> - -<p> -similarily for N2369, and its corresponding section -20.7.12.2 [uninitialized.copy]. -</p> - -<p> -It's not clear to me what the return clause is supposed to mean, I see -two -possible interpretations: -</p> - -<ol style="list-style-type:lower-alpha"> -<li> -The notion of <tt><i>result</i></tt> is supposed to mean the value given by the -function parameter <tt><i>result</i></tt> [Note to the issue editor: Please use italics for -<tt><i>result</i></tt>]. -This seems somewhat implied by recognizing that both the function -parameter -and the name used in the clause do have the same italic font. -</li> -<li> -The notion of "result" is supposed to mean the value of <tt><i>result</i></tt> -after the -preceding effects clause. This is in fact what all implementations I -checked -do (and which is probably it's intend, because it matches the -specification of <tt>std::copy</tt>). -</li> -</ol> - -<p> -The problem is: I see nothing in the standard which grants that this -interpretation -is correct, specifically [lib.structure.specifications] or -17.5.1.4 [structure.specifications] -resp. do not clarify which "look-up" rules apply for names found in -the elements -of the detailed specifications - Do they relate to the corresponding -synopsis or -to the effects clause (or possibly other elements)? Fortunately most -detailed -descriptions are unambigious in this regard, e.g. this problem does -not apply -for <tt>std::copy</tt>. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change the wording of the return clause to say (20.7.12.2 [uninitialized.copy]): -</p> - -<blockquote> -<p> --2- <i>Returns:</i> <ins>The value of</ins> <tt><i>result</i></tt> <ins>after effects have taken place.</ins> -</p> -</blockquote> - - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Resolution: NAD editorial -- project editor to decide if change is -worthwhile. Concern is that there are many other places this might -occur. -</p></blockquote> - - - - -<hr> -<h3><a name="757"></a>757. Typo in the synopsis of vector</h3> -<p><b>Section:</b> 23.3.6 [vector] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Paolo Carlini <b>Opened:</b> 2007-11-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#vector">issues</a> in [vector].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In the synopsis 23.3.6 [vector], there is the signature: -</p> - -<blockquote><pre> -void insert(const_iterator position, size_type n, T&& x); -</pre></blockquote> - -<p> -instead of: -</p> - -<blockquote><pre> -iterator insert(const_iterator position, T&& x); -</pre></blockquote> - -<p> -23.3.6.5 [vector.modifiers] is fine. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change the synopsis in 23.3.6 [vector]: -</p> - -<blockquote><pre> -iterator insert(const_iterator position, const T& x); -<ins>iterator insert(const_iterator position, T&& x);</ins> -void insert(const_iterator position, size_type n, const T& x); -<del>void insert(const_iterator position, size_type n, T&& x);</del> -</pre></blockquote> - - - - - -<hr> -<h3><a name="763"></a>763. Renaming <tt>emplace()</tt> overloads</h3> -<p><b>Section:</b> 23.2.4 [associative.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Sylvain Pion <b>Opened:</b> 2007-12-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The associative containers provide 2 overloads of <tt>emplace()</tt>: -</p> - -<blockquote><pre> -template <class... Args> pair<iterator, bool> emplace(Args&&... args); -template <class... Args> iterator emplace(const_iterator position, Args&&... args); -</pre></blockquote> - -<p> -This is a problem if you mean the first overload while passing -a <tt>const_iterator</tt> as first argument. -</p> - -<p><i>[ -Related to <a href="lwg-defects.html#767">767</a> -]</i></p> - - -<p><i>[ -Bellevue: -]</i></p> - - -<p> -This can be disambiguated by passing "begin" as the first argument in -the case when the non-default choice is desired. We believe that desire -will be rare. -</p> - -<p><i>[For related discussion see <a href="lwg-closed.html#1302">1302</a>]</i></p> - - -<p> -LWG <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2680.pdf">N2680</a> -renamed one of the overloads to <tt>emplace_hint</tt>. -</p> - -<p> -Resolution: Change state to NAD. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Rename one of the two overloads. -For example to <tt>emplace_here</tt>, <tt>hint_emplace</tt>... -</p> - - - - - -<hr> -<h3><a name="764"></a>764. <tt>equal_range</tt> on unordered containers should return a <tt>pair</tt> of <tt>local_iterators</tt></h3> -<p><b>Section:</b> 23.2.5 [unord.req] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Joe Gottman <b>Opened:</b> 2007-11-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#unord.req">active issues</a> in [unord.req].</p> -<p><b>View all other</b> <a href="lwg-index.html#unord.req">issues</a> in [unord.req].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> - A major attribute of the unordered containers is that iterating -though them inside a bucket is very fast while iterating between buckets -can be much slower. If an unordered container has a low load factor, -iterating between the last iterator in one bucket and the next iterator, -which is in another bucket, is <tt>O(bucket_count())</tt> which may be much -larger than <tt>O(size())</tt>. -</p> -<p> - If <tt>b</tt> is an non-const unordered container of type <tt>B</tt> and <tt>k</tt> is an -object of it's <tt>key_type</tt>, then <tt>b.equal_range(k)</tt> currently returns -<tt>pair<B::iterator, B::iterator></tt>. Consider the following code: -</p> - -<blockquote><pre> -B::iterator lb, ub; -tie(lb, ub) = b.equal_range(k); -for (B::iterator it = lb; it != ub; ++it) { - // Do something with *it -} -</pre></blockquote> - -<p> -If <tt>b.equal_range(k)</tt> returns a non-empty range (i.e. <tt>b</tt> contains at least -on element whose key is equivalent to <tt>k</tt>), then every iterator in the -half-open range <tt>[lb, ub)</tt> will be in the same bucket, but <tt>ub</tt> will likely -either be in a different bucket or be equal to <tt>b.end()</tt>. In either case, -iterating between <tt>ub - 1</tt> and <tt>ub</tt> could take a much longer time than -iterating through the rest of the range. -</p> -<p> -If instead of returning <tt>pair<iterator, iterator></tt>, <tt>equal_range</tt> were to -return <tt>pair<local_iterator, local_iterator></tt>, then <tt>ub</tt> (which, like <tt>lb</tt>, -would now be a <tt>local_iterator</tt>) could be guaranteed to always be in the -same bucket as <tt>lb</tt>. In the cases where currently <tt>ub</tt> is equal to <tt>b.end()</tt> -or is in a different bucket, <tt>ub</tt> would be equal to <tt>b.end(b.bucket(key))</tt>. - This would make iterating between <tt>lb</tt> and <tt>ub</tt> much faster, as every -iteration would be constant time. -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -The proposed resolution breaks consistency with other container types -for dubious benefit, and iterators are already constant time. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change the entry for <tt>equal_range</tt> in Table 93 (23.2.5 [unord.req]) as follows: -</p> -<table border="1"> -<tr> -<th>expression</th> <th>return type</th> <th>assertion/note pre/post-condition</th> <th>complexity</th> -</tr> - -<tr> -<td><tt>b.equal_range(k)</tt></td> -<td><tt>pair<<ins>local_</ins>iterator,<ins>local_</ins>iterator>; pair<const_<ins>local_</ins>iterator,const_<ins>local_</ins>iterator></tt> for <tt>const b</tt>.</td> -<td>Returns a range containing all elements with keys equivalent to <tt>k</tt>. Returns <tt>make_pair(b.end(<ins>b.bucket(key)</ins>),b.end(<ins>b.bucket(key)</ins>))</tt> if no such elements exist.</td> -<td>Average case Θ<tt>(b.count(k))</tt>. Worst case Θ<tt>(b.size())</tt>. </td> -</tr> -</table> - - - - - -<hr> -<h3><a name="773"></a>773. issues with random</h3> -<p><b>Section:</b> 26.5.8.2 [rand.dist.uni] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2008-01-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.dist.uni">issues</a> in [rand.dist.uni].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<ol> -<li> -26.5.8.2.1 [rand.dist.uni.int] <tt>uniform_int</tt> constructor has changed the default -max constructor parameter from 9 (in TR1) to <tt>max()</tt>. The value -is arbitrary at best and shouldn't be lightly changed because -it breaks backward compatibility. -</li> - -<li> -26.5.8.2.1 [rand.dist.uni.int] <tt>uniform_int</tt> has a parameter <tt>param</tt> that you can -provide on construction or <tt>operator()</tt>, set, and get. But there -is not even a hint of what this might be for. -</li> - -<li> -26.5.8.2.2 [rand.dist.uni.real] <tt>uniform_real</tt>. Same issue as #2. -</li> -</ol> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -NAD. Withdrawn. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="784"></a>784. unique_lock::release</h3> -<p><b>Section:</b> 30.4.2.2.3 [thread.lock.unique.mod] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Constantine Sapuntzakis <b>Opened:</b> 2008-02-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -<tt>unique_lock::release</tt> will probably lead to many mistakes where people -call <tt>release</tt> instead of <tt>unlock</tt>. I just coded such a mistake using the -boost pre-1.35 threads library last week. -</p> - -<p> -In many threading libraries, a call with <tt>release</tt> in it unlocks the -lock (e.g. ReleaseMutex in Win32, java.util.concurrent.Semaphore). -</p> - -<p> -I don't call <tt>unique_lock::lock</tt> much at all, so I don't get to see the -symmetry between <tt>::lock</tt> and <tt>::unlock</tt>. I usually use the constructor to -lock the mutex. So I'm left to remember whether to call <tt>release</tt> or -<tt>unlock</tt> during the few times I need to release the mutex before the scope -ends. If I get it wrong, the compiler doesn't warn me. -</p> - -<p> -An alternative name for release may be <tt>disown</tt>. -</p> - -<p> -This might be a rare case where usability is hurt by consistency with -the rest of the C++ standard (e.g. <tt>std::auto_ptr::release</tt>). -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Change a name from release to disown. However prior art uses the release -name. Compatibility with prior art is more important that any possible -benefit such a change might make. We do not see the benefit for -changing. NAD -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change the synopsis in 30.4.2.2 [thread.lock.unique]: -</p> - -<blockquote><pre> -template <class Mutex> -class unique_lock -{ -public: - ... - mutex_type* <del>release</del> <ins>disown</ins>(); - ... -}; -</pre></blockquote> - -<p> -Change 30.4.2.2.3 [thread.lock.unique.mod]: -</p> - -<blockquote><pre> -mutex_type *<del>release</del> <ins>disown</ins>(); -</pre></blockquote> - - - - - -<hr> -<h3><a name="785"></a>785. Random Number Requirements in TR1</h3> -<p><b>Section:</b> TR1 5.1.4.5 [tr.rand.eng.disc], TR1 5.1.4.6 [tr.rand.eng.xor] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> John Maddock <b>Opened:</b> 2008-01-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Table 16 of TR1 requires that all Pseudo Random Number generators have a -</p> - -<blockquote><pre> -seed(integer-type s) -</pre></blockquote> - -<p> -member function that is equivalent to: -</p> - -<blockquote><pre> -mygen = Generator(s) -</pre></blockquote> - -<p> -But the generators <tt>xor_combine</tt> and <tt>discard_block</tt> have no such seed member, only the -</p> - -<blockquote><pre> -template <class Gen> -seed(Gen&); -</pre></blockquote> - -<p> -member, which will not accept an integer literal as an argument: something that appears to violate the intent of Table 16. -</p> - -<p> -So... is this a bug in TR1? -</p> - -<p> -This is a real issue BTW, since the Boost implementation does adhere to the requirements of Table 16, while at least one commercial implementation does not and follows a strict adherence to sections 5.1.4.5 and 5.1.4.6 instead. -</p> - -<p><i>[ -Jens adds: -]</i></p> - - -<blockquote><p> -Both engines do have the necessary -constructor, therefore the omission of the <tt>seed()</tt> member -functions appears to be an oversight. -</p></blockquote> - -<p><i>[ -Post Summit Daniel adds: -]</i></p> - - -<blockquote><p> -Recommend NAD: <tt>xor_combine</tt> does no longer exist and <tt>discard_block[_engine]</tt> -has now the required seed overload accepting a <tt>result_type</tt>, which shall be an -unsigned integral type. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to NAD as recommended. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -NAD Recommended. -</p> - - - - - -<hr> -<h3><a name="790"></a>790. <tt>xor_combine::seed</tt> not specified</h3> -<p><b>Section:</b> X [rand.adapt.xor] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2008-02-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.adapt.xor">issues</a> in [rand.adapt.xor].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -<tt>xor_combine::seed(result_type)</tt> and <tt>seed(seed_seq&)</tt> don't say what -happens to each of the sub-engine seeds. (Should probably do the same -to both, unlike TR1.) -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Overcome by the previous proposal. NAD mooted by resolution of <a href="lwg-defects.html#789">789</a>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="791"></a>791. <tt>piecewise_constant_distribution::densities</tt> has wrong name</h3> -<p><b>Section:</b> 26.5.8.6.2 [rand.dist.samp.pconst] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2008-02-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.dist.samp.pconst">issues</a> in [rand.dist.samp.pconst].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -<tt>piecewise_constant_distribution::densities()</tt> should be <tt>probabilities()</tt>, -just like <tt>discrete_distribution</tt>. (There's no real use for weights divided -by areas.) -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote> -<p> -Fermilab does not agree with this summary. As defined in the equation in -26.4.8.5.2/4, the quantities are indeed probability densities not -probabilities. Because we view this distribution as a parameterization -of a *probability density function*, we prefer to work in terms of -probability densities. -</p> - -<p> -We don't think this should be changed. -</p> - -<p> -If there is a technical argument about why the implementation dealing -with these values can't be as efficient as one dealing with -probabilities, we might reconsider. We don't care about this one member -function being somewhat more or less efficient; we care about the size -of the distribution object and the speed of the calls to generate -variates. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - -<p> -Change synopsis in 26.5.8.6.2 [rand.dist.samp.pconst]: -</p> - -<blockquote><pre> -template <class RealType = double> -class piecewise_constant_distribution -{ -public: - ... - vector<double> <del>densities</del> <ins>probabilities</ins>() const; - ... -}; -</pre></blockquote> - -<p> -Change 26.5.8.6.2 [rand.dist.samp.pconst]/6: -</p> - -<blockquote><pre> -vector<double> <del>densities</del> <ins>probabilities</ins>() const; -</pre></blockquote> - - - - - - -<hr> -<h3><a name="795"></a>795. <tt>general_pdf_distribution</tt> should be dropped</h3> -<p><b>Section:</b> X [rand.dist.samp.genpdf] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2008-02-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.dist.samp.genpdf">issues</a> in [rand.dist.samp.genpdf].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#732">732</a></p> -<p><b>Discussion:</b></p> -<p> -<tt>general_pdf_distribution</tt> should be dropped. (It's a research topic in -adaptive numerical integration.) -</p> - -<p><i>[ -Stephan Tolksdorf notes: -]</i></p> - - -<blockquote><p> -This appears to be a duplicate of <a href="lwg-defects.html#732">732</a>. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - - -<hr> -<h3><a name="796"></a>796. <tt>ranlux48_base</tt> returns wrong value</h3> -<p><b>Section:</b> 26.5.5 [rand.predef] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2008-02-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.predef">issues</a> in [rand.predef].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The 10,000<sup>th</sup> value returned by <tt>ranlux48_base</tt> is supposed to be -61839128582725. We get 192113843633948. (Note that the underlying -generator was changed in Kona.) -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Submitter withdraws defect. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 26.5.5 [rand.predef]/p5: -</p> - -<blockquote> -<pre> -typedef subtract_with_carry_engine<uint_fast64_t, 48, 5, 12> - ranlux48_base; -</pre> -<blockquote><p> -<i>Required behavior:</i> The 10000<sup>th</sup> consecutive invocation of a default-constructed -object of type <tt>ranlux48_base</tt> shall produce the value -<del>61839128582725</del> <ins>192113843633948</ins>. -</p></blockquote> -</blockquote> - - - - - -<hr> -<h3><a name="797"></a>797. <tt>ranlux48</tt> returns wrong value</h3> -<p><b>Section:</b> 26.5.5 [rand.predef] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2008-02-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.predef">issues</a> in [rand.predef].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The 10,000<sup>th</sup> value returned by <tt>ranlux48</tt> is supposed to be -249142670248501. We get 88229545517833. (Note that this depends -on <tt>ranlux48_base</tt>.) -</p> -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote><p> -Submitter withdraws defect. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 26.5.5 [rand.predef]/p6: -</p> - -<blockquote> -<pre> -typedef discard_block_engine<ranlux48_base, 389, 11> - ranlux48 -</pre> -<blockquote><p> -<i>Required behavior:</i> The 10000<sup>th</sup> consecutive invocation of a default-constructed -object of type <tt>ranlux48</tt> shall produce the value -<del>249142670248501</del> <ins>88229545517833</ins>. -</p></blockquote> -</blockquote> - - - - - -<hr> -<h3><a name="799"></a>799. [tr.rand.eng.mers] and [rand.eng.mers]</h3> -<p><b>Section:</b> 26.5.3.2 [rand.eng.mers], TR1 5.1.4.2 [tr.rand.eng.mers] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan Tolksdorf <b>Opened:</b> 2008-02-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.eng.mers">issues</a> in [rand.eng.mers].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -TR1 5.1.4.2 [tr.rand.eng.mers](10) requires that <tt>operator==</tt> for the <tt>mersenne_twister</tt> -returns <tt>true</tt> if and only if the states of two <tt>mersenne_twisters</tt>, -consisting each of <tt>n</tt> integers between <tt>0</tt> and <tt>2<sup>w</sup> - 1</tt>, are completely -equal. This is a contradiction with TR1 5.1.1 [tr.rand.req](3) because the given -definition of the state also includes the lower <tt>r</tt> bits of <tt>x(i-n)</tt>, which -will never be used to generate a random number. If two <tt>mersenne_twister</tt>s -only differ in the lower bits of <tt>x(i-n)</tt> they will not compare equal, -although they will produce an identical sequence of random numbers. -</p> - -<p> -26.5.3.2 [rand.eng.mers] in the latest C++ draft does not specify the behaviour -of <tt>operator==</tt> but uses a similar definition of the state and, just like -TR1 5.1.4.2 [tr.rand.eng.mers], requires the textual representation of a -<tt>mersenne_twister_engine</tt> to consist of <tt>X<sub>i-n</sub></tt> to <tt>X<sub>i-1</sub></tt>, including the -lower bits of <tt>X<sub>i-n</sub></tt>. This leads to two problems: First, the -unsuspecting implementer is likely to erroneously compare the lower <tt>r</tt> -bits of <tt>X<sub>i-n</sub></tt> in <tt>operator==</tt>. Second, if only the lower <tt>r</tt> bits differ, -two <tt>mersenne_twister_engine</tt>s will compare equal (if correctly -implemented) but have different textual representations, which -conceptually is a bit ugly. -</p> - -<p> -I propose that a paragraph or footnote is added to 26.5.3.2 [rand.eng.mers] which -clarifies that the lower <tt>r</tt> bits of <tt>X<sub>i-n</sub></tt> are not to be compared in -<tt>operator==</tt> and <tt>operator!=</tt>. It would only be consequent if furthermore -the specification for the textual respresentation was changed to -<tt>X<sub>i-n</sub> bitand ((2<sup>w</sup> - 1) - (2<sup>r</sup> - 1)), X<sub>i-(n-1)</sub>, ..., X<sub>i-1</sub></tt> or -something similar. -</p> - -<p> -These changes would likely have no practical effect, but would allow an -implementation that does the right thing to be standard-conformant. -</p> - -<p><i>[ -Bellevue: -]</i></p> - - -<blockquote> -<p> -Fermi Lab has no objection to the proposed change. However it feels that -more time is needed to check the details, which would suggest a change -to REVIEW. -</p> -<p> -Bill feels that this is NAD, not enough practical importance to abandon -the simple definition of equality, and someone would have to do a lot -more study to ensure that all cases are covered for a very small -payback. The submitter admits that "These changes would likely have no -practical effect,", and according to Plum's razor this means that it is -not worth the effort! -</p> -<p> -Revisted: Agree that the fact that there is no practical difference means that no change can be justified. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -In 26.5.3.2 [rand.eng.mers]: -</p> - -<blockquote> -<p> -Insert at the end of para 2.: -</p> - -<blockquote><p> -[<i>Note:</i> The lower <tt>r</tt> bits of <tt>X<sub>i-n</sub></tt> do not influence -the state transition and hence should not be compared when comparing two -<tt>mersenne_twister_engine</tt> objects. <i>-- end note</i>] -</p></blockquote> - -<p> -In para 5. change: -</p> - -<blockquote><p> -The textual representation of <tt>x<sub>i</sub></tt> consists of the values of -<tt>X<sub>i-n</sub> <ins>bitand ((2<sup>w</sup> - 1) - (2<sup>r</sup> - 1)), X<sub>i-(n-1)</sub></ins>, -..., X<sub>i-1</sub></tt>, in that order. -</p></blockquote> -</blockquote> - - - - - -<hr> -<h3><a name="802"></a>802. <tt>knuth_b</tt> returns wrong value</h3> -<p><b>Section:</b> 26.5.5 [rand.predef] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2008-02-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.predef">issues</a> in [rand.predef].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The 10,000<sup>th</sup> value returned by <tt>knuth_b</tt> is supposed to be -1112339016. We get 2126698284. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 26.5.5 [rand.predef]/p8: -</p> - -<blockquote> -<pre> -typedef shuffle_order_engine<minstd_rand0, 256> - knuth_b; -</pre> -<blockquote><p> -<i>Required behavior:</i> The 10000<sup>th</sup> consecutive invocation of a default-constructed -object of type <tt>knuth_b</tt> shall produce the value -<del>1112339016</del> <ins>2126698284</ins>. -</p></blockquote> -</blockquote> - - -<p><i>[ -Bellevue: Submitter withdraws defect. "We got the wrong value for entirely the right reasons". NAD. -]</i></p> - - - - - -<hr> -<h3><a name="812"></a>812. unsolicited multithreading considered harmful?</h3> -<p><b>Section:</b> 25.4.1 [alg.sort] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Paul McKenney <b>Opened:</b> 2008-02-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Multi-threading is a good thing, but unsolicited multi-threading can -potentially be harmful. For example, <tt>sort()</tt> performance might be -greatly increased via a multithreaded implementation. However, such -a multithreaded implementation could result in concurrent invocations -of the user-supplied comparator. This would in turn result in problems -given a caching comparator that might be written for complex sort keys. -Please note that this is not a theoretical issue, as multithreaded -implementations of <tt>sort()</tt> already exist. -</p> -<p> -Having a multithreaded <tt>sort()</tt> available is good, but it should not -be the default for programs that are not explicitly multithreaded. -Users should not be forced to deal with concurrency unless they have -asked for it. -</p> - -<p><i>[ -This may be covered by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2410.html">N2410</a> -Thread-Safety in the Standard Library (Rev 1). -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p><p> -This is already covered by 17.6.5.6/20 in N2723. -</p> - - - - -<hr> -<h3><a name="822"></a>822. Object with explicit copy constructor no longer <tt>CopyConstructible</tt></h3> -<p><b>Section:</b> 17.6.3.1 [utility.arg.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> James Kanze <b>Opened:</b> 2008-04-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#utility.arg.requirements">issues</a> in [utility.arg.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I just noticed that the following program is legal in C++03, but -is forbidden in the current draft: -</p> - -<blockquote><pre> -#include <vector> -#include <iostream> - -class Toto -{ -public: - Toto() {} - explicit Toto( Toto const& ) {} -} ; - -int -main() -{ - std::vector< Toto > v( 10 ) ; - return 0 ; -} -</pre></blockquote> - -<p> -Is this change intentional? (And if so, what is the -justification? I wouldn't call such code good, but I don't see -any reason to break it unless we get something else in return.) -</p> - -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote><p> -The subgroup that looked at this felt this was a good change, but it may -already be handled by incoming concepts (we're not sure). -</p></blockquote> - -<p><i>[ -Post Summit: -]</i></p> - - -<blockquote> -<p> -Alisdair: Proposed resolution kinda funky as these tables no longer -exist. Move from direct init to copy init. Clarify with Doug, recommends -NAD. -</p> -<p> -Walter: Suggest NAD via introduction of concepts. -</p> -<p> -Recommend close as NAD. -</p> -</blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Need to look at again without concepts. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote> -<p> -Move to Ready with original proposed resolution. -</p> -<p><i>[Howard: Original proposed resolution restored.]</i></p> - -</blockquote> - -<p><i>[ -2010-11 Batavia: -]</i></p> - -<p> -This issue was re-reviewed in relation to [another issue, number to follow], -and the verdict was reversed. Explicit copy and move constructors are rare -beasts, and the ripple effect of this fix was far more difficult to contain -than simply saying such types do not satisfy the <tt>MoveConstructible</tt> -and <tt>CopyConstructible</tt> requirements. -</p> - -<blockquote> -<p> -In 17.6.3.1 [utility.arg.requirements] change Table 33: <tt>MoveConstructible</tt> requirements [moveconstructible]: -</p> - -<blockquote> -<table border="1"> -<tr> -<th>expression</th><th>post-condition</th> -</tr> -<tr> -<td><tt>T t<ins>(rv)</ins><del> = rv</del></tt></td><td><tt>t</tt> is equivalent to the value of <tt>rv</tt> before the construction</td> -</tr> -<tr> -<td colspan="2" align="center">...</td> -</tr> -</table> -</blockquote> - -<p> -In 17.6.3.1 [utility.arg.requirements] change Table 34: <tt>CopyConstructible</tt> requirements [copyconstructible]: -</p> - -<blockquote> -<table border="1"> -<tr> -<th>expression</th><th>post-condition</th> -</tr> -<tr> -<td><tt>T t<ins>(u)</ins><del> = u</del></tt></td><td>the value of <tt>u</tt> is unchanged and is equivalent to <tt>t</tt></td> -</tr> -<tr> -<td colspan="2" align="center">...</td> -</tr> -</table> -</blockquote> - -</blockquote> - - - -<p><b>Proposed resolution:</b></p><p> -Resolved by <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3215.htm">n3215</a>. -</p> - - - - -<hr> -<h3><a name="826"></a>826. Equivalent of <tt>%'d</tt>, or rather, lack thereof?</h3> -<p><b>Section:</b> 22.4.2.2 [locale.nm.put] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Peter Dimov <b>Opened:</b> 2008-04-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In the spirit of <tt>printf vs iostream</tt>... -</p> - -<p> -POSIX <tt>printf</tt> says that <tt>%'d</tt> should insert grouping characters (and the -implication is that in the absence of <tt>'</tt> no grouping characters are -inserted). The <tt>num_put</tt> facet, on the other hand, seems to always insert -grouping characters. Can this be considered a defect worth fixing for -C++0x? Maybe <tt>ios_base</tt> needs an additional flag? -</p> - -<p><i>[ -Pablo Halpern: -]</i></p> - - -<blockquote><p> -I'm not sure it constitutes a defect, but I would be in favor of adding -another flag (and corresponding manipulator). -</p></blockquote> - -<p><i>[ -Martin Sebor: -]</i></p> - - -<blockquote><p> -I don't know if it qualifies as a defect but I agree that there -should be an easy way to control whether the thousands separator -should or shouldn't be inserted. A new flag would be in line with -the current design of iostreams (like <tt>boolalpha</tt>, <tt>showpos</tt>, or -<tt>showbase</tt>). -</p></blockquote> - -<p><i>[ -Sophia Antipolis: -]</i></p> - - -<blockquote><p> -This is not a part of C99. LWG suggests submitting a paper may be appropriate. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="830"></a>830. Incomplete list of char_traits specializations</h3> -<p><b>Section:</b> 21.2 [char.traits] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Dietmar Kühl <b>Opened:</b> 2008-04-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#char.traits">issues</a> in [char.traits].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> - Paragraph 4 of 21.2 [char.traits] mentions that this - section specifies two specializations (<code>char_traits<char></code> - and (<code>char_traits<wchar_t></code>). However, there are actually - four specializations provided, i.e. in addition to the two above also - <code>char_traits<char16_t></code> and <code>char_traits<char32_t></code>). - I guess this was just an oversight and there is nothing wrong with just - fixing this. -</p> - -<p><i>[ -Alisdair adds: -]</i></p> - -<blockquote><p> -<tt>char_traits< char16/32_t ></tt> -should also be added to <tt><ios_fwd></tt> in 27.3 [iostream.forward], and all the specializations -taking a <tt>char_traits</tt> parameter in that header. -</p></blockquote> - -<p><i>[ -Sophia Antipolis: -]</i></p> - - -<blockquote> -<p> -Idea of the issue is ok. -</p> -<p> -Alisdair to provide wording, once that wording arrives, move to review. -</p> - -</blockquote> - -<p><i>[ -2009-05-04 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -The main point of the issue was resolved editorially in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2723.pdf">N2723</a>, -so we are -close to NAD Editorial. -However, exploring the issue we found a second tweak was necessary for -<tt><iosfwd></tt> and that is still outstanding, so here are the words I am long -overdue delivering: -</p> - -<p><i>[ -Howard: I've put Alisdair's words into the proposed wording section and -moved the issue to Review. -]</i></p> - - -</blockquote> - -<p><i>[ -Original proposed wording. -]</i></p> - - -<blockquote> - -<p> - Replace paragraph 4 of 21.2 [char.traits] by: -</p> -<blockquote> -<p> - This subclause specifies a struct template, <code>char_traits<charT></code>, - and four explicit specializations of it, <code>char_traits<char></code>, - <code>char_traits<char16_t></code>, <code>char_traits<char32_t></code>, and - <code>char_traits<wchar_t></code>, all of which appear in the header - <string> and satisfy the requirements below. -</p> -</blockquote> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree. Move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change Forward declarations 27.3 [iostream.forward]: -</p> - -<blockquote> -<p> -<b>Header <tt><iosfwd></tt> synopsis</b> -</p> -<pre> -namespace std { - template<class charT> class char_traits; - template<> class char_traits<char>; - <ins>template<> class char_traits<char16_t>;</ins> - <ins>template<> class char_traits<char32_t>;</ins> - template<> class char_traits<wchar_t>; -... -} -</pre> -</blockquote> - - - - - -<hr> -<h3><a name="831"></a>831. wrong type for not_eof()</h3> -<p><b>Section:</b> 21.2.3 [char.traits.specializations] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Dietmar Kühl <b>Opened:</b> 2008-04-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#char.traits.specializations">issues</a> in [char.traits.specializations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> - In Table 56 (Traits requirements) the <tt>not_eof()</tt> member function - is using an argument of type <i>e</i> which denotes an object of - type <code>X::int_type</code>. However, the specializations in - 21.2.3 [char.traits.specializations] all use <code>char_type</code>. - This would effectively mean that the argument type actually can't - represent EOF in the first place. I'm pretty sure that the type used - to be <code>int_type</code> which is quite obviously the only sensible - argument. -</p> -<p> - This issue is close to being editorial. I suspect that the proposal - changing this section to include the specializations for <code>char16_t</code> - and <code>char32_t</code> accidentally used the wrong type. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> - In 21.2.3.1 [char.traits.specializations.char], - 21.2.3.2 [char.traits.specializations.char16_t], - 21.2.3.3 [char.traits.specializations.char32_t], and - [char.traits.specializations.wchar_t] correct the - argument type from <code>char_type</code> to <code>int_type</code>. -</p> - - -<p><b>Rationale:</b></p><p> -Already fixed in WP. -</p> - - - - -<hr> -<h3><a name="832"></a>832. Applying constexpr to System error support</h3> -<p><b>Section:</b> 19.5 [syserr] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2008-05-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#syserr">issues</a> in [syserr].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Initialization of objects of class <tt>error_code</tt> -(19.5.2 [syserr.errcode]) and class -<tt>error_condition</tt> (19.5.3 [syserr.errcondition]) can be made simpler and more reliable by use of -the new <tt>constexpr</tt> feature -[<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2349.pdf">N2349</a>] -of C++0x. Less code will need to be -generated for both library implementations and user programs when -manipulating constant objects of these types. -</p> - -<p> -This was not proposed originally because the constant expressions -proposal was moving into the standard at about the same time as the -Diagnostics Enhancements proposal -[<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2241.html">N2241</a>], -and it wasn't desirable to -make the later depend on the former. There were also technical concerns -as to how <tt>constexpr</tt> would apply to references. Those concerns are now -resolved; <tt>constexpr</tt> can't be used for references, and that fact is -reflected in the proposed resolution. -</p> - -<p> -Thanks to Jens Maurer, Gabriel Dos Reis, and Bjarne Stroustrup for clarification of <tt>constexpr</tt> requirements. -</p> - -<p> -LWG issue <a href="lwg-defects.html#804">804</a> is related in that it raises the question of whether the -exposition only member <tt>cat_</tt> of class <tt>error_code</tt> (19.5.2 [syserr.errcode]) and class -<tt>error_condition</tt> (19.5.3 [syserr.errcondition]) should be presented as a reference or pointer. -While in the context of <a href="lwg-defects.html#804">804</a> that is arguably an editorial question, -presenting it as a pointer becomes more or less required with this -proposal, given <tt>constexpr</tt> does not play well with references. The -proposed resolution thus changes the private member to a pointer, which -also brings it in sync with real implementations. -</p> - -<p><i>[ -Sophia Antipolis: -]</i></p> - - -<blockquote><p> -On going question of extern pointer vs. inline functions for interface. -</p></blockquote> - -<p><i>[ -Pre-San Francisco: -]</i></p> - - -<blockquote> -<p> -Beman Dawes reports that this proposal is unimplementable, and thus NAD. -</p> -<p> -Implementation would require <tt>constexpr</tt> objects of classes derived -from class <tt>error_category</tt>, which has virtual functions, and that is -not allowed by the core language. This was determined when trying to -implement the proposal using a constexpr enabled compiler provided -by Gabriel Dos Reis, and subsequently verified in discussions with -Gabriel and Jens Maurer. -</p> - -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -The proposed wording assumes the LWG <a href="lwg-defects.html#805">805</a> proposed wording has been -applied to the WP, resulting in the former <tt>posix_category</tt> being renamed -<tt>generic_category</tt>. If <a href="lwg-defects.html#805">805</a> has not been applied, the names in this -proposal must be adjusted accordingly. -</p> - -<p> -Change 19.5.1.1 [syserr.errcat.overview] Class -<tt>error_category</tt> overview <tt>error_category</tt> synopsis as -indicated: -</p> - -<blockquote><pre> -<del>const error_category& get_generic_category();</del> -<del>const error_category& get_system_category();</del> - -<del>static</del> <ins>extern</ins> const error_category<del>&</del><ins>* const</ins> generic_category<del> = get_generic_category()</del>; -<del>static</del> <ins>extern</ins> const error_category<del>&</del><ins>* const</ins> <del>native_category</del> system_category<del> = get_system_category()</del>; -</pre></blockquote> - -<p> -Change 19.5.1.5 [syserr.errcat.objects] Error category objects as indicated: -</p> - -<blockquote> -<pre> -<ins>extern</ins> const error_category<del>&</del><ins>* const</ins> <del>get_</del>generic_category<del>()</del>; -</pre> -<p> -<del><i>Returns:</i> A reference</del> <ins><tt>generic_category</tt> shall point</ins> -to <del>an</del> <ins>a statically initialized</ins> object of a type derived from -class <tt>error_category</tt>. -</p> - -<p> -<del><i>Remarks:</i></del> The object's <tt>default_error_condition</tt> and <tt>equivalent</tt> virtual -functions shall behave as specified for the class <tt>error_category</tt>. The -object's <tt>name</tt> virtual function shall return a pointer to the string -<tt>"GENERIC"</tt>. -</p> - -<pre> -<ins>extern</ins> const error_category<del>&</del><ins>* const</ins> <del>get_</del>system_category<del>()</del>; -</pre> - -<p> -<del><i>Returns:</i> A reference</del> <ins><tt>system_category</tt> shall point</ins> -to <del>an</del> <ins>a statically -initialized</ins> object of a type derived from class <tt>error_category</tt>. -</p> - -<p> -<del><i>Remarks:</i></del> The object's <tt>equivalent</tt> virtual functions shall behave as -specified for class <tt>error_category</tt>. The object's <tt>name</tt> virtual function -shall return a pointer to the string <tt>"system"</tt>. The object's -<tt>default_error_condition</tt> virtual function shall behave as follows: -</p> - -<p> -If the argument <tt>ev</tt> corresponds to a POSIX <tt>errno</tt> value <tt>posv</tt>, the function -shall return <tt>error_condition(posv, generic_category)</tt>. Otherwise, the -function shall return <tt>error_condition(ev, system_category)</tt>. What -constitutes correspondence for any given operating system is -unspecified. [<i>Note:</i> The number of potential system error codes is large -and unbounded, and some may not correspond to any POSIX <tt>errno</tt> value. -Thus implementations are given latitude in determining correspondence. -<i>-- end note</i>] -</p> -</blockquote> - -<p> -Change 19.5.2.1 [syserr.errcode.overview] Class <tt>error_code</tt> overview as indicated: -</p> - -<blockquote><pre> -class error_code { -public: - ...; - <ins>constexpr</ins> error_code(int val, const error_category<del>&</del><ins>*</ins> cat); - ... - void assign(int val, const error_category<del>&</del><ins>*</ins> cat); - ... - const error_category<del>&</del><ins>*</ins> category() const; - ... -private: - int val_; // exposition only - const error_category<del>&</del><ins>*</ins> cat_; // exposition only -</pre></blockquote> - -<p> -Change 19.5.2.2 [syserr.errcode.constructors] Class <tt>error_code</tt> constructors as indicated: -</p> - -<blockquote> -<pre> -<ins>constexpr</ins> error_code(int val, const error_category<del>&</del><ins>*</ins> cat); -</pre> -<p> -<i>Effects:</i> Constructs an object of type <tt>error_code</tt>. -</p> -<p> -<i>Postconditions:</i> <tt>val_ == val</tt> and <tt>cat_ == cat</tt>. -</p> -<p> -<i>Throws:</i> Nothing. -</p> -</blockquote> - -<p> -Change 19.5.2.3 [syserr.errcode.modifiers] Class <tt>error_code</tt> modifiers as indicated: -</p> - -<blockquote> -<pre> -void assign(int val, const error_category<del>&</del><ins>*</ins> cat); -</pre> -<p> -<i>Postconditions:</i> <tt>val_ == val</tt> and <tt>cat_ == cat</tt>. -</p> -<p> -<i>Throws:</i> Nothing. -</p> -</blockquote> - -<p> -Change 19.5.2.4 [syserr.errcode.observers] Class <tt>error_code</tt> observers as indicated: -</p> - -<blockquote> -<pre> -const error_category<del>&</del><ins>*</ins> category() const; -</pre> - -<p> -<i>Returns:</i> <tt>cat_</tt>. -</p> -<p> -<i>Throws:</i> Nothing. -</p> -</blockquote> - -<p> -Change 19.5.3.1 [syserr.errcondition.overview] Class <tt>error_condition</tt> overview as indicated: -</p> - -<blockquote> -<pre> -class error_condition { -public: - ...; - <ins>constexpr</ins> error_condition(int val, const error_category<del>&</del><ins>*</ins> cat); - ... - void assign(int val, const error_category<del>&</del><ins>*</ins> cat); - ... - const error_category<del>&</del><ins>*</ins> category() const; - ... -private: - int val_; // exposition only - const error_category<del>&</del><ins>*</ins> cat_; // exposition only -</pre> -</blockquote> - -<p> -Change 19.5.3.2 [syserr.errcondition.constructors] Class <tt>error_condition</tt> constructors as indicated: -</p> - -<blockquote> -<pre> -<ins>constexpr</ins> error_condition(int val, const error_category<del>&</del><ins>*</ins> cat); -</pre> -<p> -<i>Effects:</i> Constructs an object of type <tt>error_condition</tt>. -</p> -<p> -<i>Postconditions:</i> <tt>val_ == val</tt> and <tt>cat_ == cat</tt>. -</p> -<p> -<i>Throws:</i> Nothing. -</p> -</blockquote> - -<p> -Change 19.5.3.3 [syserr.errcondition.modifiers] Class <tt>error_condition</tt> modifiers as indicated: -</p> - -<blockquote> -<pre> -void assign(int val, const error_category<del>&</del><ins>*</ins> cat); -</pre> -<p> -<i>Postconditions:</i> <tt>val_ == val</tt> and <tt>cat_ == cat</tt>. -</p> -<p> -<i>Throws:</i> Nothing. -</p> -</blockquote> - -<p> -Change 19.5.3.4 [syserr.errcondition.observers] Class <tt>error_condition</tt> observers as indicated: -</p> - -<blockquote> -<pre> -const error_category<del>&</del><ins>*</ins> category() const; -</pre> -<p> -<i>Returns:</i> <tt>cat_</tt>. -</p> -<p> -<i>Throws:</i> Nothing. -</p> -</blockquote> - -<p> -Throughout 19.5 [syserr] System error support, change "<tt>category().</tt>" to "<tt>category()-></tt>". -Appears approximately six times. -</p> - -<p> -<i>[Partially Editorial]</i> In 19.5.4 [syserr.compare] Comparison operators, -paragraphs 2 and 4, change "<tt>category.equivalent(</tt>" to -"<tt>category()->equivalent(</tt>". -</p> - -<p> -Change 19.5.6.1 [syserr.syserr.overview] Class system_error overview as indicated: -</p> - -<blockquote><pre> -public: - system_error(error_code ec, const string& what_arg); - system_error(error_code ec); - system_error(int ev, const error_category<del>&</del><ins>*</ins> ecat, - const string& what_arg); - system_error(int ev, const error_category<del>&</del><ins>*</ins> ecat); -</pre></blockquote> - -<p> -Change 19.5.6.2 [syserr.syserr.members] Class system_error members as indicated: -</p> - -<blockquote> -<pre> -system_error(int ev, const error_category<del>&</del><ins>*</ins> ecat, const string& what_arg); -</pre> -<blockquote> -<p> -<i>Effects:</i> Constructs an object of class <tt>system_error</tt>. -</p> -<p> -<i>Postconditions:</i> <tt>code() == error_code(ev, ecat)</tt> and -<tt>strcmp(runtime_error::what(), what_arg.c_str()) == 0</tt>. -</p> -</blockquote> - -<pre> -system_error(int ev, const error_category<del>&</del><ins>*</ins> ecat); -</pre> -<blockquote> -<p> -<i>Effects:</i> Constructs an object of class <tt>system_error</tt>. -</p> -<p> -<i>Postconditions:</i> <tt>code() == error_code(ev, ecat)</tt> and -<tt>strcmp(runtime_error::what(), "") == 0</tt>. -</p> -</blockquote> -</blockquote> - - - -<p><b>Rationale:</b></p> -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote><p> -NAD because Beman said so. -</p></blockquote> - - - - - -<hr> -<h3><a name="833"></a>833. Freestanding implementations header list needs review for C++0x</h3> -<p><b>Section:</b> 17.6.1.3 [compliance] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2008-05-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#compliance">issues</a> in [compliance].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Once the C++0x standard library is feature complete, the LWG needs to -review 17.6.1.3 [compliance] Freestanding implementations header list to -ensure it reflects LWG consensus. -</p> - -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote> -<p> -This is a placeholder defect to remind us to review the table once we've -stopped adding headers to the library. -</p> -<p> -Three new headers that need to be added to the list: -</p> -<blockquote><pre> -<initializer_list> <concept> <iterator_concepts> -</pre></blockquote> -<p> -<tt><iterator_concepts></tt>, in particular, has lots of stuff -that isn't needed, so maybe the stuff that is needed should be broken -out into a separate header. -</p> -<p> -Robert: What about <tt>reference_closure</tt>? It's currently in -<tt><functional></tt>. -</p> -</blockquote> - -<p><i>[ -Post Summit Daniel adds: -]</i></p> - - -<blockquote> -<ol> -<li> -The comment regarding <tt>reference_closure</tt> seems moot since it was just -recently decided to remove that. -</li> -<li> -A reference to proposal -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2814.pdf">N2814</a> -("Fixing freestanding") should be added. This -paper e.g. proposes to add only <tt><initializer_list></tt> to the include list -of freestanding. -</li> -</ol> -</blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote> -<p> -Addressed by paper -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2814.pdf">N2814</a>. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="837"></a>837. - <code>basic_ios::copyfmt()</code> overly loosely specified - </h3> -<p><b>Section:</b> 27.5.5.3 [basic.ios.members] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2008-05-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#basic.ios.members">issues</a> in [basic.ios.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - <p> - -The <code>basic_ios::copyfmt()</code> member function is specified in 27.5.5.3 [basic.ios.members] to have the following effects: - - </p> - <blockquote><p> - -<i>Effects</i>: If <code>(this == &rhs)</code> does -nothing. Otherwise assigns to the member objects of <code>*this</code> -the corresponding member objects of <code>rhs</code>, except that -</p> - <ul> - <li> - -<code>rdstate()</code> and <code>rdbuf()</code> are left unchanged; - - </li> - <li> - -<code>exceptions()</code> is altered last by -calling <code>exceptions(rhs.except)</code> - - </li> - <li> - -the contents of arrays pointed at by <code>pword</code> -and <code>iword</code> are copied not the pointers themselves - - </li> - </ul> - </blockquote> - <p> - -Since the rest of the text doesn't specify what the member objects -of <code>basic_ios</code> are this seems a little too loose. - -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the proposed resolution. -Move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> - -I propose to tighten things up by adding a <i>Postcondition</i> clause -to the function like so: - - </p> - <blockquote><p> - <i>Postconditions:</i> - </p> - <table border="1"> - <thead> - <tr> - <th colspan="2"><code>copyfmt()</code> postconditions</th> - </tr> - <tr> - <th>Element</th> - <th>Value</th> - </tr> - </thead> - <tbody> - <tr> - <td><code>rdbuf()</code></td> - <td><i>unchanged</i></td> - </tr> - <tr> - <td><code>tie()</code></td> - <td><code>rhs.tie()</code></td> - </tr> - <tr> - <td><code>rdstate()</code></td> - <td><i>unchanged</i></td> - </tr> - <tr> - <td><code>exceptions()</code></td> - <td><code>rhs.exceptions()</code></td> - </tr> - <tr> - <td><code>flags()</code></td> - <td><code>rhs.flags()</code></td> - </tr> - <tr> - <td><code>width()</code></td> - <td><code>rhs.width()</code></td> - </tr> - <tr> - <td><code>precision()</code></td> - <td><code>rhs.precision()</code></td> - </tr> - <tr> - <td><code>fill()</code></td> - <td><code>rhs.fill()</code></td> - </tr> - <tr> - <td><code>getloc()</code></td> - <td><code>rhs.getloc()</code></td> - </tr> - </tbody> - </table> - </blockquote> - <p> - -The format of the table follows Table 117 (as -of <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2588.pdf">N2588</a>): <code>basic_ios::init()</code> -effects. - - </p> - <p> - -The intent of the new table is not to impose any new requirements or -change existing ones, just to be more explicit about what I believe is -already there. - - </p> - - - - -<hr> -<h3><a name="840"></a>840. <tt>pair</tt> default template argument</h3> -<p><b>Section:</b> 20.3 [pairs] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thorsten Ottosen <b>Opened:</b> 2008-05-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#pairs">issues</a> in [pairs].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I have one issue with <tt>std::pair</tt>. Well, it might just be a very annoying -historical accident, but why is there no default template argument for -the second template argument? This is so annoying when the type in -question is looong and hard to write (type deduction with <tt>auto</tt> won't -help those cases where we use it as a return or argument type). -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change the synopsis in 20.2 [utility] to read: -</p> - -<blockquote><pre> -template <class T1, class T2 <ins>= T1</ins>> struct pair; -</pre></blockquote> - -<p> -Change 20.3 [pairs] to read: -</p> - -<blockquote><pre> -namespace std { - template <class T1, class T2 <ins>= T1</ins>> - struct pair { - typedef T1 first_type; - typedef T2 second_type; - ... -</pre></blockquote> - - -<p><b>Rationale:</b></p><p> -<tt>std::pair</tt> is a heterogeneous container. -</p> - - - - -<hr> -<h3><a name="841"></a>841. cstdint.syn inconsistent with C99</h3> -<p><b>Section:</b> 18.4.1 [cstdint.syn] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2008-05-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#cstdint.syn">issues</a> in [cstdint.syn].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - <p> - -In specifying the names of macros and types defined in -header <code><stdint.h></code>, C99 makes use of the -symbol <code><i>N</i></code> to accommodate unusual platforms with -word sizes that aren't powers of two. C99 -permits <code><i>N</i></code> to take on any positive integer value -(including, for example, 24). - - </p> - <p> - -In cstdint.syn Header <code><cstdint></code> -synopsis, C++ on the other hand, fixes the value -of <code><i>N</i></code> to 8, 16, 32, and 64, and specifies only -types with these exact widths. - - </p> - <p> - -In addition, paragraph 1 of the same section makes use of a rather -informal shorthand notation to specify sets of macros. When -interpreted strictly, the notation specifies macros such -as <code>INT_8_MIN</code> that are not intended to be specified. - - </p> - <p> - -Finally, the section is missing the usual table of symbols defined -in that header, making it inconsistent with the rest of the -specification. - - </p> - - <p><b>Proposed resolution:</b></p> - <p> - -I propose to use the same approach in the C++ spec as C99 uses, that -is, to specify the header synopsis in terms of "exposition only" types -that make use of the symbol <code><i>N</i></code> to denote one or -more of a theoretically unbounded set of widths. - - </p> - <p> - -Further, I propose to add a new table to section listing the symbols -defined in the header using a more formal notation that avoids -introducing inconsistencies. - - </p> - <p> - -To this effect, in cstdint.syn -Header <code><cstdint></code> synopsis, replace both the -synopsis and paragraph 1 with the following text: - - </p> - <blockquote> - <p> - </p> - <ol> - <li> - -In the names defined in the <code><cstdint></code> header, the -symbol <code><i>N</i></code> represents a positive decimal integer -with no leading zeros (e.g., 8 or 24, but not 0, 04, or 048). With the -exception of exact-width types, macros and types for values -of <code><i>N</i></code> in the set of 8, 16, 32, and 64 are -required. Exact-width types, and any macros and types for values -of <code><i>N</i></code> other than 8, 16, 32, and 64 are -optional. However, if an implementation provides integer types with -widths of 8, 16, 32, or 64 bits, the corresponding exact-width types -and macros are required. - - </li> - </ol> - <pre> -namespace std { - - // required types - - // Fastest minimum-width integer types - typedef <i>signed integer type</i> int_fast8_t; - typedef <i>signed integer type</i> int_fast16_t; - typedef <i>signed integer type</i> int_fast32_t; - typedef <i>signed integer type</i> int_fast64_t; - - typedef <i>unsigned integer type</i> uint_fast8_t; - typedef <i>unsigned integer type</i> uint_fast16_t; - typedef <i>unsigned integer type</i> uint_fast32_t; - typedef <i>unsigned integer type</i> uint_fast64_t; - - // Minimum-width integer types - typedef <i>signed integer type</i> int_least8_t; - typedef <i>signed integer type</i> int_least16_t; - typedef <i>signed integer type</i> int_least32_t; - typedef <i>signed integer type</i> int_least64_t; - - typedef <i>unsigned integer type</i> uint_least8_t; - typedef <i>unsigned integer type</i> uint_least16_t; - typedef <i>unsigned integer type</i> uint_least32_t; - typedef <i>unsigned integer type</i> uint_least64_t; - - // Greatest-width integer types - typedef <i>signed integer type</i> intmax_t; - typedef <i>unsigned integer type</i> uintmax_t; - - // optionally defined types - - // Exact-width integer types - typedef <i>signed integer type</i> int<i>N</i>_t; - typedef <i>unsigned integer type</i> uint<i>N</i>_t; - - // Fastest minimum-width integer types for values - // of <i>N</i> other than 8, 16, 32, and 64 - typedef <i>signed integer type</i> uint_fast<i>N</i>_t; - typedef <i>unsigned integer type</i> uint_fast<i>N</i>_t; - - // Minimum-width integer types for values - // of <i>N</i> other than 8, 16, 32, and 64 - typedef <i>signed integer type</i> uint_least<i>N</i>_t; - typedef <i>unsigned integer type</i> uint_least<i>N</i>_t; - - // Integer types capable of holding object pointers - typedef <i>signed integer type</i> intptr_t; - typedef <i>signed integer type</i> intptr_t; - -}</pre> - </blockquote> - <p> - -[Note to editor: Remove all of the existing paragraph 1 from cstdint.syn.] - - </p> - <blockquote><p> - Table ??: Header <code><cstdint></code> synopsis - </p> - <table border="1"> - <thead> - <tr> - <th>Type</th> - <th colspan="3">Name(s)</th> - </tr> - </thead> - <tbody> - <tr> - <td rowspan="11"><b>Macros:</b></td> - <td><tt>INT<i>N</i>_MIN</tt></td> - <td><tt>INT<i>N</i>_MAX</tt></td> - <td><tt>UINT<i>N</i>_MAX</tt></td> - </tr> - <tr> - <td><tt>INT_FAST<i>N</i>_MIN</tt></td> - <td><tt>INT_FAST<i>N</i>_MAX</tt></td> - <td><tt>UINT_FAST<i>N</i>_MAX</tt></td> - </tr> - <tr> - <td><tt>INT_LEAST<i>N</i>_MIN</tt></td> - <td><tt>INT_LEAST<i>N</i>_MAX</tt></td> - <td><tt>UINT_LEAST<i>N</i>_MAX</tt></td> - </tr> - <tr> - <td><tt>INTPTR_MIN</tt></td> - <td><tt>INTPTR_MAX</tt></td> - <td><tt>UINTPTR_MAX</tt></td> - </tr> - <tr> - <td><tt>INTMAX_MIN</tt></td> - <td><tt>INTMAX_MAX</tt></td> - <td><tt>UINTMAX_MAX</tt></td> - </tr> - <tr> - <td><tt>PTRDIFF_MIN</tt></td> - <td><tt>PTRDIFF_MAX</tt></td> - <td><tt>PTRDIFF_MAX</tt></td> - </tr> - <tr> - <td><tt>SIG_ATOMIC_MIN</tt></td> - <td><tt>SIG_ATOMIC_MAX</tt></td> - <td><tt>SIZE_MAX</tt></td> - </tr> - <tr> - <td><tt>WCHAR_MIN</tt></td> - <td><tt>WCHAR_MAX</tt></td> - <td></td> - </tr> - <tr> - <td><tt>WINT_MIN</tt></td> - <td><tt>WINT_MAX</tt></td> - <td></td> - </tr> - <tr> - <td><tt>INT<i>N</i>_C()</tt></td> - <td><tt>UINT<i>N</i>_C()</tt></td> - <td></td> - </tr> - <tr> - <td><tt>INTMAX_C()</tt></td> - <td><tt>UINTMAX_C()</tt></td> - <td></td> - </tr> - <tr> - <td rowspan="5"><b>Types:</b></td> - <td><tt>int<i>N</i>_t</tt></td> - <td><tt>uint<i>N</i>_t</tt></td> - <td></td> - </tr> - <tr> - <td><tt>int_fast<i>N</i>_t</tt></td> - <td><tt>uint_fast<i>N</i>_t</tt></td> - <td></td> - </tr> - <tr> - <td><tt>int_least<i>N</i>_t</tt></td> - <td><tt>uint_least<i>N</i>_t</tt></td> - <td></td> - </tr> - <tr> - <td><tt>intptr_t</tt></td> - <td><tt>uintptr_t</tt></td> - <td></td> - </tr> - <tr> - <td><tt>intmax_t</tt></td> - <td><tt>uintmax_t</tt></td> - <td></td> - </tr> - </tbody> - </table> - </blockquote> - - - - - -<hr> -<h3><a name="849"></a>849. missing type traits to compute root class and derived class of types in a class hierachy</h3> -<p><b>Section:</b> 20.10.7.6 [meta.trans.other] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thorsten Ottosen <b>Opened:</b> 2008-06-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#meta.trans.other">active issues</a> in [meta.trans.other].</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.trans.other">issues</a> in [meta.trans.other].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The type traits library contains various traits to dealt with -polymorphic types, e.g. <tt>std::has_virtual_destructor</tt>, <tt>std::is_polymorphic</tt> -and <tt>std::is_base_of</tt>. However, there is no way to compute the unique -public base class of a type if such one exists. Such a trait could be -very useful if one needs to instantiate a specialization made for the -root class whenever a derived class is passed as parameter. For example, -imagine that you wanted to specialize <tt>std::hash</tt> for a class -hierarchy---instead of specializing each class, you could specialize the -<tt>std::hash<root_class></tt> and provide a partial specialization that worked -for all derived classes. -</p> - -<p> -This ability---to specify operations in terms of their equivalent in the -root class---can be done with e.g. normal functions, but there is, -AFAIK, no way to do it for class templates. Being able to access -compile-time information about the type-hierachy can be very powerful, -and I therefore also suggest traits that computes the directly derived -class whenever that is possible. -</p> - -<p> -If the computation can not be done, the traits should fall back on an -identity transformation. I expect this gives the best overall usability. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add the following to the synopsis in 20.10.2 [meta.type.synop] under "other transformations": -</p> - -<blockquote><pre> -template< class T > struct direct_base_class; -template< class T > struct direct_derived_class; -template< class T > struct root_base_class; -</pre></blockquote> - -<p> -Add three new entries to table 51 (20.10.7.6 [meta.trans.other]) with the following content -</p> - -<blockquote> -<table border="1"> -<tr> -<th>Template</th><th>Condition</th><th>Comments</th> -</tr> -<tr> -<td><tt>template< class T > struct direct_base_class;</tt></td> -<td><tt>T</tt> shall be a complete type.</td> -<td>The member typedef <tt>type</tt> shall equal the accessible unambiguous direct base class of <tt>T</tt>. -If no such type exists, the member typedef <tt>type</tt> shall equal <tt>T</tt>.</td> -</tr> -<tr> -<td><tt>template< class T > struct direct_derived_class;</tt></td> -<td><tt>T</tt> shall be a complete type.</td> -<td>The member typedef <tt>type</tt> shall equal the unambiguous type which has <tt>T</tt> -as an accessible unambiguous direct base class. If no such type exists, the member typedef -<tt>type</tt> shall equal <tt>T</tt>.</td> -</tr> -<tr> -<td><tt>template< class T > struct root_base_class;</tt></td> -<td><tt>T</tt> shall be a complete type.</td> -<td>The member typedef <tt>type</tt> shall equal the accessible unambiguous most indirect base class of -<tt>T</tt>. If no such type exists, the member typedef type shall equal <tt>T</tt>.</td> -</tr> -</table> -</blockquote> - - - -<p><b>Rationale:</b></p><p> -2008-9-16 San Francisco: Issue pulled by author prior to being reviewed by the LWG. -</p> - - - - -<hr> -<h3><a name="855"></a>855. capacity() and reserve() for deque?</h3> -<p><b>Section:</b> 23.3.3.3 [deque.capacity] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Hervé Brönnimann <b>Opened:</b> 2008-06-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#deque.capacity">issues</a> in [deque.capacity].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The main point is that <tt>capacity</tt> can be viewed as a mechanism to -guarantee the validity of <tt>iterators</tt> when only <tt>push_back/pop_back</tt> -operations are used. For <tt>vector</tt>, this goes with reallocation. For -<tt>deque</tt>, this is a bit more subtle: <tt>capacity()</tt> of a <tt>deque</tt> may shrink, -whereas that of <tt>vector</tt> doesn't. In a circular buffer impl. of the -map, as Howard did, there is very similar notion of capacity: as long -as <tt>size()</tt> is less than <tt>B * (</tt>total size of the map <tt>- 2)</tt>, it is -guaranteed that no <tt>iterator</tt> is invalidated after any number of -<tt>push_front/back</tt> and <tt>pop_front/back</tt> operations. But this does not -hold for other implementations. -</p> -<p> -Still, I believe, <tt>capacity()</tt> can be defined by <tt>size() +</tt> how many -<tt>push_front/back</tt> minus <tt>pop_front/back</tt> that can be performed before -terators are invalidated. In a classical impl., <tt>capacity() = size() -+ </tt> the min distance to either "physical" end of the deque (i.e., -counting the empty space in the last block plus all the blocks until -the end of the map of block pointers). In Howard's circular buffer -impl., <tt>capacity() = B * (</tt>total size of the map <tt>- 2)</tt> still works with -this definition, even though the guarantee could be made stronger. -</p> -<p> -A simple picture of a deque: -</p> -<blockquote><pre> -A-----|----|-----|---F+|++++|++B--|-----|-----Z -</pre></blockquote> -<p> -(A,Z mark the beginning/end, | the block boundaries, F=front, B=back, -and - are uninitialized, + are initialized) -In that picture: <tt>capacity = size() + min(dist(A,F),dist(B,Z)) = min -(dist(A,B),dist(F,Z))</tt>. -</p> -<p> -<tt>Reserve(n)</tt> can grow the map of pointers and add possibly a number of -empty blocks to it, in order to guarantee that the next <tt>n-size() -push_back/push_front</tt> operations will not invalidate iterators, and -also will not allocate (i.e. cannot throw). The second guarantee is -not essential and can be left as a QoI. I know well enough existing -implementations of <tt>deque</tt> (sgi/stl, roguewave, stlport, and -dinkumware) to know that either can be implemented with no change to -the existing class layout and code, and only a few modifications if -blocks are pre-allocated (instead of always allocating a new block, -check if the next entry in the map of block pointers is not zero). -</p> -<p> -Due to the difference with <tt>vector</tt>, wording is crucial. Here's a -proposed wording to make things concrete; I tried to be reasonably -careful but please double-check me: -</p> - -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote> -<p> -Hans: should the Returns clause for capacity read "1 Returns: A lower -bound..." rather than "1 Returns: An upper bound..." -</p> -<p> -Howard: maybe what's needed is capacity_front and capacity_back. In -fact, I think I implemented a deque that had these members as -implementation details. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - -<p> -Add new signatures to synopsis in 23.3.3 [deque]: -</p> - -<blockquote><pre> -size_type capacity() const; -bool reserve(size_type n); -</pre></blockquote> - -<p> -Add new signatures to 23.3.3.3 [deque.capacity]: -</p> - -<blockquote> -<pre> -size_type capacity() const; -</pre> -<blockquote> -<p> -1 <i>Returns:</i> An upper bound on <tt>n + max(n_f - m_f, n_b - m_b)</tt> such -that, for any sequence of <tt>n_f push_front</tt>, <tt>m_f pop_front</tt>, <tt>n_b -push_back</tt>, and <tt>m_b pop_back</tt> operations, interleaved in any order, -starting with the current <tt>deque</tt> of size <tt>n</tt>, the <tt>deque</tt> does not -invalidate any of its iterators except to the erased elements. -</p> -<p> -2 <i>Remarks:</i> Unlike a <tt>vector</tt>'s capacity, the capacity of a <tt>deque</tt> can -decrease after a sequence of insertions at both ends, even if none of -the operations caused the <tt>deque</tt> to invalidate any of its iterators -except to the erased elements. -</p> -</blockquote> -</blockquote> - -<blockquote> -<pre> -bool reserve(size_type n); -</pre> -<blockquote> -<p> -2 <i>Effects:</i> A directive that informs a <tt>deque</tt> of a planned sequence of -<tt>push_front</tt>, <tt>pop_front</tt>, <tt>push_back</tt>, and <tt>pop_back</tt> operations, so that it -can manage iterator invalidation accordingly. After <tt>reserve()</tt>, -<tt>capacity()</tt> is greater or equal to the argument of <tt>reserve</tt> if this -operation returns <tt>true</tt>; and equal to the previous value of <tt>capacity()</tt> -otherwise. If an exception is thrown, there are no effects. -</p> -<p> -3 <i>Returns:</i> <tt>true</tt> if iterators are invalidated as a result of this -operation, and false otherwise. -</p> -<p> -4 <i>Complexity:</i> It does not change the size of the sequence and takes -at most linear time in <tt>n</tt>. -</p> -<p> -5 <i>Throws:</i> <tt>length_error</tt> if <tt>n > max_size()</tt>. -</p> -<p> -6 <i>Remarks:</i> It is guaranteed that no invalidation takes place during a -sequence of <tt>insert</tt> or <tt>erase</tt> operations at either end that happens -after a call to <tt>reserve()</tt> except to the erased elements, until the -time when an insertion would make <tt>max(n_f-m_f, n_b-m_b)</tt> larger than -<tt>capacity()</tt>, where <tt>n_f</tt> is the number of <tt>push_front</tt>, <tt>m_f</tt> of <tt>pop_front</tt>, -<tt>n_b</tt> of <tt>push_back</tt>, and <tt>m_b</tt> of <tt>pop_back</tt> operations since the call to -<tt>reserve()</tt>. -</p> -<p> -7 An implementation is free to pre-allocate buffers so as to -offer the additional guarantee that no exception will be thrown -during such a sequence other than by the element constructors. -</p> -</blockquote> -</blockquote> - -<p> -And 23.3.3.4 [deque.modifiers] para 1, can be enhanced: -</p> - -<blockquote><p> -1 <i>Effects:</i> An insertion in the middle of the deque invalidates all the iterators and references to elements of the -deque. An insertion at either end of the deque invalidates all the iterators to the deque, -<ins>unless provisions have been made with reserve,</ins> -but has no effect on the validity of references to elements of the deque. -</p></blockquote> - - -<p><b>Rationale:</b></p> -<p>Complication outweighs the benefit.</p> - - - - - -<hr> -<h3><a name="862"></a>862. Impossible complexity for 'includes'</h3> -<p><b>Section:</b> 25.4.5.1 [includes] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2008-07-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#includes">issues</a> in [includes].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In 25.4.5.1 [includes] the complexity is "at most -1 comparisons" if passed -two empty ranges. I don't know how to perform a negative number of -comparisions! -</p> - -<p> -This same issue also applies to: -</p> - -<ul> -<li><tt>set_union</tt></li> -<li><tt>set_intersection</tt></li> -<li><tt>set_difference</tt></li> -<li><tt>set_symmetric_difference</tt></li> -<li><tt>merge</tt></li> -</ul> - -<p><i>[ -2009-03-30 Beman adds: -]</i></p> - - -<blockquote><p> -Suggest NAD. The complexity of empty ranges is -1 in other places in the -standard. See 25.4.4 [alg.merge] <tt>merge</tt> and -<tt>inplace_merge</tt>, and <tt>forward_list</tt> merge, for example. -The time and effort to find and fix all places in the standard where -empty range[s] result in negative complexity isn't worth the very -limited benefit. -</p></blockquote> - -<p><i>[ -2009-05-09 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -I'm not happy with NAD if we can find a simple solution. -</p> -<p> -How about adding a rider somewhere in clause 17 suggesting that complexities -that specify a negative number of operations are treated as specifying zero -operations? That should generically solve the issue without looking for -further cases. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Pete to provide "straightforward" wording. -Move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Recommend NAD. -</p> - - - - - -<hr> -<h3><a name="863"></a>863. What is the state of a stream after close() succeeds</h3> -<p><b>Section:</b> 27.9.1 [fstreams] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Steve Clamage <b>Opened:</b> 2008-07-08 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#fstreams">issues</a> in [fstreams].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Suppose writing to an <tt>[o]fstream</tt> fails and you later close the <tt>stream</tt>. -The <tt>overflow()</tt> function is called to flush the buffer (if it exists). -Then the file is unconditionally closed, as if by calling <tt>flcose</tt>. -</p> -<p> -If either <tt>overflow</tt> or <tt>fclose</tt> fails, <tt>close()</tt> reports failure, and clearly -the <tt>stream</tt> should be in a failed or bad state. -</p> -<p> -Suppose the buffer is empty or non-existent (so that <tt>overflow()</tt> does not -fail), and <tt>fclose</tt> succeeds. The <tt>close()</tt> function reports success, but -what is the state of the <tt>stream</tt>? -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Tom's impression is that the issue is about the <tt>failbit</tt>, etc. -</p> -<p> -Bill responds that the stream is now closed, -and any status bits remain unchanged. -</p> -<p> -See the description of <tt>close()</tt> in 27.9.1.17 [fstream.members]. -</p> -<p> -We prefer not to add wording to say that nothing changes. -Move to NAD. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="864"></a>864. Defect in atomic wording</h3> -<p><b>Section:</b> 29.6 [atomics.types.operations] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Anthony Williams <b>Opened:</b> 2008-07-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.types.operations">issues</a> in [atomics.types.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -There's an error in 29.6 [atomics.types.operations]/p9: -</p> - -<blockquote> -<pre> -C atomic_load(const volatile A * object); -C atomic_load_explicit(const volatile A * object, memory_order); -C A ::load(memory_order order = memory_order_seq_cst) const volatile; -</pre> -<blockquote> -<p> -<i>Requires:</i> The <tt>order</tt> argument shall not be <tt>memory_order_acquire</tt> nor -<tt>memory_order_acq_rel</tt>. -</p> -</blockquote> -</blockquote> - -<p> -I believe that this should state -</p> -<blockquote><p> -shall not be <tt>memory_order_release</tt>. -</p></blockquote> - -<p> -There's also an error in 29.6 [atomics.types.operations]/p17: -</p> - -<blockquote><p> -... When only one <tt>memory_order</tt> argument is supplied, the value of success -is <tt>order</tt>, and -the value of failure is <tt>order</tt> except that a value of -<tt>memory_order_acq_rel</tt> shall be replaced by the value -<tt>memory_order_require</tt> ... -</p></blockquote> -<p> -I believe this should state -</p> -<blockquote><p> -shall be replaced by the value <tt>memory_order_acquire</tt> ... -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 29.6 [atomics.types.operations]/p9: -</p> - -<blockquote> -<pre> -C atomic_load(const volatile A * object); -C atomic_load_explicit(const volatile A * object, memory_order); -C A ::load(memory_order order = memory_order_seq_cst) const volatile; -</pre> -<blockquote> -<p> -<i>Requires:</i> The <tt>order</tt> argument shall not be <del><tt>memory_order_acquire</tt></del> -<ins><tt>memory_order_release</tt></ins> nor <tt>memory_order_acq_rel</tt>. -</p> -</blockquote> -</blockquote> - -<p> -Change 29.6 [atomics.types.operations]/p17: -</p> - -<blockquote><p> -... When only one <tt>memory_order</tt> argument is supplied, the value of success -is <tt>order</tt>, and -the value of failure is <tt>order</tt> except that a value of -<tt>memory_order_acq_rel</tt> shall be replaced by the value -<del><tt>memory_order_require</tt></del> <ins><tt>memory_order_acquire</tt></ins> ... -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p>Already fixed by the time the LWG processed it.</p> - - - - - -<hr> -<h3><a name="867"></a>867. Valarray and value-initialization</h3> -<p><b>Section:</b> 26.6.2.2 [valarray.cons] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alberto Ganesh Barbati <b>Opened:</b> 2008-07-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#valarray.cons">issues</a> in [valarray.cons].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -From 26.6.2.2 [valarray.cons], paragraph 2: -</p> - -<blockquote><pre> -explicit valarray(size_t); -</pre> -<blockquote><p> -The array created by this constructor has a length equal to the value of the argument. The elements -of the array are constructed using the default constructor for the instantiating type <tt>T</tt>. -</p></blockquote> -</blockquote> - -<p> -The problem is that the most obvious <tt>T</tt>s for <tt>valarray</tt> are <tt>float</tt> -and <tt>double</tt>, they don't have a default constructor. I guess the intent is to value-initialize -the elements, so I suggest replacing: -</p> - -<blockquote><p> -The elements of the array are constructed using the default constructor for the instantiating type <tt>T</tt>. -</p></blockquote> -<p> -with -</p> -<blockquote><p> -The elements of the array are value-initialized. -</p></blockquote> - -<p> -There is another reference to the default constructor of <tt>T</tt> in the non-normative note in paragraph 9. -That reference should also be replaced. (The normative wording in paragraph 8 refers to <tt>T()</tt> -and so it doesn't need changes). -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the proposed resolution. -Move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 26.6.2.2 [valarray.cons], paragraph 2: -</p> - -<blockquote> -<pre> -explicit valarray(size_t); -</pre> -<blockquote><p> -The array created by this constructor has a length equal to the value of the argument. The elements -of the array are <del>constructed using the default constructor for the instantiating type <tt>T</tt></del> -<ins>value-initialized (8.5 [dcl.init])</ins>. -</p></blockquote> -</blockquote> - -<p> -Change 26.6.2.8 [valarray.members], paragraph 9: -</p> - -<blockquote><p> -[<i>Example:</i> If the argument has the value -2, the first two elements of the result will be <del>constructed using the -default constructor</del> -<ins>value-initialized (8.5 [dcl.init])</ins>; -the third element of the result will be assigned the value of the first element of the argument; etc. <i>-- end example</i>] -</p></blockquote> - - - - - - -<hr> -<h3><a name="873"></a>873. signed integral type and unsigned integral type are not clearly defined</h3> -<p><b>Section:</b> 3.9.1 [basic.fundamental] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Travis Vitek <b>Opened:</b> 2008-06-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - <p> - Neither the term "signed integral type" nor the term "unsigned - integral type" is defined in the core language section of the - standard, therefore the library section should avoid its use. The - terms <i>signed integer type</i> and <i>unsigned integer type</i> are - indeed defined (in 3.9.1 [basic.fundamental]), thus the usages should be - replaced accordingly. - </p> - - <p> - Note that the key issue here is that "signed" + "integral type" != - "signed integral type". - - The types <code>bool</code>, <code>char</code>, <code>char16_t</code>, - <code>char32_t</code> and <code>wchar_t</code> are all listed as - integral types, but are neither of <i>signed integer type</i> or - <i>unsigned integer type</i>. According to 3.9 [basic.types] p7, a synonym for - integral type is <i>integer type</i>. - - Given this, one may choose to assume that an <i>integral type</i> that - can represent values less than zero is a <i>signed integral type</i>. - Unfortunately this can cause ambiguities. - - As an example, if <code>T</code> is <code>unsigned char</code>, the - expression <code>make_signed<T>::type</code>, is supposed to - name a signed integral type. There are potentially two types that - satisfy this requirement, namely <code>signed char</code> and - <code>char</code> (assuming <code>CHAR_MIN < 0</code>). - </p> - -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote><p> -Plum, Sebor to review. -</p></blockquote> - -<p><i>[ -Post Summit Daniel adds: -]</i></p> - - -<blockquote><p> -The proposed resolution needs to be "conceptualized". Currently we have -in [concept.support] only concept <tt>IntegralType</tt> -for all "integral types", thus indeed the current <tt>Container</tt> -concept and Iterator concepts are sufficiently satisfied with "integral -types". If the changes are applied, we might ask core for concept -<tt>BilateralIntegerType</tt> and add proper restrictions to the library -concepts. -</p></blockquote> - - - - <p><b>Proposed resolution:</b></p> - <p> - I propose to use the terms "signed integer type" and "unsigned integer - type" in place of "signed integral type" and "unsigned integral type" - to eliminate such ambiguities. - </p> - - <p> - The proposed change makes it absolutely clear that the difference - between two pointers cannot be <tt>char</tt> or <tt>wchar_t</tt>, - but could be any of the signed integer types. - 5.7 [expr.add] paragraph 6... - </p> - <blockquote> - <p> - </p> - <ol> - <li> - When two pointers to elements of the same array object are - subtracted, the result is the difference of the subscripts of - the two array elements. The type of the result is an - implementation-defined <del>signed integral - type</del><ins>signed integer type</ins>; this type shall be the - same type that is defined as <code>std::ptrdiff_t</code> in the - <code><cstdint></code> header (18.1)... - </li> - </ol> - </blockquote> - - <p> - The proposed change makes it clear that <tt>X::size_type</tt> and - <tt>X::difference_type</tt> cannot be <tt>char</tt> or - <tt>wchar_t</tt>, but could be one of the signed or unsigned integer - types as appropriate. - 17.6.3.5 [allocator.requirements] table 40... - </p> - <blockquote><p> - Table 40: Allocator requirements - </p> - <table border="1"> - <thead> - <tr> - <th>expression</th> - <th>return type</th> - <th>assertion/note/pre/post-condition</th> - </tr> - </thead> - <tbody> - <tr> - <td><tt>X::size_type</tt></td> - <td> - <del>unsigned integral type</del> - <ins>unsigned integer type</ins> - </td> - <td>a type that can represent the size of the largest object in - the allocation model.</td> - </tr> - <tr> - <td><tt>X::difference_type</tt></td> - <td> - <del>signed integral type</del> - <ins>signed integer type</ins> - </td> - <td>a type that can represent the difference between any two - pointers in the allocation model.</td> - </tr> - </tbody> - </table> - </blockquote> - - <p> - The proposed change makes it clear that <tt>make_signed<T>::type</tt> - must be one of the signed integer types as defined in 3.9.1. Ditto for - <tt>make_unsigned<T>type</tt> and unsigned integer types. - 20.10.7.3 [meta.trans.sign] table 48... - </p> - <blockquote><p> - Table 48: Sign modifications - </p> - <table border="1"> - <thead> - <tr> - <th>Template</th> - <th>Comments</th> - </tr> - </thead> - <tbody> - <tr> - <td> - <tt>template <class T> struct make_signed;</tt> - </td> - <td> - If <code>T</code> names a (possibly cv-qualified) <del>signed - integral type</del><ins>signed integer type</ins> (3.9.1) then - the member typedef <code>type</code> shall name the type - <code>T</code>; otherwise, if <code>T</code> names a (possibly - cv-qualified) <del>unsigned integral type</del><ins>unsigned - integer type</ins> then <code>type</code> shall name the - corresponding <del>signed integral type</del><ins>signed - integer type</ins>, with the same cv-qualifiers as - <code>T</code>; otherwise, <code>type</code> shall name the - <del>signed integral type</del><ins>signed integer type</ins> - with the smallest rank (4.13) for which <code>sizeof(T) == - sizeof(type)</code>, with the same cv-qualifiers as - <code>T</code>. - - <i>Requires:</i> <code>T</code> shall be a (possibly - cv-qualified) integral type or enumeration but not a - <code>bool</code> type. - </td> - </tr> - <tr> - <td> - <tt>template <class T> struct make_unsigned;</tt> - </td> - <td> - If <code>T</code> names a (possibly cv-qualified) - <del>unsigned integral type</del><ins>unsigned integer - type</ins> (3.9.1) then the member typedef <code>type</code> - shall name the type <code>T</code>; otherwise, if - <code>T</code> names a (possibly cv-qualified) <del>signed - integral type</del><ins>signed integer type</ins> then - <code>type</code> shall name the corresponding <del>unsigned - integral type</del><ins>unsigned integer type</ins>, with the - same cv-qualifiers as <code>T</code>; otherwise, - <code>type</code> shall name the <del>unsigned integral - type</del><ins>unsigned integer type</ins> with the smallest - rank (4.13) for which <code>sizeof(T) == sizeof(type)</code>, - with the same cv-qualifiers as <code>T</code>. - - <i>Requires:</i> <code>T</code> shall be a (possibly - cv-qualified) integral type or enumeration but not a - <code>bool</code> type. - </td> - </tr> - </tbody> - </table> - </blockquote> - - - <p> - Note: I believe that the basefield values should probably be - prefixed with <tt>ios_base::</tt> as they are in 22.4.2.2.2 [facet.num.put.virtuals] - - The listed virtuals are all overloaded on signed and unsigned integer - types, the new wording just maintains consistency. - - 22.4.2.1.2 [facet.num.get.virtuals] table 78... - </p> - <blockquote><p> - Table 78: Integer Conversions - </p> - <table border="1"> - <thead> - <tr> - <th>State</th> - <th><tt>stdio</tt> equivalent</th> - </tr> - </thead> - <tbody> - <tr> - <td><tt>basefield == oct</tt></td> - <td><tt>%o</tt></td> - </tr> - <tr> - <td><tt>basefield == hex</tt></td> - <td><tt>%X</tt></td> - </tr> - <tr> - <td><tt>basefield == 0</tt></td> - <td><tt>%i</tt></td> - </tr> - <tr> - <td><del>signed integral type</del><ins>signed integer - type</ins></td> - <td><tt>%d</tt></td> - </tr> - <tr> - <td><del>unsigned integral type</del><ins>unsigned integer - type</ins></td> - <td><tt>%u</tt></td> - </tr> - </tbody> - </table> - </blockquote> - - - - <p> - Rationale is same as above. - 22.4.2.2.2 [facet.num.put.virtuals] table 80... - </p> - <blockquote><p> - Table 80: Integer Conversions - </p> - <table border="1"> - <thead> - <tr> - <th>State</th> - <th><tt>stdio</tt> equivalent</th> - </tr> - </thead> - <tbody> - <tr> - <td><tt>basefield == ios_base::oct</tt></td> - <td><tt>%o</tt></td> - </tr> - <tr> - <td><tt>(basefield == ios_base::hex) && - !uppercase</tt></td> - <td><tt>%x</tt></td> - </tr> - <tr> - <td><tt>(basefield == ios_base::hex)</tt></td> - <td><tt>%X</tt></td> - </tr> - <tr> - <td><tt>basefield == 0</tt></td> - <td><tt>%i</tt></td> - </tr> - <tr> - <td>for a <del>signed integral type</del><ins>signed integer - type</ins></td> - <td><tt>%d</tt></td> - </tr> - <tr> - <td>for a <del>unsigned integral type</del><ins>unsigned integer - type</ins></td> - <td><tt>%u</tt></td> - </tr> - </tbody> - </table> - </blockquote> - - - <p> - 23.2 [container.requirements] table 80... - </p> - <blockquote><p> - Table 89: Container requirements - </p> - <table border="1"> - <thead> - <tr> - <th>expression</th> - <th>return type</th> - <th>operational semantics</th> - <th>assertion/note/pre/post-condition</th> - <th>complexity</th> - </tr> - </thead> - <tbody> - <tr> - <td><tt>X::difference_type</tt></td> - <td><del>signed integral type</del><ins>signed integer type</ins></td> - <td> </td> - <td>is identical to the difference type of <tt>X::iterator</tt> - and <tt>X::const_iterator</tt></td> - <td>compile time</td> - </tr> - <tr> - <td><tt>X::size_type</tt></td> - <td><del>unsigned integral type</del><ins>unsigned integer type</ins></td> - <td> </td> - <td><tt>size_type</tt> can represent any non-negative value of - <tt>difference_type</tt></td> - <td>compile time</td> - </tr> - </tbody> - </table> - </blockquote> - - <p> - X [iterator.concepts] paragraph 1... - </p> - <blockquote><p> - Iterators are a generalization of pointers that allow a C++ program to - work with different data structures (containers) in a uniform manner. - To be able to construct template algorithms that work correctly and - efficiently on different types of data structures, the library - formalizes not just the interfaces but also the semantics and - complexity assumptions of iterators. All input iterators - <code>i</code> support the expression <code>*i</code>, resulting in a - value of some class, enumeration, or built-in type <code>T</code>, - called the <i>value type</i> of the iterator. All output iterators - support the expression <code>*i = o</code> where <code>o</code> is a - value of some type that is in the set of types that are - <i>writable</i> to the particular iterator type of <code>i</code>. All - iterators <code>i</code> for which the expression <code>(*i).m</code> - is well-defined, support the expression <code>i->m</code> with the - same semantics as <code>(*i).m</code>. For every iterator type - <code>X</code> for which equality is defined, there is a corresponding - <del>signed integral type</del> <ins>signed integer type</ins> called - the <i>difference type</i> of the iterator. - </p></blockquote> - - <p> - I'm a little unsure of this change. Previously this paragraph would - allow instantiations of <tt>linear_congruential_engine</tt> on - <tt>char</tt>, <tt>wchar_t</tt>, <tt>bool</tt>, and other types. The - new wording prohibits this. - 26.5.3.1 [rand.eng.lcong] paragraph 2... - </p> - <blockquote><p> - The template parameter <code>UIntType</code> shall denote an - <del>unsigned integral type</del><ins>unsigned integer type</ins> - large enough to store values as large as <code>m - 1</code>. If the - template parameter <code>m</code> is 0, the modulus <code>m</code> - used throughout this section 26.4.3.1 is - <code>numeric_limits<result_type>::max()</code> plus 1. [Note: - The result need not be representable as a value of type - <code>result_type</code>. --end note] Otherwise, the following - relations shall hold: <code>a < m</code> and <code>c < - m</code>. - </p></blockquote> - - <p> - Same rationale as the previous change. - X [rand.adapt.xor] paragraph 6... - </p> - <blockquote><p> - Both <code>Engine1::result_type</code> and - <code>Engine2::result_type</code> shall denote (possibly different) - <del>unsigned integral types</del><ins>unsigned integer types</ins>. - The member <i>result_type</i> shall denote either the type - <i>Engine1::result_type</i> or the type <i>Engine2::result_type</i>, - whichever provides the most storage according to clause 3.9.1. - </p></blockquote> - - <p> - 26.5.7.1 [rand.util.seedseq] paragraph 7... - </p> - <blockquote><p> - <i>Requires:</i><code>RandomAccessIterator</code> shall meet the - requirements of a random access iterator (24.1.5) such that - <code>iterator_traits<RandomAccessIterator>::value_type</code> - shall denote an <del>unsigned integral type</del><ins>unsigned integer - type</ins> capable of accomodating 32-bit quantities. - </p></blockquote> - - <p> - By making this change, integral types that happen to have a signed - representation, but are not signed integer types, would no longer be - required to use a two's complement representation. This may go against - the original intent, and should be reviewed. - 29.6 [atomics.types.operations] paragraph 24... - </p> - <blockquote><p> - <i>Remark:</i> For <del>signed integral types</del><ins>signed integer - types</ins>, arithmetic is defined using two's complement - representation. There are no undefined results. For address types, the - result may be an undefined address, but the operations otherwise have - no undefined behavior. - </p></blockquote> - - - - - - -<hr> -<h3><a name="879"></a>879. Atomic load const qualification</h3> -<p><b>Section:</b> 29 [atomics] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alexander Chemeris <b>Opened:</b> 2008-08-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics">issues</a> in [atomics].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The <tt>atomic_address</tt> type and <tt>atomic<T*></tt> specialization provide atomic -updates to pointers. However, the current specification requires -that the types pointer be to non-const objects. This restriction -is unnecessary and unintended. -</p> - -<p><i>[ -Summit: -]</i></p> - -<blockquote><p> -Move to review. Lawrence will first check with Peter whether the -current examples are sufficient, or whether they need to be expanded to -include all cases. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote> -<p> -Lawrence will handle all issues relating to atomics in a single paper. -</p> -<p> -LWG will defer discussion on atomics until that paper appears. -</p> -<p> -Move to Open. -</p> -</blockquote> - -<p><i>[ -2009-08-17 Handled by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2925.html">N2925</a>. -]</i></p> - - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -NAD Editorial. Solved by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2992.htm">N2992</a>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add const qualification to the pointer values of the <tt>atomic_address</tt> -and <tt>atomic<T*></tt> specializations. E.g. -</p> - -<blockquote><pre> -typedef struct atomic_address { - void store(<ins>const</ins> void*, memory_order = memory_order_seq_cst) volatile; - void* exchange( <ins>const</ins> void*, memory_order = memory_order_seq_cst) volatile; - bool compare_exchange( <ins>const</ins> void*&, <ins>const</ins> void*, - memory_order, memory_order) volatile; - bool compare_exchange( <ins>const</ins> void*&, <ins>const</ins> void*, - memory_order = memory_order_seq_cst ) volatile; - void* operator=(<ins>const</ins> void*) volatile; -} atomic_address; - -void atomic_store(volatile atomic_address*, <ins>const</ins> void*); -void atomic_store_explicit(volatile atomic_address*, <ins>const</ins> void*, - memory_order); -void* atomic_exchange(volatile atomic_address*<ins>, const void*</ins>); -void* atomic_exchange_explicit(volatile atomic_address*, <ins>const</ins> void*, - memory_order); -bool atomic_compare_exchange(volatile atomic_address*, - <ins>const</ins> void**, <ins>const</ins> void*); -bool atomic_compare_exchange_explicit(volatile atomic_address*, - <ins>const</ins> void**, <ins>const</ins> void*, - memory_order, memory_order); -</pre></blockquote> - - - - - -<hr> -<h3><a name="887"></a>887. issue with condition::wait_...</h3> -<p><b>Section:</b> 30.5.1 [thread.condition.condvar] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Lawrence Crowl <b>Opened:</b> 2008-09-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.condition.condvar">issues</a> in [thread.condition.condvar].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The Posix/C++ working group has identified an inconsistency between -Posix and the C++ working draft in that Posix requires the clock to be -identified at creation, whereas C++ permits identifying the clock at the -call to wait. The latter cannot be implemented with the former. -</p> - -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote> -<p> -Howard recommends NAD with the following explanation: -</p> - -<p> -The intent of the current wording is for the <tt>condtion_variable::wait_until</tt> -be able to handle user-defined clocks as well as clocks the system knows about. -This can be done by providing overloads for the known clocks, and another -overload for unknown clocks which synchs to a known clock before waiting. -For example: -</p> - -<blockquote><pre> -template <class Duration> -bool -condition_variable::wait_until(unique_lock<mutex>& lock, - const chrono::time_point<chrono::system_clock, Duration>& abs_time) -{ - using namespace chrono; - nanoseconds d = __round_up<nanoseconds>(abs_time.time_since_epoch()); - __do_timed_wait(lock.mutex()->native_handle(), time_point<system_clock, nanoseconds>(d)); - return system_clock::now() < abs_time; -} - -template <class Clock, class Duration> -bool -condition_variable::wait_until(unique_lock<mutex>& lock, - const chrono::time_point<Clock, Duration>& abs_time) -{ - using namespace chrono; - system_clock::time_point s_entry = system_clock::now(); - typename Clock::time_point c_entry = Clock::now(); - nanoseconds dn = __round_up<nanoseconds>(abs_time.time_since_epoch() - - c_entry.time_since_epoch()); - __do_timed_wait(lock.mutex()->native_handle(), s_entry + dn); - return Clock::now() < abs_time; -} -</pre></blockquote> - -<p> -In the above example, <tt>system_clock</tt> is the only clock which the underlying -condition variable knows how to deal with. One overload just passes that clock -through. The second overload (approximately) converts the unknown clock into -a <tt>system_clock time_point</tt> prior to passing it down to the native -condition variable. -</p> - -<p> -On Posix systems vendors are free to add implementation defined constructors which -take a clock. That clock can be stored in the condition_variable, and converted -to (or not as necessary) as shown above. -</p> - -<p> -If an implementation defined constructor takes a clock (for example), then part -of the semantics for that implementation defined ctor might include that a -<tt>wait_until</tt> using a clock other than the one constructed with results -in an error (exceptional condition) instead of a conversion to the stored clock. -Such a design is up to the vendor as once an implementation defined ctor is used, -the vendor is free to specifiy the behavior of waits and/or notifies however -he pleases (when the cv is constructed in an implementation defined manner). -</p> -</blockquote> - -<p><i>[ -Post Summit: -]</i></p> - - -<blockquote> -<p> -"POSIX people will review the proposed NAD resolution at their upcoming NY -meeting. -</p> - -<p> -See the minutes at: <a href="http://wiki.dinkumware.com/twiki/bin/view/Posix/POSIX-CppBindingWorkingGroupNewYork2009">http://wiki.dinkumware.com/twiki/bin/view/Posix/POSIX-CppBindingWorkingGroupNewYork2009</a>. -</p> -</blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Move to NAD. -</p></blockquote> - -<p><i>[ -2009-07-18 Detlef reopens the issue: -]</i></p> - - -<blockquote> -<p> -On Friday afternoon in Frankfurt is was decided that 887 is NAD. -This decision was mainly based on a sample implementation presented -by Howard that implemented one clock on top of another. -Unfortunately this implementation doesn't work for the probably most -important case where a system has a monotonic clock and a real-time -clock (or "wall time" clock): -</p> -<p> -If the underlying "system_clock" is a monotonic clock, and -the program waits on the real-time clock, and the real-time clock -is set forward, the wait will unblock too late. -</p> - -<p> -If the underlying "system_clock" is a real-time clock, and the -program waits on the monotonic clock, and the real-time clock -is set back, the wait again will unblock too late. -</p> - -<p> -Sorry that I didn't remember this on Friday, but it was Friday -afternoon after a busy week... -</p> - -<p> -So as the decision was made on a wrong asumption, I propose to re-open -the issue. -</p> -</blockquote> - -<p><i>[ -2009-07-26 Howard adds: -]</i></p> - - -<blockquote> -<p> -Detlef correctly argues that <tt>condition_variable::wait_until</tt> could -return "too late" in the context of clocks being adjusted during the wait. I agree -with his logic. But I disagree that this makes this interface unimplementable -on POSIX. -</p> - -<p> -The POSIX spec also does not guarantee that <tt>pthread_cond_timedwait</tt> does -not return "too late" when clocks are readjusted during the wait. Indeed, the -POSIX specification lacks any requirements at all concerning how soon -<tt>pthread_cond_timedwait</tt> returns after a time out. This is evidently a -QOI issue by the POSIX standard. Here is a quote of the most relevant normative -text concerning <tt>pthread_cond_timedwait</tt> found -<a href="http://www.unix.org/single_unix_specification/">here</a>. -</p> - -<blockquote><p> -The <tt>pthread_cond_timedwait()</tt> function shall be equivalent to -<tt>pthread_cond_wait()</tt>, except that an error is returned if the absolute -time specified by <tt>abstime</tt> passes (that is, system time equals or exceeds -<tt>abstime</tt>) before the condition <tt>cond</tt> is signaled or broadcasted, or if the -absolute time specified by <tt>abstime</tt> has already been passed at the time -of the call. -</p></blockquote> - -<p> -I.e. the POSIX specification speaks of the error code returned in case of a time -out, but not on the timeliness of that return. -</p> - -<p> -Might this simply be an oversight, or minor defect in the POSIX specification? -</p> - -<p> -I do not believe so. This same section goes on to say in <em>non-normative</em> -text: -</p> - -<blockquote><p> -For cases when the system clock is advanced discontinuously by an -operator, it is expected that implementations process any timed wait -expiring at an intervening time as if that time had actually occurred. -</p></blockquote> - -<p> -Here is non-normative wording encouraging the implementation to ignore an advancing -underlying clock and subsequently causing an early (spurious) return. There is -no wording at all which addresses Detlef's example of a "late return". With -<tt>pthread_cond_timedwait</tt> this would be caused by setting the system clock -backwards. It seems reasonable to assume, based on the wording that is already -in the POSIX spec, that again, the discontinuously changed clock would be ignored -by <tt>pthread_cond_timedwait</tt>. -</p> - -<p> -A noteworthy difference between <tt>pthread_cond_timedwait</tt> and -<tt>condition_variable::wait_until</tt> is that the POSIX spec appears to -say that <tt>ETIMEDOUT</tt> should be returned if <tt>pthread_cond_timedwait</tt> -returns because of timeout signal, whether or not the system clock was discontinuously -advanced during the wait. In contrast <tt>condition_variable::wait_until</tt> -always returns: -</p> - -<blockquote><pre> -<tt>Clock::now() < abs_time</tt> -</pre></blockquote> - -<p> -That is, the C++ spec requires that the clock be rechecked (detecting discontinuous -adjustments during the wait) at the time of return. <tt>condition_variable::wait_until</tt> -may indeed return early or late. But regardless it will return a value -reflecting timeout status at the time of return (even if clocks have been adjusted). -Of course the clock may be adjusted after the return value is computed but before the client has -a chance to read the result of the return. Thus there are no iron-clad guarantees -here. -</p> - -<p> -<tt>condition_variable::wait_until</tt> (and <tt>pthread_cond_timedwait</tt>) -is little more than a convenience function for making sure -<tt>condition_variable::wait</tt> doesn't hang for an unreasonable amount of -time (where the client gets to define "unreasonable"). I do not think it -is in anyone's interest to try to make it into anything more than that. -</p> - -<p> -I maintain that this is a useful and flexible specification in the spirit of -C++, and is implementable on POSIX. The implementation technique described above -is a reasonable approach. There may also be higher quality approaches. This -specification, like the POSIX specification, gives a wide latitude for QOI. -</p> - -<p> -I continue to recommend NAD, but would not object to a clarifying note regarding -the behavior of <tt>condition_variable::wait_until</tt>. At the moment, I do -not have good wording for such a note, but welcome suggestions. -</p> - -</blockquote> - -<p><i>[ -2009-09-30: See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2969.html">N2969</a>. -]</i></p> - - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -The LWG is in favor of Detlef to supply revision which adopts Option 2 from -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2969.html">N2969</a> -but is modified by saying that <tt>system_clock</tt> must be available for <tt>wait_until</tt>. -</p></blockquote> - -<p><i>[ -2010-02-11 Anthony provided wording. -]</i></p> - - -<p><i>[ -2010-02-22 Anthony adds: -]</i></p> - - -<blockquote> -<p> -I am strongly against -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2999.html">N2999</a>. -</p> - -<p> -Firstly, I think that the most appropriate use of a timed wait on a condition -variable is with a monotonic clock, so it ought to be guaranteed to be available -on systems that support such a clock. Also, making the set of supported clocks -implementation defined essentially kills portability around the use of -user-defined clocks. -</p> - -<p> -I also think that <tt>wait_for</tt> is potentially useful, and trivially -implementable given a working templated <tt>wait_until</tt> and a monotonic -clock. -</p> - -<p> -I also disagree with many of Detlef's points in the rationale. In a system with -hard latency limits there is likely to be a monotonic clock, otherwise you have -no way of measuring against these latency limits since the <tt>system_clock</tt> -may change arbitrarily. In such systems, you <em>want</em> to be able to use -<tt>wait_for</tt>, or <tt>wait_until</tt> with a monotonic clock. -</p> - -<p> -I disagree that the <tt>wait_*</tt> functions cannot be implemented correctly on -top of POSIX: I have done so. The only guarantee in the working draft is that -when the function returns certain properties are true; there is no guarantee -that the function will return <em>immediately</em> that the properties are true. -My resolution to issue 887 makes this clear. How small the latency is is QoI. -</p> - -<p> -On systems without a monotonic clock, you cannot measure the problem since the -system clock can change arbitrarily so any timing calculations you make may be -wrong due to clock changes. -</p> - -<p> -On systems with a monotonic clock, you can choose to use it for your condition -variables. If you are waiting against a <tt>system_clock::time_point</tt> then -you can check the clock when waking, and either return as a timeout or spurious -wake depending on whether <tt>system_clock::now()</tt> is before or after the -specified <tt>time_point</tt>. -</p> - -<p> -Windows <em>does</em> provide condition variables from Vista onwards. I choose -not to use them, but they are there. If people are concerned about -implementation difficulty, the Boost implementation can be used for most -purposes; the Boost license is pretty liberal in that regard. -</p> - -<p> -My preferred resolution to issue 887 is currently the PR in the issues list. -</p> -</blockquote> - -<p><i>[ -2010 Pittsburgh: -]</i></p> - - -<blockquote> -<p> -There is no consensus for moving the related paper -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2999.html">N2999</a> -into the WP. -</p> -<p> -There was support for moving this issue as proposed to Ready, but the support -was insufficient to call a consensus. -</p> -<p> -There was consensus for moving this issue to NAD as opposed to leaving it open. -Rationale added. -</p> -</blockquote> - - - -<p><b>Rationale:</b></p> -<p> -The standard as written is sufficiently implementable and self consistent. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add a new paragraph after 30.2.4 [thread.req.timing]p3: -</p> - -<blockquote> -<p> -3 The resolution of timing provided by an implementation depends on both -operating system and hardware. The finest resolution provided by an -implementation is called the <i>native resolution</i>. -</p> - -<p><ins> -If a function in this clause takes a timeout argument, and the time point or -elapsed time specified passes before the function returns, the latency between -the timeout occurring and the function returning is unspecified [<i>Note:</i> -Implementations should strive to keep such latency as small as possible, but -portable code should not rely on any specific upper limits — <i>end -note</i>] -</ins></p> -</blockquote> - - - - - -<hr> -<h3><a name="892"></a>892. Forward_list issues...</h3> -<p><b>Section:</b> 23.3.4.6 [forwardlist.ops] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Ed Smith-Rowland <b>Opened:</b> 2008-09-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#forwardlist.ops">issues</a> in [forwardlist.ops].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I was looking at the latest draft on <tt>forward_list</tt>. Especially the splice methods. -</p> -<p> -The first one splices a whole list after a given iterator in <tt>this</tt>. The name is <tt>splice_after</tt>. -I think in 23.3.4.6 [forwardlist.ops] paragraph 40 -change: -</p> -<blockquote><p> -<i>Effect:</i> Insert the contents of <tt>x</tt> <del>before</del> <ins>after</ins> <tt>position</tt>, ... -</p></blockquote> - -<p> -A deeper issue involves the complexity. <tt>forward_list</tt> has no <tt>size</tt> and we -don't know when we've reached the end except to walk up to it. To -splice we would need to hook the end of the source list to the item -after <tt>position</tt> in this list. This would involve walking length of the -source list until we got to the last dereference-able element in source. -There's no way we could do this in O(1) unless we stored a bogus end in -<tt>forward_list</tt>. -</p> -<p> -OTOH, the last version of <tt>splice_after</tt> with iterator ranges we could do -in O(1) because we know how to hook the end of the source range to ... -</p> -<p> -Unless I'm misconceiving the whole thing. Which is possible. I'll look at it again. -</p> -<p> -I'm pretty sure about the first part though. -</p> - -<p><i>[ -San Francisco: -]</i></p> - - -<blockquote> -<p> -This issue is more complicated than it looks. -</p> -<p> -paragraph 47: replace each <tt>(first, last) with (first, last]</tt> -</p> -<p> -add a statement after paragraph 48 that complexity is O(1) -</p> -<p> -remove the complexity statement from the first overload of splice_after -</p> -<p> -We may have the same problems with other modifiers, like erase_after. -Should it require that all iterators in the range (position, last] be -dereferenceable? -</p> -<p> -We do, however, like the proposed changes and consider them Editorial. -Move to NAD Editorial, Pending. Howard to open a new issue to handle the -problems with the complexity requirements. -</p> -<p> -Opened <a href="lwg-defects.html#897">897</a>. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -In 23.3.4.6 [forwardlist.ops] paragraph 40 -change: -</p> -<blockquote><p> -<i>Effect:</i> Insert the contents of <tt>x</tt> <del>before</del> <ins>after</ins> <tt>position</tt>, ... -</p></blockquote> - - - - - -<hr> -<h3><a name="895"></a>895. "Requires:" on std::string::at et al</h3> -<p><b>Section:</b> 17.5.1.4 [structure.specifications] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> James Dennett <b>Opened:</b> 2008-09-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#structure.specifications">issues</a> in [structure.specifications].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#625">625</a></p> -<p><b>Discussion:</b></p> -<p> -Per discussion, we need an issue open to cover looking at "Requires" -clauses which are not constraints on user code, such as that on -<tt>std::basic_string::at</tt>. -</p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> - Alan to address in paper. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="901"></a>901. insert iterators can move from lvalues</h3> -<p><b>Section:</b> 24.5.2.5 [insert.iterator] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2008-09-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses UK 282</b></p> - -<p> -The requires clause on the <tt>const T &</tt> overloads in -<tt>back_insert_iterator/front_insert_iterator/insert_iterator</tt> mean that the -assignment operator will implicitly move from lvalues of a move-only type. -</p> -<p> -Suggested resolutions are: -</p> -<ol style="list-style-type:lower-alpha"> -<li> -Add another overload with a negative constraint on copy-constructible -and flag it "= delete". -</li> -<li> -Drop the copy-constructible overload entirely and rely on perfect -forwarding to catch move issues one level deeper. -</li> -<li> -This is a fundamental problem in move-syntax that relies on the -presence of two overloads, and we need to look more deeply into this -area as a whole - do not solve this issue in isolation. -</li> -</ol> - -<p><i>[ -Post Summit, Alisdair adds: -]</i></p> - - -<blockquote> -<p> -Both comment and issue have been resolved by the adoption of -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2844.html">N2844</a> -(rvalue references safety fix) at the last meeting. -</p> - -<p> -Suggest resolve as NAD Editorial with a reference to the paper. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree that this has been resolved in the latest Working Draft. -Move to NAD. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Recommend NAD, addressed by <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2844.html">N2844</a>. -</p> - - - - - -<hr> -<h3><a name="902"></a>902. Regular is the wrong concept to constrain numeric_limits</h3> -<p><b>Section:</b> 18.3.2 [limits] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2008-09-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#limits">issues</a> in [limits].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses FR 32 and DE 16</b></p> - -<p> -<tt>numeric_limits</tt> has functions specifically designed to return NaNs, which -break the model of <tt>Regular</tt> (via its axioms.) While floating point types -will be acceptible in many algorithms taking <tt>Regular</tt> values, it is not -appopriate for this specific API and we need a less refined constraint. -</p> - -<p>FR 32:</p> - -<blockquote><p> -The definition of <tt>numeric_limits<></tt> as requiring a regular -type is both conceptually wrong and operationally illogical. As we -pointed before, this mistake needs to be corrected. For example, the -template can be left unconstrained. In fact this reflects a much more -general problem with concept_maps/axioms and their interpretations. It -appears that the current text heavily leans toward experimental academic -type theory. -</p></blockquote> - -<p>DE 16:</p> - -<blockquote><p> -The class template <tt>numeric_limits</tt> should not specify the Regular concept -requirement for its template parameter, because it contains functions -returning NaN values for floating-point types; these values violate the -semantics of EqualityComparable. -</p></blockquote> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Move to Open. Alisdair and Gaby will work on a solution, along with the new -treatment of axioms in clause 14. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="903"></a>903. <tt>back_insert_iterator</tt> issue</h3> -<p><b>Section:</b> 24.5.2.1 [back.insert.iterator] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Dave Abrahams <b>Opened:</b> 2008-09-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I just noticed this; don't know how far the problem(?) extends or -whether it's new or existing: <tt>back_insert_iterator</tt>'s <tt>operator*</tt> is not -<tt>const</tt>, so you can't dereference a <tt>const</tt> one. -</p> - -<p><i>[ -Post Summit Daniel adds: -]</i></p> - - -<blockquote> -<p> -If done, this change should be applied for <tt>front_insert_iterator</tt>, -<tt>insert_iterator</tt>, <tt>ostream_iterator</tt>, and <tt>ostreambuf_iterator</tt> as well. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Alisdair notes that these all are output iterators. -Howard points out that <tt>++*i</tt> -would no longer work if we made this change. -</p> -<p> -Move to NAD. -</p> -</blockquote> - -<p><i>[ -2009-05-25 Daniel adds: -]</i></p> - - -<ol> -<li> -If <a href="lwg-closed.html#1009">1009</a> is accepted, <tt>OutputIterator</tt> does no longer support post increment. -</li> -<li> -To support backward compatibility a second overload of <tt>operator*</tt> -can be added. -Note that the <tt>HasDereference</tt> concept (and the <tt>HasDereference</tt> part of concept -<tt>Iterator</tt>) was specifically refactored to cope with optional const -qualification and -to properly reflect the dual nature of built-in <tt>operator*</tt> as of -13.5.8 [over.literal]/6. -</li> -</ol> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="905"></a>905. Mutex specification questions</h3> -<p><b>Section:</b> 30.4.1.2.1 [thread.mutex.class] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Herb Sutter <b>Opened:</b> 2008-09-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.mutex.class">issues</a> in [thread.mutex.class].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#893">893</a></p> -<p><b>Discussion:</b></p> -<p> -A few questions on the current WP, -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2723.pdf">N2723</a>: -</p> -<p> -30.4.1 [thread.mutex.requirements]/24 says an expression -<tt>mut.unlock()</tt> "Throws: Nothing." I'm assuming that, per 17.6.4.11 [res.on.required], errors that violate the precondition "The -calling thread shall own the mutex" opens the door for throwing an -exception anyway, such as to report unbalanced unlock operations and -unlocking from a thread that does not have ownership. Right? -</p> -<p> -30.4.1.2.1 [thread.mutex.class]/3 (actually numbered paragraph "27" -in the WP; this is just a typo I think) says -</p> -<blockquote> -<p> -The behavior of a program is undefined if: -</p> -<ul> -<li>it destroys a <tt>mutex</tt> object owned by any thread,</li> -<li>a thread that owns a <tt>mutex</tt> object calls <tt>lock()</tt> or <tt>try_lock()</tt> on that object, or</li> -<li>a thread terminates while owning a <tt>mutex</tt> object.</li> -</ul> -</blockquote> - -<p> -As already discussed, I think the second bullet should be removed, and -such a <tt>lock()</tt> or <tt>try_lock()</tt> should fail with an -exception or returning <tt>false</tt>, respectively. -</p> -<p> -A potential addition to the list would be -</p> -<ul> -<li>a thread unlocks a <tt>mutex</tt> it does not have ownership of.</li> -</ul> -<p> -but without that the status quo text endorses the technique of the -program logically transferring ownership of a mutex to another thread -with correctness enforced by programming discipline. Was that intended? -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote> -<p> -Two resolutions: "not a defect" and "duplicate", as follows: -</p> -<ul> -<li> -30.4.1 [thread.mutex.requirements]/24: NAD. If the precondition -fails the program has undefined behaviour and therefore an -implementation may throw an exception already. -</li> -<li> -30.4.1.2.1 [thread.mutex.class]/3 bullet 2: Already addressed by issue <a href="lwg-defects.html#893">893</a>. -</li> -<li> -30.4.1.2.1 [thread.mutex.class]/3 proposed addition: NAD. This is -already covered by the mutex requirements, which have ownership as a -Precondition. -</li> -</ul> -</blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - - -<hr> -<h3><a name="906"></a>906. <tt>ObjectType</tt> is the wrong concept to constrain <tt>initializer_list</tt></h3> -<p><b>Section:</b> 18.9 [support.initlist] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2008-09-26 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#support.initlist">active issues</a> in [support.initlist].</p> -<p><b>View all other</b> <a href="lwg-index.html#support.initlist">issues</a> in [support.initlist].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The currently proposed constraint on <tt>initializer_list</tt>'s element type -<tt>E</tt> is that is has to meet <tt>ObjectType</tt>. This is an underspecification, -because both core language and library part of <tt>initializer_list</tt> -make clear, that it references an implicitly allocated array: -</p> -<p> -8.5.4 [dcl.init.list]/4: -</p> -<blockquote><p> -When an initializer list is implicitly converted to a -<tt>std::initializer_list<E></tt>, the object passed is constructed as if the -implementation allocated an array of N elements of type <tt>E</tt>, where -N is the number of elements in the initializer list.[..] -</p></blockquote> - -<p> -18.9 [support.initlist]/2. -</p> - -<blockquote><p> -An object of type <tt>initializer_list<E></tt> provides access to an array of -objects of type <tt>const E</tt>.[..] -</p></blockquote> - -<p> -Therefore, <tt>E</tt> needs to fulfill concept <tt>ValueType</tt> (thus excluding -abstract class types). This stricter requirement should be added -to prevent deep instantiation errors known from the bad old times, -as shown in the following example: -</p> - -<blockquote><pre> -// Header A: (Should concept-check even in stand-alone modus) - -template <DefaultConstructible T> -requires MoveConstructible<T> -void generate_and_do_3(T a) { - std::initializer_list<T> list{T(), std::move(a), T()}; - ... -} - -void do_more(); -void do_more_or_less(); - -template <DefaultConstructible T> -requires MoveConstructible<T> -void more_generate_3() { - do_more(); - generate_and_do_3(T()); -} - -template <DefaultConstructible T> -requires MoveConstructible<T> -void something_and_generate_3() { - do_more_or_less(); - more_generate_3(); -} - -// Test.cpp - -#include "A.h" - -class Abstract { -public: - virtual ~Abstract(); - virtual void foo() = 0; // abstract type - Abstract(Abstract&&){} // MoveConstructible - Abstract(){} // DefaultConstructible -}; - -int main() { - // The restricted template *accepts* the argument, but - // causes a deep instantiation error in the internal function - // generate_and_do_3: - something_and_generate_3<Abstract>(); -} -</pre></blockquote> - -<p> -The proposed stricter constraint does not minimize the aim to -support more general containers for which <tt>ObjectType</tt> would be -sufficient. If such an extended container (lets assume it's still a -class template) provides a constructor that accepts an <tt>initializer_list</tt> -only <em>this</em> constructor would need to be restricted on <tt>ValueType</tt>: -</p> - -<blockquote><pre> -template<ObjectType T> -class ExtContainer { -public: - requires ValueType<T> - ExtContainer(std::initializer_list<T>); - ... -}; -</pre></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to Tentatively Ready. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Need to look at again without concepts. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -In 18.9 [support.initlist]/p.1 replace in "header <tt><initializer_list></tt> synopsis" -the constraint "<tt>ObjectType</tt>" in the template parameter list by the -constraint "<tt>ValueType</tt>". -</li> -</ol> - - - - - - -<hr> -<h3><a name="910"></a>910. Effects of MoveAssignable</h3> -<p><b>Section:</b> 17.6.3.1 [utility.arg.requirements] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alberto Ganesh Barbati <b>Opened:</b> 2008-09-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#utility.arg.requirements">issues</a> in [utility.arg.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses UK 150</b></p> - -<p> -The description of the effect of <tt>operator=</tt> in the <tt>MoveAssignable</tt> -concept, given in paragraph 7 is: -</p> - -<blockquote><pre> -result_type T::operator=(T&& rv); // inherited from HasAssign<T, T&&> -</pre> - -<blockquote><p> -<i>Postconditions:</i> the constructed <tt>T</tt> object is equivalent to the value of -<tt>rv</tt> before the assignment. [<i>Note:</i> there is no -requirement on the value of <tt>rv</tt> after the assignment. <i>--end note</i>] -</p></blockquote> -</blockquote> - -<p> -The sentence contains a typo (what is the "constructed <tt>T</tt> object"?) -probably due to a cut&paste from <tt>MoveConstructible</tt>. Moreover, the -discussion of LWG issue <a href="lwg-defects.html#675">675</a> shows that the postcondition is too generic -and might not reflect the user expectations. An implementation of the -move assignment that just calls <tt>swap()</tt> would always fulfill the -postcondition as stated, but might have surprising side-effects in case -the source rvalue refers to an object that is not going to be -immediately destroyed. See LWG issue <a href="lwg-defects.html#900">900</a> for another example. Due to -the sometimes intangible nature of the "user expectation", it seems -difficult to have precise normative wording that could cover all cases -without introducing unnecessary restrictions. However a non-normative -clarification could be a very helpful warning sign that swapping is not -always the correct thing to do. -</p> - -<p><i>[ -2009-05-09 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -Issue 910 is exactly the reason BSI advanced the Editorial comment UK-150. -</p> -<p> -The post-conditions after assignment are at a minimum that the object -referenced by rv must be safely destructible, and the transaction should not -leak resources. Ideally it should be possible to simply assign rv a new -valid state after the call without invoking undefined behaviour, but any -other use of the referenced object would depend upon additional guarantees -made by that type. -</p> -</blockquote> - -<p><i>[ -2009-05-09 Howard adds: -]</i></p> - - -<blockquote> -<p> -The intent of the rvalue reference work is that the moved from <tt>rv</tt> is -a valid object. Not one in a singular state. If, for example, the moved from -object is a <tt>vector</tt>, one should be able to do anything on that moved-from -<tt>vector</tt> that you can do with any other <tt>vector</tt>. However you would -first have to query it to find out what its current state is. E.g. it might have <tt>capacity</tt>, -it might not. It might have a non-zero <tt>size</tt>, it might not. But regardless, -you can <tt>push_back</tt> on to it if you want. -</p> - -<p> -That being said, most standard code is now conceptized. That is, the concepts -list the only operations that can be done with templated types - whether or not -the values have been moved from. -</p> - -<p> -Here is user-written code which must be allowed to be legal: -</p> -<blockquote><pre> -#include <vector> -#include <cstdio> - -template <class Allocator> -void -inspect(std::vector<double, Allocator>&& v) -{ - std::vector<double, Allocator> result(move(v)); - std::printf("moved from vector has %u size and %u capacity\n", v.size(), v.capacity()); - std::printf("The contents of the vector are:\n"); - typedef typename std::vector<double, Allocator>::iterator I; - for (I i = v.begin(), e = v.end(); i != e; ++i) - printf("%f\n", *i); -} - -int main() -{ - std::vector<double> v1(100, 5.5); - inspect(move(v1)); -} -</pre></blockquote> - -<p> -The above program does not treat the moved-from <tt>vector</tt> as singular. It -only treats it as a <tt>vector</tt> with an unknown value. -</p> -<p> -I believe the current proposed wording is consistent with my view on this. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree that the proposed resolution -is an improvement over the current wording. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Need to look at again without concepts. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Walter will consult with Dave and Doug. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -We believe this is handled by the resolution to issue <a href="lwg-defects.html#1204">1204</a>, -but there is to much going on in this area to be sure. Defer for now. -</p></blockquote> - -<p><i>[ -2010-01-23 Moved to Tentatively NAD Concepts after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - -<p><b>Rationale:</b></p> -<p> -The current <tt>MoveAssignable</tt> requirements say everything that can be said -in general. Each std-defined type has a more detailed specification of move -assignment. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In [concept.copymove], replace the postcondition in paragraph 7 with: -</p> - -<blockquote><p> -<i>Postconditions:</i> <tt>*this</tt> is equivalent to the value of <tt>rv</tt> before the -assignment. [<i>Note:</i> there is no requirement on the value of <tt>rv</tt> after the -assignment, but the -effect should be unsurprising to the user even in case <tt>rv</tt> is not -immediately destroyed. This may require that resources previously owned -by <tt>*this</tt> are released instead of transferred to <tt>rv</tt>. <i>-- end note</i>] -</p></blockquote> - - - - - -<hr> -<h3><a name="912"></a>912. Array swap needs to be conceptualized</h3> -<p><b>Section:</b> 25.3.3 [alg.swap] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2008-10-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.swap">issues</a> in [alg.swap].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -With the adaption of <a href="lwg-defects.html#809">809</a> -we have a new algorithm <tt>swap</tt> for C-arrays, which needs to be conceptualized. -</p> - -<p><i>[ -Post Summit Daniel adds: -]</i></p> - - -<blockquote><p> -Recommend as NAD Editorial: The changes have already been applied to the WP -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2800.pdf">N2800</a>. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to NAD; the changes have already been made. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Replace in 25.3.3 [alg.swap] before p. 3 until p. 4 by -</p> - -<blockquote><pre> -template <<del>class</del> <ins>ValueType</ins> T, size_t N> -<ins>requires Swappable<T></ins> -void swap(T (&a)[N], T (&b)[N]); -</pre> -<blockquote> -<p> -<del><i>Requires:</i> <tt>T</tt> shall be <tt>Swappable</tt>.</del> -</p> -<p> -<i>Effects:</i> <tt>swap_ranges(a, a + N, b);</tt> -</p> -</blockquote> -</blockquote> - - - - - - -<hr> -<h3><a name="913"></a>913. Superfluous requirements for replace algorithms</h3> -<p><b>Section:</b> 25.3.5 [alg.replace] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2008-10-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.replace">issues</a> in [alg.replace].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -(A) 25.3.5 [alg.replace]/1: -</p> - -<blockquote><p> -<i>Requires:</i> The expression <tt>*first = new_value</tt> shall be valid. -</p></blockquote> - -<p> -(B) 25.3.5 [alg.replace]/4: -</p> - -<blockquote><p> -<i>Requires:</i> The results of the expressions <tt>*first</tt> and <tt>new_value</tt> shall -be writable to the result output iterator.[..] -</p></blockquote> - -<p> -Since conceptualization, the quoted content of these clauses is covered -by the existing requirements -</p> - -<p> -(A) <tt>OutputIterator<Iter, const T&></tt> -</p> - -<p> -and -</p> - -<p> -(B) <tt>OutputIterator<OutIter, InIter::reference> && OutputIterator<OutIter, const T&></tt> -</p> - -<p> -resp, and thus should be removed. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree with the proposed resolution. -</p> -<p> -Move to Tentatively Ready. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<ol style="list-style-type:upper-alpha"> -<li> -<p> -Remove 25.3.5 [alg.replace]/1. -</p> -<blockquote><pre> -template<ForwardIterator Iter, class T> - requires OutputIterator<Iter, Iter::reference> - && OutputIterator<Iter, const T&> - && HasEqualTo<Iter::value_type, T> - void replace(Iter first, Iter last, - const T& old_value, const T& new_value); - -template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred, class T> - requires OutputIterator<Iter, Iter::reference> - && OutputIterator<Iter, const T&> - && CopyConstructible<Pred> - void replace_if(Iter first, Iter last, - Pred pred, const T& new_value); -</pre> -<blockquote><p> -<del>1 <i>Requires:</i> The expression <tt>*first = new_value</tt> shall be valid.</del> -</p></blockquote> -</blockquote> -</li> -<li> -<p> -25.3.5 [alg.replace]/4: Remove the sentence "The results of the -expressions <tt>*first</tt> and -<tt>new_value</tt> shall be writable to the result output iterator.". -</p> -<blockquote><pre> -template<InputIterator InIter, typename OutIter, class T> - requires OutputIterator<OutIter, InIter::reference> - && OutputIterator<OutIter, const T&> - && HasEqualTo<InIter::value_type, T> - OutIter replace_copy(InIter first, InIter last, - OutIter result, - const T& old_value, const T& new_value); - -template<InputIterator InIter, typename OutIter, - Predicate<auto, InIter::value_type> Pred, class T> - requires OutputIterator<OutIter, InIter::reference> - && OutputIterator<OutIter, const T&> - && CopyConstructible<Pred> - OutIter replace_copy_if(InIter first, InIter last, - OutIter result, - Pred pred, const T& new_value); -</pre> -<blockquote><p> -4 <i>Requires:</i> <del>The results of the expressions <tt>*first</tt> and -<tt>new_value</tt> shall be writable to the <tt>result</tt> output -iterator.</del> The ranges <tt>[first,last)</tt> and <tt>[result,result + -(last - first))</tt> shall not overlap. -</p></blockquote> -</blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="914"></a>914. Superfluous requirement for unique</h3> -<p><b>Section:</b> 25.3.9 [alg.unique] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2008-10-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.unique">issues</a> in [alg.unique].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -25.3.9 [alg.unique]/2: "Requires: The comparison function shall be an -equivalence relation." -</p> - -<p> -The essence of this is already covered by the given requirement -</p> - -<blockquote><pre> -EquivalenceRelation<auto, Iter::value_type> Pred -</pre></blockquote> - -<p> -and should thus be removed. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the proposed resolution. -Move to Tentatively Ready. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Remove 25.3.9 [alg.unique]/2 -</p> - -<blockquote><pre> -template<ForwardIterator Iter> - requires OutputIterator<Iter, Iter::reference> - && EqualityComparable<Iter::value_type> - Iter unique(Iter first, Iter last); - -template<ForwardIterator Iter, EquivalenceRelation<auto, Iter::value_type> Pred> - requires OutputIterator<Iter, RvalueOf<Iter::reference>::type> - && CopyConstructible<Pred> - Iter unique(Iter first, Iter last, - Pred pred); -</pre> -<blockquote> -<p> -1 <i>Effects:</i> ... -</p> -<p> -<del>2 <i>Requires:</i> The comparison function shall be an equivalence relation.</del> -</p> -</blockquote> -</blockquote> - - - - - -<hr> -<h3><a name="915"></a>915. <tt>minmax</tt> with <tt>initializer_list</tt> should return -<tt>pair</tt> of <tt>T</tt>, not <tt>pair</tt> of <tt>const T&</tt></h3> -<p><b>Section:</b> 25.4.7 [alg.min.max] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2008-10-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.min.max">issues</a> in [alg.min.max].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -It seems that the proposed changes for -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2772.pdf">N2772</a> -were not clear enough in -this point: -</p> - -<blockquote><p> -25.4.7 [alg.min.max], before p.23 + p.24 + before p. 27 + p. 28 say that the return -type of the <tt>minmax</tt> overloads with an <tt>initializer_list</tt> is -<tt>pair<const T&, const T&></tt>, -which is inconsistent with the decision for the other <tt>min/max</tt> overloads which take -a <tt>initializer_list</tt> as argument and return a <tt>T</tt>, not a <tt>const T&</tt>. -Doing otherwise for <tt>minmax</tt> would easily lead to unexpected life-time -problems by using <tt>minmax</tt> instead of <tt>min</tt> and <tt>max</tt> separately. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the proposed resolution. -Move to Tentatively Ready. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -Moved from Tentatively Ready to Open only because the wording needs to be -tweaked for concepts removal. -</p></blockquote> - -<p><i>[ -2009-08-18 Daniel adds: -]</i></p> - - -<blockquote><p> -Recommend NAD since the proposed changes have already been performed -as part of editorial work of -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2914.pdf">N2914</a>. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Can't find <tt>initializer_list</tt> form of <tt>minmax</tt> anymore, only variadic -version. Seems like we had an editing clash with concepts. Leave Open, -at least until editorial issues resolved. Bring this to Editor's attention. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: Pete to reapply -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2772.pdf">N2772</a>. -]</i></p> - - - - -<p><b>Rationale:</b></p><p> -Solved by reapplying -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2772.pdf">N2772</a>. -</p> - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -<p> -In 25 [algorithms]/2, header <tt><algorithm></tt> synopsis change as indicated: -</p> - -<blockquote><pre> -template<<del>class</del><ins>LessThanComparable</ins> T> -<ins>requires CopyConstructible<T></ins> -pair<<del>const </del>T<del>&</del>, <del>const </del>T<del>&</del>> -minmax(initializer_list<T> t); - -template<class T, <del>class</del><ins>StrictWeakOrder<auto, T></ins> Compare> -<ins>requires CopyConstructible<T></ins> -pair<<del>const </del>T<del>&</del>, <del>const </del>T<del>&</del>> -minmax(initializer_list<T> t, Compare comp); -</pre></blockquote> -</li> -<li> -<p> -In 25.4.7 [alg.min.max] change as indicated (Begin: Just before p.20): -</p> -<blockquote><pre> -template<<del>class</del><ins>LessThanComparable</ins> T> - <ins>requires CopyConstructible<T></ins> - pair<<del>const </del>T<del>&</del>, <del>const </del>T<del>&</del>> - minmax(initializer_list<T> t); -</pre> -<blockquote> -<p> -<del>-20- <i>Requires:</i> <tt>T</tt> is <tt>LessThanComparable</tt> and -<tt>CopyConstructible</tt>.</del> -</p> -<p> --21- <i>Returns:</i> <tt>pair<<del>const </del>T<del>&</del>, <del>const -</del>T<del>&</del>>(x, y)</tt> where <tt>x</tt> is the -smallest value and <tt>y</tt> the largest value in the <tt>initializer_list</tt>. -</p> -</blockquote> - -<p>[..]</p> -<pre> -template<class T, <del>class</del><ins>StrictWeakOrder<auto, T></ins> Compare> - <ins>requires CopyConstructible<T></ins> - pair<<del>const </del>T<del>&</del>, <del>const </del>T<del>&</del>> - minmax(initializer_list<T> t, Compare comp); -</pre> - -<blockquote> -<p> -<del>-24- <i>Requires:</i> type <tt>T</tt> is <tt>LessThanComparable</tt> and <tt>CopyConstructible</tt>.</del> -</p> -<p> --25- <i>Returns:</i> <tt>pair<<del>const </del>T<del>&</del>, <del>const -</del>T<del>&</del>>(x, y)</tt> where <tt>x</tt> is the -smallest value and <tt>y</tt> largest value in the <tt>initializer_list</tt>. -</p> -</blockquote> -</blockquote> -</li> -</ol> - - - - - - -<hr> -<h3><a name="916"></a>916. Redundant move-assignment operator of <tt>pair</tt> should be removed</h3> -<p><b>Section:</b> 20.3 [pairs] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2008-10-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#pairs">issues</a> in [pairs].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>see also <a href="lwg-closed.html#917">917</a>.</b></p> - -<p> -The current WP provides the following assignment operators for <tt>pair</tt> -in 20.3 [pairs]/1: -</p> - -<ol> -<li> -<pre> -template<class U , class V> -requires HasAssign<T1, const U&> && HasAssign<T2, const V&> -pair& operator=(const pair<U , V>& p); -</pre> -</li> -<li> -<pre> -requires MoveAssignable<T1> && MoveAssignable<T2> pair& operator=(pair&& p ); -</pre> -</li> -<li> -<pre> -template<class U , class V> -requires HasAssign<T1, RvalueOf<U>::type> && HasAssign<T2, RvalueOf<V>::type> -pair& operator=(pair<U , V>&& p); -</pre> -</li> -</ol> - -<p> -It seems that the functionality of (2) is completely covered by (3), therefore -(2) should be removed. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Bill believes the extra assignment operators are necessary for resolving -ambiguities, but that does not mean it needs to be part of the specification. -</p> -<p> -Move to Open. -We recommend this be looked at in the context of the ongoing work -related to the pair templates. -</p> -</blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Leave this open pending the removal of concepts from the WD. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD, see issue <a href="lwg-defects.html#801">801</a>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<ol style="list-style-type:upper-alpha"> -<li> -<p> -In 20.3 [pairs] p. 1, class <tt>pair</tt> and just before p. 13 remove the declaration: -</p> - -<blockquote><pre> -requires MoveAssignable<T1> && MoveAssignable<T2> pair& operator=(pair&& p ); -</pre></blockquote> -</li> - -<li> -Remove p.13+p.14 -</li> - -</ol> - - - - - -<hr> -<h3><a name="917"></a>917. Redundant move-assignment operator of <tt>tuple</tt> should be removed</h3> -<p><b>Section:</b> 20.4.2.1 [tuple.cnstr] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2008-10-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#tuple.cnstr">active issues</a> in [tuple.cnstr].</p> -<p><b>View all other</b> <a href="lwg-index.html#tuple.cnstr">issues</a> in [tuple.cnstr].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>see also <a href="lwg-closed.html#916">916</a>.</b></p> -<p> -N2770 (and thus now the WP) removed the -non-template move-assignment operator from tuple's class definition, -but the latter individual member description does still provide this -operator. Is this (a) an oversight and can it (b) be solved as part of an -editorial process? -</p> - -<p><i>[ -Post Summit Daniel provided wording. -]</i></p> - - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We believe that the proposed resolution's part 1 is editorial. -</p> -<p> -Regarding part 2, we either remove the specification as proposed, -or else add back the declaration to which the specification refers. -Alisdair and Bill prefer the latter. -It is not immediately obvious whether the function is intended to be present. -</p> -<p> -We recommend that the Project Editor restore the missing declaration -and that we keep part 2 of the issue alive. -</p> -<p> -Move to Open. -</p> -</blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Leave this open pending the removal of concepts from the WD. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD, see issue <a href="lwg-defects.html#801">801</a>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -<p> -In 20.4.2 [tuple.tuple], class <tt>tuple</tt> just before member <tt>swap</tt> please -change as indicated: -</p> -<p><i>[ -This fixes an editorial loss between N2798 to N2800 -]</i></p> - -<blockquote><pre> -template <class... UTypes> -requires HasAssign<Types, const UTypes&>... -<ins>tuple& operator=(const pair<UTypes...>&);</ins> - -template <class... UTypes> -requires HasAssign<Types, RvalueOf<UTypes>::type>... -<ins>tuple& operator=(pair<UTypes...>&&);</ins> -</pre></blockquote> -</li> -<li> -<p> -In 20.4.2.1 [tuple.cnstr], starting just before p. 11 please remove -as indicated: -</p> - -<blockquote><pre> -<del>requires MoveAssignable<Types>... tuple& operator=(tuple&& u);</del> -</pre> -<blockquote> -<p> -<del>-11- <i>Effects:</i> Move-assigns each element of <tt>u</tt> to the corresponding -element of <tt>*this</tt>.</del> -</p> -<p> -<del>-12- <i>Returns:</i> <tt>*this</tt>.</del> -</p> -</blockquote> -</blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="918"></a>918. Swap for tuple needs to be conceptualized</h3> -<p><b>Section:</b> 20.4.2.3 [tuple.swap] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2008-10-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Issue <a href="lwg-defects.html#522">522</a> was accepted after <tt>tuple</tt> had been conceptualized, -therefore this step needs to be completed. -</p> - -<p><i>[ -Post Summit Daniel adds -]</i></p> - - -<blockquote><p> -This is now NAD Editorial (addressed by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2844.html">N2844</a>) -except for item 3 in the proposed wording. -</p></blockquote> - -<p><i>[ -2009-05-01 Daniel adds: -]</i></p> - - -<blockquote><p> -As of the recent WP -(<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2857.pdf">N2857</a>), -this issue is now completely covered by editorial changes (including the third bullet), -therefore I unconditionally recommend NAD. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We observed that all the proposed changes have already been applied to the -Working Draft, rendering this issue moot. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -<p> -In both 20.4.1 [tuple.general]/2 and 20.4.2.9 [tuple.special] change -</p> - -<blockquote><pre> -template <<del>class</del> <ins>Swappable</ins>... Types> -void swap(tuple<Types...>& x, tuple<Types...>& y); -</pre></blockquote> - -</li> - -<li> -<p> -In 20.4.2 [tuple.tuple], class <tt>tuple</tt> definition and in -20.4.2.3 [tuple.swap], change -</p> - -<blockquote><pre> -<ins>requires Swappable<Types>...</ins>void swap(tuple&); -</pre></blockquote> - -</li> - -<li> -<p> -In 20.4.2.3 [tuple.swap] remove the current requires-clause, which says: -</p> - -<blockquote><p> -<del><i>Requires:</i> Each type in <tt>Types</tt> shall be <tt>Swappable</tt></del> -</p></blockquote> -</li> - -</ol> - - - - - - -<hr> -<h3><a name="919"></a>919. (forward_)list specialized remove algorithms are over constrained</h3> -<p><b>Section:</b> 23.3.4.6 [forwardlist.ops], 23.3.5.5 [list.ops] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2008-10-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#forwardlist.ops">issues</a> in [forwardlist.ops].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The signatures of <tt>forwardlist::remove</tt> and <tt>list::remove</tt> -defined in 23.3.4.6 [forwardlist.ops] before 11 + 23.3.5.5 [list.ops] before 15: -</p> - -<blockquote><pre> -requires EqualityComparable<T> void remove(const T& value); -</pre></blockquote> - -<p> -are asymmetric to their predicate variants (which only require -<tt>Predicate</tt>, <em>not</em> <tt>EquivalenceRelation</tt>) and with the free algorithm -remove (which only require <tt>HasEqualTo</tt>). Also, nothing in the -pre-concept WP -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2723.pdf">N2723</a> -implies that <tt>EqualityComparable</tt> should -be the intended requirement. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree with the proposed resolution, -but would like additional input from concepts experts. -</p> -<p> -Move to Review. -</p> -</blockquote> - -<p><i>[ -2009-07-21 Alisdair adds: -]</i></p> - - -<blockquote><p> -Current rationale and wording for this issue is built around concepts. I -suggest the issue reverts to Open status. I believe there is enough of -an issue to review after concepts are removed from the WP to re-examine -the issue in Santa Cruz, rather than resolve as NAD Concepts. -</p></blockquote> - -<p><i>[ -2009-10-10 Daniel adds: -]</i></p> - - -<blockquote><p> -Recommend NAD: The concept-free wording as of -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2960.pdf">N2960</a> -has no longer the -over-specified requirement -<tt>EqualityComparable</tt> for the remove function that uses <tt>==</tt>. In fact, now -the same test conditions exists -as for the free algorithm <tt>remove</tt> (25.3.8 [alg.remove]). The error was -introduced in the process of conceptifying. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -NAD, solved by the removal of concepts. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<ol style="list-style-type:upper-alpha"> -<li> -<p> -Replace in 23.3.4.6 [forwardlist.ops] before 11 and in 23.3.5.5 [list.ops] before 15 -</p> - -<blockquote><pre> -requires <del>EqualityComparable<T></del> <ins>HasEqualTo<T, T></ins> void remove(const T& value); -</pre></blockquote> -</li> -</ol> - - - - - - -<hr> -<h3><a name="926"></a>926. Sequentially consistent fences, relaxed operations and modification order</h3> -<p><b>Section:</b> 29.3 [atomics.order] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Anthony Williams <b>Opened:</b> 2008-10-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#atomics.order">active issues</a> in [atomics.order].</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.order">issues</a> in [atomics.order].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses UK 313</b></p> - -<p> -There was an interesting issue raised over on comp.programming.threads -today regarding the following example -</p> - -<blockquote><pre> -// Thread 1: -x.store(1, memory_order_relaxed); // SX -atomic_thread_fence(memory_order_seq_cst); // F1 -y.store(1, memory_order_relaxed); // SY1 -atomic_thread_fence(memory_order_seq_cst); // F2 -r1 = y.load(memory_order_relaxed); // RY - -// Thread 2: -y.store(0, memory_order_relaxed); // SY2 -atomic_thread_fence(memory_order_seq_cst); // F3 -r2 = x.load(memory_order_relaxed); // RX -</pre></blockquote> - -<p> -is the outcome <tt>r1 == 0</tt> and <tt>r2 == 0</tt> possible? -</p> -<p> -I think the intent is that this is not possible, but I am not sure the -wording guarantees that. Here is my analysis: -</p> -<p> -Since all the fences are SC, there must be a total order between them. -<tt>F1</tt> must be before <tt>F2</tt> in that order since they are in -the same thread. Therefore <tt>F3</tt> is either before <tt>F1</tt>, -between <tt>F1</tt> and <tt>F2</tt> or after <tt>F2</tt>. -</p> -<p> -If <tt>F3</tt> is <em>after</em> <tt>F2</tt>, then we can apply 29.3 [atomics.order]p5 from -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2798.pdf">N2798</a>: -</p> - -<blockquote><p> -For atomic operations <tt>A</tt> and <tt>B</tt> on an atomic object -<tt>M</tt>, where <tt>A</tt> modifies <tt>M</tt> and <tt>B</tt> takes -its value, if there are <tt>memory_order_seq_cst</tt> fences <tt>X</tt> -and <tt>Y</tt> such that <tt>A</tt> is sequenced before <tt>X</tt>, -<tt>Y</tt> is sequenced before <tt>B</tt>, and <tt>X</tt> precedes -<tt>Y</tt> in <tt>S</tt>, then <tt>B</tt> observes either the effects of -<tt>A</tt> or a later modification of <tt>M</tt> in its modification -order. -</p></blockquote> - -<p> -In this case, <tt>A</tt> is <tt>SX</tt>, <tt>B</tt> is <tt>RX</tt>, the -fence <tt>X</tt> is <tt>F2</tt> and the fence <tt>Y</tt> is <tt>F3</tt>, -so <tt>RX</tt> must see 1. -</p> -<p> -If <tt>F3</tt> is <em>before</em> <tt>F2</tt>, this doesn't apply, but -<tt>F3</tt> can therefore be before or after <tt>F1</tt>. -</p> -<p> -If <tt>F3</tt> is <em>after</em> <tt>F1</tt>, the same logic applies, but this -time the fence <tt>X</tt> is <tt>F1</tt>. Therefore again, <tt>RX</tt> -must see 1. -</p> -<p> -Finally we have the case that <tt>F3</tt> is <em>before</em> <tt>F1</tt> -in the SC ordering. There are now no guarantees about <tt>RX</tt>, and -<tt>RX</tt> can see <tt>r2==0</tt>. -</p> -<p> -We can apply 29.3 [atomics.order]p5 again. This time, -<tt>A</tt> is <tt>SY2</tt>, <tt>B</tt> is <tt>RY</tt>, <tt>X</tt> is -<tt>F3</tt> and <tt>Y</tt> is <tt>F1</tt>. Thus <tt>RY</tt> must observe -the effects of <tt>SY2</tt> or a later modification of <tt>y</tt> in its -modification order. -</p> -<p> -Since <tt>SY1</tt> is sequenced before <tt>RY</tt>, <tt>RY</tt> must -observe the effects of <tt>SY1</tt> or a later modification of -<tt>y</tt> in its modification order. -</p> -<p> -In order to ensure that <tt>RY</tt> sees <tt>(r1==1)</tt>, we must see -that <tt>SY1</tt> is later in the modification order of <tt>y</tt> than -<tt>SY2</tt>. -</p> -<p> -We're now skating on thin ice. Conceptually, <tt>SY2</tt> happens-before -<tt>F3</tt>, <tt>F3</tt> is SC-ordered before <tt>F1</tt>, <tt>F1</tt> -happens-before <tt>SY1</tt>, so <tt>SY1</tt> is later in the -modification order <tt>M</tt> of <tt>y</tt>, and <tt>RY</tt> must see -the result of <tt>SY1</tt> (<tt>r1==1</tt>). However, I don't think the -words are clear on that. -</p> - -<p><i>[ -Post Summit Hans adds: -]</i></p> - - -<blockquote> -<p> -In my (Hans') view, our definition of fences will always be weaker than -what particular hardware will guarantee. <tt>Memory_order_seq_cst</tt> fences -inherently don't guarantee sequential consistency anyway, for good -reasons (e.g. because they can't enforce a total order on stores). - Hence I don't think the issue demonstrates a gross failure to achieve -what we intended to achieve. The example in question is a bit esoteric. - Hence, in my view, living with the status quo certainly wouldn't be a -disaster either. -</p> -<p> -In any case, we should probably add text along the lines of the -following between p5 and p6 in 29.3 [atomics.order]: -</p> -<blockquote><p> -[Note: <tt>Memory_order_seq_cst</tt> only ensures sequential consistency for a -data-race-free program that uses exclusively <tt>memory_order_seq_cst</tt> -operations. Any use of weaker ordering will invalidate this guarantee -unless extreme care is used. In particular, <tt>memory_order_seq_cst</tt> fences -only ensure a total order for the fences themselves. They cannot, in -general, be used to restore sequential consistency for atomic operations -with weaker ordering specifications.] -</p></blockquote> - -<p> -Also see thread beginning at c++std-lib-23271. -</p> - -</blockquote> - -<p><i>[ -Herve's correction: -]</i></p> - -<blockquote> -<p> -Minor point, and sorry for the knee jerk reaction: I admit to having -no knowledge of Memory_order_seq_cst, but my former boss (John Lakos) -has ingrained an automatic introspection on the use of "only". I -think you meant: -</p> - -<blockquote><p> -[Note: <tt>Memory_order_seq_cst</tt> ensures sequential consistency only -for . . . . In particular, <tt>memory_order_seq_cst</tt> fences ensure a -total order only for . . . -</p></blockquote> -<p> -Unless, of course, <tt>Memory_order_seq_cst</tt> really do nothing but ensure -sequential consistency for a data-race-free program that uses -exclusively <tt>memory_order_seq_cst</tt> operations. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -NAD Editorial. Solved by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2992.html">N2992</a>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add a new paragraph after 29.3 [atomics.order]p5 that says -</p> - -<blockquote><p> -For atomic operations <tt>A</tt> and <tt>B</tt> on an atomic object -<tt>M</tt>, where <tt>A</tt> and <tt>B</tt> modify <tt>M</tt>, if there -are <tt>memory_order_seq_cst</tt> fences <tt>X</tt> and <tt>Y</tt> such -that <tt>A</tt> is sequenced before <tt>X</tt>, <tt>Y</tt> is sequenced -before <tt>B</tt>, and <tt>X</tt> precedes <tt>Y</tt> in <tt>S</tt>, -then <tt>B</tt> occurs later than <tt>A</tt> in the modifiction order of -<tt>M</tt>. -</p></blockquote> - - - - - -<hr> -<h3><a name="927"></a>927. <tt>Dereferenceable</tt> should be <tt>HasDereference</tt></h3> -<p><b>Section:</b> X [allocator.concepts] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Pablo Halpern <b>Opened:</b> 2008-10-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -X [allocator.concepts] contains a reference to a concept named -<tt>Dereferenceable</tt>. No such concept exists. -</p> - -<p><i>[ -Daniel adds 2009-02-14: -]</i></p> - - -<blockquote><p> -The proposal given in the paper -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2829.pdf">N2829</a> -would automatically resolve this issue. -</p></blockquote> - - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -This particular set of changes has already been made. -There are two related changes later on (and possibly also an earlier Example); -these can be handled editorially. -</p> -<p> -Move to NAD Editorial. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change all uses of the concept <tt>Dereferenceable</tt> to -<tt>HasDereference</tt> in X [allocator.concepts]. -</p> - - - - - -<hr> -<h3><a name="928"></a>928. Wrong concepts used for <tt>tuple</tt>'s comparison operators</h3> -<p><b>Section:</b> 20.4.2.7 [tuple.rel] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Joe Gottman <b>Opened:</b> 2008-10-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#tuple.rel">active issues</a> in [tuple.rel].</p> -<p><b>View all other</b> <a href="lwg-index.html#tuple.rel">issues</a> in [tuple.rel].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In the latest working draft for C++0x, <tt>tuple</tt>'s <tt>operator==</tt> and <tt>operator<</tt> -are declared as -</p> - -<blockquote><pre> -template<class... TTypes, class... UTypes> - requires EqualityComparable<TTypes, UTypes>... - bool operator==(const tuple<TTypes...>& t, const tuple<UTypes...>& u); -</pre></blockquote> - -<p> -and -</p> - -<blockquote><pre> -template<class... TTypes, class... UTypes> - requires LessThanComparable<TTypes, UTypes>... - bool operator<(const tuple<TTypes...>& t, const tuple<UTypes...>& u); -</pre></blockquote> - -<p> -But the concepts <tt>EqualityComparable</tt> and <tt>LessThanComparable</tt> only take one -parameter, not two. Also, even if <tt>LessThanComparable</tt> could take two -parameters, the definition of <tt>tuple::operator<()</tt> should also require -</p> - -<blockquote><pre> -LessThanComparable<UTypes, TTypes>... // (note the order) -</pre></blockquote> - -<p> -since the algorithm for <tt>tuple::operator<</tt> is the following (pseudo-code) -</p> - -<blockquote><pre> -for (size_t N = 0; N < sizeof...(TTypes); ++N) { - if (get<N>(t) < get<N>(u) return true; - else if ((get<N>(u) < get<N>(t)) return false; -} - -return false; -</pre></blockquote> - -<p> -Similar problems hold for <tt>tuples</tt>'s other comparison operators. -</p> - -<p><i>[ -Post Summit: -]</i></p> - - -<blockquote><p> -Recommend Tentatively Ready. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -In 20.4.1 [tuple.general] and 20.4.2.7 [tuple.rel] change: -</p> - -<blockquote><pre> -template<class... TTypes, class... UTypes> - requires <del>EqualityComparable</del><ins>HasEqualTo</ins><TTypes, UTypes>... - bool operator==(const tuple<TTypes...>&, const tuple<UTypes...>&); - -template<class... TTypes, class... UTypes> - requires <del>LessThanComparable</del><ins>HasLess</ins><TTypes, UTypes>... <ins>&& HasLess<UTypes, TTypes>...</ins> - bool operator<(const tuple<TTypes...>&, const tuple<UTypes...>&); - -template<class... TTypes, class... UTypes> - requires <del>EqualityComparable</del><ins>HasEqualTo</ins><TTypes, UTypes>... - bool operator!=(const tuple<TTypes...>&, const tuple<UTypes...>&); - -template<class... TTypes, class... UTypes> - requires <del>LessThanComparable</del><ins>HasLess</ins><<del>U</del><ins>T</ins>Types, <del>T</del><ins>U</ins>Types>... <ins>&& HasLess<UTypes, TTypes>...</ins> - bool operator>(const tuple<TTypes...>&, const tuple<UTypes...>&); - -template<class... TTypes, class... UTypes> - requires <del>LessThanComparable</del><ins>HasLess</ins><<del>U</del><ins>T</ins>Types, <del>T</del><ins>U</ins>Types>... <ins>&& HasLess<UTypes, TTypes>...</ins> - bool operator<=(const tuple<TTypes...>&, const tuple<UTypes...>&); - -template<class... TTypes, class... UTypes> - requires <del>LessThanComparable</del><ins>HasLess</ins><TTypes, UTypes>... <ins>&& HasLess<UTypes, TTypes>...</ins> - bool operator>=(const tuple<TTypes...>&, const tuple<UTypes...>&); -</pre></blockquote> - - - - - -<hr> -<h3><a name="930"></a>930. Access to std::array data as built-in array type</h3> -<p><b>Section:</b> 23.3.2 [array] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Niels Dekker <b>Opened:</b> 2008-11-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#array">active issues</a> in [array].</p> -<p><b>View all other</b> <a href="lwg-index.html#array">issues</a> in [array].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -The Working Draft (N2798) allows access to the elements of -<tt>std::array</tt> by its <tt>data()</tt> member function: -</p> - -<blockquote> - -<h5>23.2.1.4 array::data [array.data]</h5> -<pre> - T *data(); - const T *data() const; -</pre> -<ol><li> - Returns: elems. -</li></ol> -</blockquote> - -<p> -Unfortunately, the result of <tt>std::array::data()</tt> cannot be bound -to a reference to a built-in array of the type of <tt>array::elems</tt>. -And <tt>std::array</tt> provides no other way to get a reference to -<tt>array::elems</tt>. -This hampers the use of <tt>std::array</tt>, for example when trying to -pass its data to a C style API function: -</p> - -<pre> - // Some C style API function. - void set_path( char (*)[MAX_PATH] ); - - std::array<char,MAX_PATH> path; - set_path( path.data() ); // error - set_path( &(path.data()) ); // error -</pre> - - <p> -Another example, trying to pass the array data to an instance of another -C++ class: -</p> - -<pre> - // Represents a 3-D point in space. - class three_d_point { - public: - explicit three_d_point(const double (&)[3]); - }; - - const std::array<double,3> coordinates = { 0, 1, 2 }; - three_d_point point1( coordinates.data() ); // error. - three_d_point point2( *(coordinates.data()) ); // error. -</pre> - -<p> -A user might be tempted to use <tt>std::array::elems</tt> instead, but -doing so isn't recommended, because <tt>std::array::elems</tt> is "for -exposition only". Note that Boost.Array users might already use -<tt>boost::array::elems</tt>, as its documentation doesn't explicitly -state that <tt>boost::array::elems</tt> is for exposition only: -http://www.boost.org/doc/libs/1_36_0/doc/html/boost/array.html -</p> -<p> -I can think of three options to solve this issue: -</p> -<ol><li> -Remove the words "exposition only" from the definition of -<tt>std::array::elems</tt>, as well as the note saying that "elems is -shown for exposition only." -</li><li> -Change the signature of <tt>std::array::data()</tt>, so that it would -return a reference to the built-in array, instead of a pointer to its -first element. -</li><li> -Add extra member functions, returning a reference to the built-in array. -</li></ol> -<p> -Lawrence Crowl wrote me that it might be better to leave -<tt>std::array::elems</tt> "for exposition only", to allow alternate -representations to allocate the array data dynamically. This might be -of interest to the embedded community, having to deal with very limited -stack sizes. -</p> -<p> -The second option, changing the return type of -<tt>std::array::data()</tt>, would break backward compatible to current -Boost and TR1 implementations, as well as to the other contiguous -container (<tt>vector</tt> and <tt>string</tt>) in a very subtle way. -For example, the following call to <tt>std::swap</tt> currently swap two -locally declared pointers <tt>(data1, data2)</tt>, for any container -type <tt>T</tt> that has a <tt>data()</tt> member function. When -<tt>std::array::data()</tt> is changed to return a reference, the -<tt>std::swap</tt> call may swap the container elements instead. -</p> - -<pre> - template <typename T> - void func(T& container1, T& container2) - { - // Are data1 and data2 pointers or references? - auto data1 = container1.data(); - auto data2 = container2.data(); - - // Will this swap two local pointers, or all container elements? - std::swap(data1, data2); - } -</pre> - -<p> -The following concept is currently satisfied by all contiguous -containers, but it no longer is for <tt>std::array</tt>, when -<tt>array::data()</tt> -is changed to return a reference (tested on ConceptGCC Alpha 7): -</p> - -<pre> - auto concept ContiguousContainerConcept<typename T> - { - typename value_type = typename T::value_type; - const value_type * T::data() const; - } -</pre> - -<p> -Still it's worth considering having <tt>std::array::data()</tt> return a -reference, because it might be the most intuitive option, from a user's -point of view. Nicolai Josuttis (who wrote <tt>boost::array</tt>) -mailed me that he very much prefers this option. -</p> -<p> -Note that for this option, the definition of <tt>data()</tt> would also -need to be revised for zero-sized arrays, as its return type cannot be a -reference to a zero-sized built-in array. Regarding zero-sized array, -<tt>data()</tt> could throw an exception. Or there could be a partial -specialization of <tt>std::array</tt> where <tt>data()</tt> returns -<tt>T*</tt> or gets removed. -</p> -<p> -Personally I prefer the third option, adding a new member function to -<tt>std::array</tt>, overloaded for const and non-const access, -returning a reference to the built-in array, to avoid those compatible -issues. I'd propose naming the function <tt>std::array::c_array()</tt>, -which sounds intuitive to me. Note that <tt>boost::array</tt> already -has a <tt>c_array()</tt> member, returning a pointer, but Nicolai told -me that this one is only there for historical reasons. (Otherwise a name -like <tt>std::array::native_array()</tt> or -<tt>std::array::builtin_array()</tt> would also be fine with me.) -According to my proposed resolution, a zero-sized <tt>std::array</tt> does not need -to have <tt>c_array()</tt>, while it is still required to have -<tt>data()</tt> functions. -</p> - -<p><i>[ -Post Summit: -]</i></p> - - -<blockquote> - -<p> -Alisdair: Don't like p4 suggesting implementation-defined behaviour. -</p> -<p> -Walter: What about an explicit conversion operator, instead of adding -the new member function? -</p> -<p> -Alisdair: Noodling about: -</p> -<blockquote><pre> -template<size_t N, ValueType T> -struct array -{ - T elems[N]; - -// fantasy code starts here - -// crazy decltype version for grins only -//requires True<(N>0)> -//explict operator decltype(elems) & () { return elems; } - -// conversion to lvalue ref -requires True<(N>0)> -explict operator T(&)[N] () & { return elems; } - -// conversion to const lvalue ref -requires True<(N>0)> -explict operator const T(&)[N] () const & { return elems; } - -// conversion to rvalue ref using ref qualifiers -requires True<(N>0)> -explict operator T(&&)[N] () && { return elems; } - -// fantasy code ends here - -explicit operator bool() { return true; } -}; -</pre></blockquote> - -<p> -This seems legal but odd. Jason Merrill says currently a CWG issue 613 -on the non-static data member that fixes the error that current G++ -gives for the non-explicit, non-conceptualized version of this. Verdict -from human compiler: seems legal. -</p> -<p> -Some grumbling about zero-sized arrays being allowed and supported. -</p> -<p> -Walter: Would this address the issue? Are we inclined to go this route? -</p> -<p> -Alan: What would usage look like? -</p> -<blockquote><pre> -// 3-d point in space -struct three_d_point -{ - explicit three_d_point(const double (&)[3]); -}; - -void sink(double*); - -const std::array<double, 3> coordinates = { 0, 1, 2 }; -three_d_point point1( coordinates.data() ); //error -three_d_point point2( *(coordinates.data()) ); // error -three_d_point point3( coordinates ); // yay! - -sink(cooridinates); // error, no conversion -</pre></blockquote> - -<p> -Recommended Open with new wording. Take the required clause and add the -explicit conversion operators, not have a <tt>typedef</tt>. At issue still is use -<tt>decltype</tt> or use <tt>T[N]</tt>. In favour of using <tt>T[N]</tt>, even though use of -<tt>decltype</tt> is specially clever. -</p> - -</blockquote> - -<p><i>[ -Post Summit, further discussion in the thread starting with c++std-lib-23215. -]</i></p> - - -<p><i>[ -2009-07 post-Frankfurt (Saturday afternoon group): -]</i></p> - - -<blockquote> -<p> -The idea to resolve the issue by adding explicit conversion operators -was abandoned, because it would be inconvenient to use, especially when -passing the array to a template function, as mentioned by Daniel. So we -reconsidered the original proposed resolution, which appeared -acceptable, except for its proposed changes to 23.3.2.8 [array.zero], which -allowed <tt>c_array_type</tt> and <tt>c_array()</tt> to be absent for a zero-sized array. -Alisdair argued that such wording would disallow certain generic use -cases. New wording for 23.3.2.8 [array.zero] was agreed upon (Howard: and -is reflected in the proposed resolution). -</p> -<p> -Move to Review -</p> -</blockquote> - -<p><i>[ -2009-07-31 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -I will be unhappy voting the proposed resolution for 930 past review -until we have implementation experience with reference qualifiers. -Specifically, I want to understand the impact of the missing overload -for <tt>const &&</tt> (if any.) -</p> - -<p> -If we think the issue is important enough it might be worthwhile -stripping the ref qualifiers for easy progress next meeting, and opening -yet another issue to put them back with experience. -</p> - -<p> -Recommend deferring any decision on splitting the issue until we get LWG -feedback next meeting - I may be the lone dissenting voice if others are -prepared to proceed without it. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD. There was not enough consensus that this was sufficiently -useful. There are known other ways to do this, such as small inline -conversion functions. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add to the template definition of array, 23.3.2 [array]/3: -</p> - -<blockquote> -<pre><ins> -typedef T c_array_type[N]; -c_array_type & c_array() &; -c_array_type && c_array() &&; -const c_array_type & c_array() const &; -</ins> -</pre> -</blockquote> - -<p> -Add the following subsection to 23.3.2 [array], after 23.3.2.5 [array.data]: -</p> - -<blockquote> -<h5><ins>23.2.1.5 array::c_array [array.c_array]</ins></h5> - <pre><ins> -c_array_type & c_array() &; -c_array_type && c_array() &&; -const c_array_type & c_array() const &; -</ins></pre> -<blockquote> -<p> -<ins><i>Returns:</i> <tt>elems</tt>.</ins> -</p> -</blockquote> - -</blockquote> - - - -<p> -Change Zero sized arrays 23.3.2.8 [array.zero]: -</p> - -<blockquote> - -<p>-2- ...</p> - -<p><ins> -The type <tt>c_array_type</tt> is unspecified for a zero-sized array. -</ins></p> - -<p> --3- The effect of calling <ins><tt>c_array()</tt>,</ins> <tt>front()</tt><ins>,</ins> or -<tt>back()</tt> for a zero-sized array is implementation defined. -</p> -</blockquote> - - - - - - -<hr> -<h3><a name="937"></a>937. Atomics for standard typedef types</h3> -<p><b>Section:</b> 29 [atomics] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Clark Nelson <b>Opened:</b> 2008-12-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics">issues</a> in [atomics].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US 89</b></p> - -<blockquote> -<p> -The types in the table "Atomics for standard typedef types" should be -typedefs, not classes. These semantics are necessary for compatibility -with C. -</p> - -<p> -Change the classes to typedefs. -</p> -</blockquote> - -<p> -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2427.html">N2427</a> -specified different requirements for atomic analogs of fundamental -integer types (such as <tt>atomic_int</tt>) and for atomic analogs of <tt><cstdint></tt> -typedefs (such as <tt>atomic_size_t</tt>). Specifically, <tt>atomic_int</tt> et al. were -specified to be distinct classes, whereas <tt>atomic_size_t</tt> et al. were -specified to be typedefs. Unfortunately, in applying -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2427.html">N2427</a> -to the WD, that distinction was erased, and the atomic analog of every <tt><cstdint></tt> -typedef is required to be a distinct class. -</p> - -<p> -It shouldn't be required that the atomic analog of every <tt><cstdint></tt> -typedef be a typedef for some fundamental integer type. After all, -<tt><cstdint></tt> is supposed to provide standard names for extended integer -types. So there was a problem in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2427.html">N2427</a>, -which certainly could have been -interpreted to require that. But the status quo in the WD is even worse, -because it's unambiguously wrong. -</p> - -<p> -What is needed are words to require the existence of a bunch of type -names, without specifying whether they are class names or typedef names. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote> -<p> -Change status to NAD, editorial. See US 89 comment notes above. -</p> -<p> -Direct the editor to turn the types into typedefs as proposed in the -comment. Paper approved by committee used typedefs, this appears to have -been introduced as an editorial change. Rationale: for compatibility -with C. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="941"></a>941. Ref-qualifiers for assignment operators</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Niels Dekker <b>Opened:</b> 2008-12-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The assignment and equality operators <tt>=</tt> and <tt>==</tt> are easily confused, just -because of their visual similarity, and in this case a simple typo can cause -a serious bug. When the left side of an <tt>operator=</tt> is an rvalue, it's -highly unlikely that the assignment was intended by the programmer: -</p> -<blockquote><pre> -if ( func() = value ) // Typical typo: == intended! -</pre></blockquote> -<p> -Built-in types don't support assignment to an rvalue, but unfortunately, -a lot of types provided by the Standard Library do. -</p> -<p> -Fortunately the language now offers a syntax to prevent a certain member -function from having an rvalue as <tt>*this</tt>: by adding a ref-qualifier (<tt>&</tt>) -to the member function declaration. Assignment operators are explicitly -mentioned as a use case of ref-qualifiers, in "Extending Move Semantics -To <tt>*this</tt> (Revision 1)", -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1821.htm">N1821</a> by Daveed -Vandevoorde and Bronek Kozicki -</p> -<p> -Hereby I would like to propose adding ref-qualifiers to all appropriate -assignment operators in the library. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to Open. -We recommend this be deferred until after the next Committee Draft. -</p></blockquote> - -<p><i>[ -Frankfurt 2009-07: -]</i></p> - - -<blockquote> -<p> -The LWG declined to move forward with -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2819.html">N2819</a>. -</p> -<p> -Moved to NAD. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -A proposed resolution is provided by the paper on this subject, -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2819.html">N2819</a>, -<i>Ref-qualifiers for assignment operators of the Standard Library</i> -</p> - - - - - -<hr> -<h3><a name="942"></a>942. Atomics synopsis typo</h3> -<p><b>Section:</b> 29 [atomics] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Holger Grund <b>Opened:</b> 2008-12-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics">issues</a> in [atomics].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#880">880</a></p> -<p><b>Discussion:</b></p> - - - -<p> -I'm looking at 29 [atomics] and can't really make sense of a couple of things. -</p> -<p> -Firstly, there appears to be a typo in the <tt><cstdatomic></tt> synopsis: -</p> - -<blockquote> -<p> -The <tt>atomic_exchange</tt> overload taking an <tt>atomic_address</tt> -is missing the second parameter: -</p> - -<blockquote><pre> -void* atomic_exchange(volatile atomic_address*); -</pre></blockquote> - -<p> -should be -</p> - -<blockquote><pre> -void* atomic_exchange(volatile atomic_address*<ins>, void*</ins>); -</pre></blockquote> - -<p> -Note, that this is <em>not</em> covered by <a href="lwg-defects.html#880">880</a> "Missing atomic exchange parameter", -which only talks about the <tt>atomic_bool</tt>. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change the synopsis in 29 [atomics]/2: -</p> - -<blockquote><pre> -void* atomic_exchange(volatile atomic_address*<ins>, void*</ins>); -</pre></blockquote> - - - - - - -<hr> -<h3><a name="945"></a>945. <tt>system_clock::rep</tt> not specified</h3> -<p><b>Section:</b> 20.12.7.1 [time.clock.system] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2008-12-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#time.clock.system">issues</a> in [time.clock.system].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In 20.12.7.1 [time.clock.system], the declaration of <tt>system_clock::rep</tt> says "see -below", but there is nothing below that describes it. -</p> - -<p><i>[ -Howard adds: -]</i></p> - - -<blockquote> -<p> -This note refers to: -</p> - -<blockquote><p> --2- <tt>system_clock::duration::min() < system_clock::duration::zero()</tt> shall be <tt>true</tt>. -</p></blockquote> - -<p> -I.e. this is standardeze for "<tt>system_clock::rep</tt> is signed". -Perhaps an editorial note along the lines of: -</p> - -<blockquote><p> --2- <tt>system_clock::duration::min() < system_clock::duration::zero()</tt> -shall be <tt>true</tt>. <ins>[<i>Note:</i> <tt>system_clock::rep</tt> shall be signed. <i>-- end note</i>].</ins> -</p></blockquote> - -<p> -? -</p> - -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the direction of the proposed resolution. -Move to NAD Editorial. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add a note to 20.12.7.1 [time.clock.system], p2: -</p> -<blockquote><p> --2- <tt>system_clock::duration::min() < system_clock::duration::zero()</tt> -shall be <tt>true</tt>. <ins>[<i>Note:</i> <tt>system_clock::rep</tt> shall be signed. <i>-- end note</i>].</ins> -</p></blockquote> - - - - - -<hr> -<h3><a name="946"></a>946. <tt>duration_cast</tt> improperly specified</h3> -<p><b>Section:</b> 20.12.5.7 [time.duration.cast] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2008-12-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#time.duration.cast">issues</a> in [time.duration.cast].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -20.12.5.7 [time.duration.cast]/3: -</p> -<blockquote><p> -.... All intermediate computations shall be -carried out in the widest possible representation... . -</p></blockquote> - -<p> -So ignoring floating-point types for the moment, all this arithmetic has to be done -using the implementation's largest integral type, even if both arguments -use <tt>int</tt> for their representation. This seems excessive. And it's not at -all clear what this means if we don't ignore floating-point types. -</p> - -<p> -This issue is related to <a href="lwg-closed.html#952">952</a>. -</p> - -<p><i>[ -Howard adds: -]</i></p> - - -<blockquote> -<p> -The intent of this remark is that intermediate computations are carried out -using: -</p> - -<blockquote><pre> -common_type<typename ToDuration::rep, Rep, intmax_t>::type -</pre></blockquote> - -<p> -The Remark was intended to be clarifying prose supporting the rather algorithmic description -of the previous paragraph. I'm open to suggestions. Perhaps the entire paragraph -3 (Remarks) would be better dropped? -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We view this as a specific case of issue <a href="lwg-closed.html#952">952</a>, -and should be resolved when that issue is resolved. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="952"></a>952. Various threading bugs #2</h3> -<p><b>Section:</b> 20.12.5.7 [time.duration.cast] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2009-01-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#time.duration.cast">issues</a> in [time.duration.cast].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -20.12.5.7 [time.duration.cast] specifies an implementation and imposes -requirements in text (and the implementation doesn't satisfy all of the -text requirements). Pick one. -</p> - -<p> -This issue is related to <a href="lwg-closed.html#946">946</a>. -</p> - -<p><i>[ -2009-05-10 Howard adds: -]</i></p> - - -<blockquote> -<p> -The <i>Remarks</i> paragraph is an English re-statement of the preceeding -<i>Returns</i> clause. It was meant to be clarifying and motivating, not -confusing. I'm not aware with how the <i>Remarks</i> contradicts the <i>Returns</i> clause -but I'm ok with simply removing the <i>Remarks</i>. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Pete suggests that this could be resolved -by rephrasing the Remarks to Notes. -</p> -<p> -Move to NAD Editorial. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="955"></a>955. Various threading bugs #5</h3> -<p><b>Section:</b> 20.12.3 [time.clock.req] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2009-01-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#time.clock.req">issues</a> in [time.clock.req].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -20.12.3 [time.clock.req] requires that a clock type have a member -typedef named <tt>time_point</tt> that names an instantiation of the -template <tt>time_point</tt>, and a member named <tt>duration</tt> that -names an instantiation of the template <tt>duration</tt>. This mixing of -levels is confusing. The typedef names should be different from the -template names. -</p> - -<p><i>[ -Post Summit, Anthony provided proposed wording. -]</i></p> - - -<p><i>[ -2009-05-04 Howard adds: -]</i></p> - - -<blockquote> -<p> -The reason that the typedef names were given the same name as the class templates -was so that clients would not have to stop and think about whether they were -using the clock's native <tt>time_point</tt> / <tt>duration</tt> or the class -template directly. In this case, one person's confusion is another person's -encapsulation. The detail that sometimes one is referring to the clock's -native types, and sometimes one is referring to an independent type is -<em>purposefully</em> "hidden" because it is supposed to be an unimportant -detail. It can be confusing to have to remember when to type <tt>duration</tt> -and when to type <tt>duration_type</tt>, and there is no need to require the -client to remember something like that. -</p> - -<p> -For example, here is code that I once wrote in testing out the usability of -this facility: -</p> - -<blockquote><pre> -template <class Clock, class Duration> -void do_until(const std::chrono::<b>time_point</b><Clock, Duration>& t) -{ - typename Clock::<b>time_point now</b> = Clock::now(); - if (t > now) - { - typedef typename std::common_type - < - Duration, - typename std::chrono::system_clock::<b>duration</b> - >::type CD; - typedef std::chrono::<b>duration</b><double, std::nano> ID; - - CD d = t - now; - ID us = duration_cast<ID>(d); - if (us < d) - ++us; - ... - } -} -</pre></blockquote> - -<p> -I see no rationale to require the client to append <tt>_type</tt> to <em>some</em> -of those declarations. It seems overly burdensome on the author of <tt>do_until</tt>: -</p> - -<blockquote><pre> -template <class Clock, class Duration> -void do_until(const std::chrono::<b>time_point</b><Clock, Duration>& t) -{ - typename Clock::<b>time_point<span style="color:#C80000">_type</span></b> now = Clock::now(); - if (t > now) - { - typedef typename std::common_type - < - Duration, - typename std::chrono::system_clock::<b>duration<span style="color:#C80000">_type</span></b> - >::type CD; - typedef std::chrono::<b>duration</b><double, std::nano> ID; - - CD d = t - now; - ID us = duration_cast<ID>(d); - if (us < d) - ++us; - ... - } -} -</pre></blockquote> - -<p> -Additionally I'm fairly certain that this suggestion hasn't been implemented. -If it had, it would have been discovered that it is incomplete. <tt>time_point</tt> -also has a nested type (purposefully) named <tt>duration</tt>. -</p> -<blockquote><p> -That is, the current proposed wording would put the WP into an inconsistent state. -</p></blockquote> -<p> -In contrast, -the current WP has been implemented and I've received very favorable feedback -from people using this interface in real-world code. -</p> - -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Bill agrees that distinct names should be used for distinct kinds of entities. -</p> -<p> -Walter would prefer not to suffix type names, -especially for such well-understood terms as "duration". -</p> -<p> -Howard reminds us that the proposed resolution is incomplete, per his comment -in the issue. -</p> -<p> -Move to Open. -</p> -</blockquote> - -<p><i>[ -2009-06-07 Howard adds: -]</i></p> - - -<blockquote> -<p> -Not meaning to be argumentative, but we have a decade of positive experience -with the precedent of using the same name for the nested type as an external -class representing an identical concept. -</p> - -<blockquote><pre> -template<class Category, class T, class Distance = ptrdiff_t, - class Pointer = T*, class Reference = T&> -struct <b>iterator</b> -{ - ... -}; - -template <BidirectionalIterator Iter> -class <b>reverse_iterator</b> -{ - ... -}; - -template <ValueType T, Allocator Alloc = allocator<T> > - requires NothrowDestructible<T> -class list -{ -public: - typedef <i>implementation-defined</i> <b>iterator</b>; - ... - typedef reverse_iterator<iterator> <b>reverse_iterator</b>; - ... -}; -</pre></blockquote> - -<p> -I am aware of <em>zero</em> complaints regarding the use of <tt>iterator</tt> -and <tt>reverse_iterator</tt> as nested types of the containers despite these -names also having related meaning at namespace std scope. -</p> - -<p> -Would we really be doing programmers a favor by renaming these nested types? -</p> - -<blockquote><pre> -template <ValueType T, Allocator Alloc = allocator<T> > - requires NothrowDestructible<T> -class list -{ -public: - typedef <i>implementation-defined</i> <b>iterator_type</b>; - ... - typedef reverse_iterator<iterator> <b>reverse_iterator_type</b>; - ... -}; -</pre></blockquote> - -<p> -I submit that such design contributes to needless verbosity which ends up -reducing readability. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD. No concensus for changing the WP. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 20.12 [time]: -</p> - -<blockquote><pre> -... -template <class Clock, class Duration = typename Clock::duration<ins>_type</ins>> class time_point; -... -</pre></blockquote> - -<p> -Change 20.12.3 [time.clock.req]: -</p> - -<blockquote> -<table border="1"> -<caption>Table 45 -- Clock requirements</caption> -<tr> -<th>Expression</th> -<th>Return type</th> -<th>Operational semantics</th> -</tr> -<tr> -<td>...</td> -<td>...</td> -<td>...</td> -</tr> -<tr> -<td><tt>C1::duration<ins>_type</ins></tt></td> -<td><tt>chrono::duration<C1::rep, C1::period></tt></td> -<td>The native <tt>duration</tt> type of the clock.</td> -</tr> -<tr> -<td><tt>C1::time_point<ins>_type</ins></tt></td> -<td><tt>chrono::time_point<C1></tt> or <tt>chrono::time_point<C2, C1::duration<ins>_type</ins><</tt></td> -<td>The native <tt>time_point</tt> type of the clock. Different clocks may share a <tt>time_point<ins>_type</ins></tt> -definition if it is valid to -compare their <tt>time_point<ins>_type</ins></tt>s by -comparing their respective -<tt>duration<ins>_type</ins></tt>s. <tt>C1</tt> and <tt>C2</tt> shall -refer to the same epoch.</td> -</tr> -<tr> -<td>...</td> -<td>...</td> -<td>...</td> -</tr> -<tr> -<td><tt>C1::now()</tt></td> -<td><tt>C1::time_point<ins>_type</ins></tt></td> -<td>Returns a <tt>time_point<ins>_type</ins></tt> object -representing the current point -in time. -</td> -</tr> -</table> -</blockquote> - -<p> -Change 20.12.7.1 [time.clock.system]: -</p> - -<blockquote> -<p> --1- Objects of class <tt>system_clock</tt> represent wall clock time from the system-wide realtime clock. -</p> - -<blockquote><pre> -class system_clock { -public: - typedef <i>see below</i> rep; - typedef ratio<<i>unspecified</i>, <i>unspecified</i>> period; - typedef chrono::duration<rep, period> duration<ins>_type</ins>; - typedef chrono::time_point<system_clock> time_point<ins>_type</ins>; - static const bool is_monotonic = <i>unspecified</i> ; - - static time_point<ins>_type</ins> now(); - - // Map to C API - static time_t to_time_t (const time_point<ins>_type</ins>& t); - static time_point<ins>_type</ins> from_time_t(time_t t); -}; -</pre></blockquote> - -<p> --2- <tt>system_clock::duration<ins>_type</ins>::min() < system_clock::duration<ins>_type</ins>::zero()</tt> shall be <tt>true</tt>. -</p> - -<pre> -time_t to_time_t(const time_point<ins>_type</ins>& t); -</pre> - -<blockquote><p> --3- <i>Returns:</i> A <tt>time_t</tt> object that represents the same -point in time as <tt>t</tt> when both values are truncated to the -coarser of the precisions of <tt>time_t</tt> and <tt>time_point<ins>_type</ins></tt>. -</p></blockquote> - -<pre> -<tt>time_point<ins>_type</ins></tt> from_time_t(time_t t); -</pre> - -<blockquote><p> --4- <i>Returns:</i> A <tt>time_point<ins>_type</ins></tt> object that represents the same point -in time as <tt>t</tt> when both values are truncated to the coarser of the -precisions of <tt>time_t</tt> and <tt>time_point<ins>_type</ins></tt>. -</p></blockquote> -</blockquote> - -<p> -Change X [time.clock.monotonic]: -</p> - -<blockquote><pre> -class monotonic_clock { -public: - typedef <i>unspecified</i> rep; - typedef ratio<<i>unspecified</i> , <i>unspecified</i>> period; - typedef chrono::duration<rep, period> duration<ins>_type</ins>; - typedef chrono::time_point<<i>unspecified</i> , duration<ins>_type</ins>> time_point<ins>_type</ins>; - static const bool is_monotonic = true; - - static time_point<ins>_type</ins> now(); -}; -</pre></blockquote> - -<p> -Change 20.12.7.3 [time.clock.hires]: -</p> - -<blockquote><pre> -class high_resolution_clock { -public: - typedef <i>unspecified</i> rep; - typedef ratio<<i>unspecified</i> , <i>unspecified</i>> period; - typedef chrono::duration<rep, period> duration<ins>_type</ins>; - typedef chrono::time_point<<i>unspecified</i> , duration<ins>_type</ins>> time_point<ins>_type</ins>; - static const bool is_monotonic = true; - - static time_point<ins>_type</ins> now(); -}; -</pre></blockquote> - - - - - - -<hr> -<h3><a name="959"></a>959. Various threading bugs #9</h3> -<p><b>Section:</b> 30.5.1 [thread.condition.condvar] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2009-01-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.condition.condvar">issues</a> in [thread.condition.condvar].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -30.5.1 [thread.condition.condvar]: <tt>condition_variable::wait_for</tt> -is required to compute the absolute time by adding the duration value to -<tt>chrono::monotonic_clock::now()</tt>, but <tt>monotonic_clock</tt> is not required to -exist. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Move to open. Associate with LWG <a href="lwg-defects.html#859">859</a> and any other monotonic-clock -related issues. -</p></blockquote> - -<p><i>[ -2009-08-01 Howard adds: -]</i></p> - - -<blockquote><p> -I believe that <a href="lwg-defects.html#859">859</a> (currently Ready) addresses this issue, and -that this issue should be marked NAD, solved by <a href="lwg-defects.html#859">859</a> (assuming -it moves to WP). -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Leave open, but expect to be fixed by N2969 revision that Detlef is writing. -</p></blockquote> - -<p><i>[ -2009-11-18 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p> -<p> -<tt>condition_variable::wait_for</tt> no longer refers to -<tt>monotonic_clock</tt>, so this issue is moot. -</p> - - - - - -<hr> -<h3><a name="969"></a>969. What happened to Library Issue 475?</h3> -<p><b>Section:</b> 25.2.4 [alg.foreach] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2009-01-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.foreach">issues</a> in [alg.foreach].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Library Issue <a href="lwg-defects.html#475">475</a> has CD1 status, but the non-normative note in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2723.pdf">N2723</a> -was removed in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2798.pdf">N2798</a> -(25.2.4 [alg.foreach] in both drafts). -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Restore the non-normative note. It might need to be expressed in terms of concepts. -</p> - - - - - -<hr> -<h3><a name="971"></a>971. Spurious diagnostic conversion function</h3> -<p><b>Section:</b> 19.5.2.5 [syserr.errcode.nonmembers] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Beman Dawes <b>Opened:</b> 2009-01-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Anthony Williams raised the question in c++std-lib-22987 "why is there -<tt>std::make_error_code(std::errc)</tt>? What purpose does this serve?" -</p> -<p> -The function <tt>make_error_code(errc e)</tt> is not required, since -<tt>make_error_condition(errc e)</tt> is the function that is needed for <tt>errc</tt> -conversions. <tt>make_error_code(errc e)</tt> appears to be a holdover from my -initial confusion over the distinction between POSIX and operating -systems that conform to the POSIX spec. -</p> - -<p><i>[ -Post Summit: -]</i></p> - - -<blockquote><p> -Recommend Review. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -The designer of the facility (Christopher Kohlhoff) -strongly disagrees that there is an issue here, -and especially disagrees with the proposed resolution. -Bill would prefer to be conservative and not apply this proposed resolution. -Move to Open, and recommend strong consideration for NAD status. -</p></blockquote> - -<p><i>[ -2009-05-21 Beman adds: -]</i></p> - - -<blockquote><p> -My mistake. Christopher and Bill are correct and the issue should be -NAD. The function is needed by users. -</p></blockquote> - -<p><i>[ -2009-07-21 Christopher Kohlhoff adds rationale for <tt>make_error_code</tt>: -]</i></p> - - -<blockquote> -<p> -Users (and indeed library implementers) may need to use the -<tt>errc</tt> codes in portable code. For example: -</p> - -<blockquote><pre> -void do_foo(error_code& ec) -{ -#if defined(_WIN32) - // Windows implementation ... -#elif defined(linux) - // Linux implementation ... -#else - // do_foo not supported on this platform - ec = make_error_code(errc::not_supported); -#endif -} -</pre></blockquote> -</blockquote> - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote><p> -Moved to NAD. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change System error support 19.5 [syserr], Header <tt><system_error></tt> -synopsis, as indicated: -</p> - -<blockquote><pre> -<del>error_code make_error_code(errc e);</del> -error_condition make_error_condition(errc e); -</pre></blockquote> - -<p> -Delete from Class error_code non-member functions -19.5.2.5 [syserr.errcode.nonmembers]: -</p> - -<blockquote><pre> -<del>error_code make_error_code(errc e);</del> -</pre> -<blockquote><p> -<del><i>Returns:</i> <tt>error_code(static_cast<int>(e), -generic_category)</tt>.</del> -</p></blockquote> -</blockquote> - - - - - - -<hr> -<h3><a name="972"></a>972. The term "Assignable" undefined but still in use</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Niels Dekker <b>Opened:</b> 2009-01-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Previous versions of the Draft had a table, defining the Assignable -requirement. For example -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2006/n2134.pdf">N2134</a> -Table 79, "Assignable requirements". But I guess the term "Assignable" -is outdated by now, because the current Committee Draft provides -<tt>MoveAssignable</tt>, <tt>CopyAssignable</tt>, and <tt>TriviallyCopyAssignable</tt> concepts -instead. And as far as I can see, it no longer has a definition of -<tt>Assignable</tt>. (Please correct me if I'm wrong.) Still the word -"Assignable" is used in eight places in the Draft, -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2800.pdf">N2800</a>. -</p> - -<p> -Are all of those instances of "<tt>Assignable</tt>" to be replaced by "<tt>CopyAssignable</tt>"? -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - -<p> -Change Exception Propagation 18.8.5 [propagation]: -</p> -<blockquote><p> -<tt>exception_ptr</tt> shall be <tt>DefaultConstructible</tt>, <tt>CopyConstructible</tt>, -<tt><ins>Copy</ins>Assignable</tt> and <tt>EqualityComparable</tt>. -</p></blockquote> - -<p> -Change Class template reference_wrapper 20.9.4 [refwrap]: -</p> -<blockquote><p> -<tt>reference_wrapper<T></tt> is a <tt>CopyConstructible</tt> and <tt><ins>Copy</ins>Assignable</tt> -wrapper around a reference to an object of type <tt>T</tt>. -</p></blockquote> -<p> -Change Placeholders 20.9.10.4 [func.bind.place]: -</p> -<blockquote><p> -It is implementation defined whether placeholder types are <tt><ins>Copy</ins>Assignable</tt>. -<tt><ins>Copy</ins>Assignable</tt> placeholders' copy assignment operators shall not throw exceptions. -</p></blockquote> -<p> -Change Class template shared_ptr 20.8.2.2 [util.smartptr.shared]: -</p> -<blockquote><p> -Specializations of <tt>shared_ptr</tt> shall be <tt>CopyConstructible</tt>, <tt><ins>Copy</ins>Assignable</tt>, and <tt>LessThanComparable</tt>... -</p></blockquote> -<p> -Change Class template weak_ptr 20.8.2.3 [util.smartptr.weak]: -</p> -<blockquote><p> -Specializations of <tt>weak_ptr</tt> shall be <tt>CopyConstructible</tt>, <tt><ins>Copy</ins>Assignable</tt>, and <tt>LessThanComparable</tt>... -</p></blockquote> -<p> -Change traits typedefs 21.2.2 [char.traits.typedefs] (note: including deletion of reference to 23.1!): -</p> -<blockquote><p> -<i>Requires:</i> <tt>state_type</tt> shall meet the requirements of <tt><ins>Copy</ins>Assignable</tt><del> -(23.1)</del>, <tt>CopyConstructible</tt> (20.1.8), and <tt>DefaultConstructible</tt> types. -</p></blockquote> -<p> -Change Class seed_seq 26.5.7.1 [rand.util.seedseq] (note again: including deletion of reference to 23.1!): -</p> -<blockquote><p> -In addition to the requirements set forth below, instances of -<tt>seed_seq</tt> shall meet the requirements of <tt>CopyConstructible</tt> (20.1.8) and of <tt><ins>Copy</ins>Assignable</tt><del> (23.1)</del>. -</p></blockquote> - -<p> -Note: The proposed resolution of this issue does not deal with the -instance of the term "Assignable" in X [auto.ptr], as this is dealt -with more specifically by LWG <a href="lwg-closed.html#973">973</a>, "<tt>auto_ptr</tt> characteristics", submitted -by Maarten Hilferink. -</p> - - - - - - -<hr> -<h3><a name="973"></a>973. auto_ptr characteristics</h3> -<p><b>Section:</b> X [auto.ptr] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Maarten Hilferink <b>Opened:</b> 2009-01-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#auto.ptr">issues</a> in [auto.ptr].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I think that the Note of X [auto.ptr], paragraph 3 needs a rewrite -since "Assignable" is no longer defined as a concept. -The relationship of <tt>auto_ptr</tt> with the new <tt>CopyAssignable</tt>, <tt>MoveAssignable</tt>, - and <tt>MoveConstructible</tt> concepts should be clarified. -Furthermore, since the use of <tt>auto_ptr</tt> is depreciated anyway, - we can also omit a description of its intended use. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the intent of the proposed resolution. -Move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change X [auto.ptr], paragraph 3: -</p> - -<blockquote><p> -The <tt>auto_ptr</tt> provides a semantics of strict ownership. An -<tt>auto_ptr</tt> owns the ob ject it holds a pointer to. Copying an -<tt>auto_ptr</tt> copies the pointer and transfers ownership to the -destination. If more than one <tt>auto_ptr</tt> owns the same ob ject at -the same time the behavior of the program is undefined. [<i>Note:</i> -The uses of <tt>auto_ptr</tt> include providing temporary -exception-safety for dynamically allocated memory, passing ownership of -dynamically allocated memory to a function, and returning dynamically -allocated memory from a function. -<del><tt>auto_ptr</tt> does not meet the -<tt>CopyConstructible</tt> and <tt>Assignable</tt> requirements for -standard library container elements and thus instantiating a standard -library container with an <tt>auto_ptr</tt> results in undefined -behavior.</del> -<p/> -<ins>Instances of <tt>auto_ptr</tt> shall -meet the <tt>MoveConstructible</tt> and <tt>MoveAssignable</tt> -requirements, but do not meet the <tt>CopyConstructible</tt> and -<tt>CopyAssignable</tt> requirements.</ins> --- <i>end note</i>] -</p></blockquote> - - - - - -<hr> -<h3><a name="977"></a>977. insert iterators inefficient for expensive to move types</h3> -<p><b>Section:</b> 24.5.2 [insert.iterators] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-02-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#insert.iterators">issues</a> in [insert.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The new concepts for the insert iterators mandate an extra copy when -inserting an lvalue: -</p> - -<blockquote><pre> -requires CopyConstructible<Cont::value_type> - back_insert_iterator<Cont>& - operator=(const Cont::value_type& value); -</pre> -<blockquote><p> --1- <i>Effects:</i> <tt>push_back(*container, <b>Cont::value_type(</b>value<b>)</b>);</tt> -</p></blockquote> -</blockquote> - -<p> -The reason is to convert <tt>value</tt> into an rvalue because the current -<tt>BackInsertionContainer</tt> concept only handles <tt>push_back</tt>-ing -rvalues: -</p> - -<blockquote><pre> -concept BackInsertionContainer<typename C> : Container<C> { - void push_back(C&, value_type&&); -} -</pre></blockquote> - -<p> -Without the conversion of <tt>value</tt> to an rvalue, the assignment operator -fails to concept check. -</p> - -<p> -A solution is to modify the <tt>BackInsertionContainer</tt> concept so that -the client can pass in the parameter type for <tt>push_back</tt> similar to -what is already done for the <tt>OutputIterator</tt> concept: -</p> - -<blockquote><pre> -concept BackInsertionContainer<typename C, typename Value = C::value_type&&> - : Container<C> { - void push_back(C&, Value); -} -</pre></blockquote> - -<p> -This allows the assignment operator to be adjusted appropriately: -</p> - -<blockquote><pre> -requires BackInsertionContainer<Cont, Cont::value_type const&> && - CopyConstructible<Cont::value_type> - back_insert_iterator<Cont>& - operator=(const Cont::value_type& value); -</pre> -<blockquote><p> --1- <i>Effects:</i> <tt>push_back(*container, value);</tt> -</p></blockquote> -</blockquote> - -<p><i>[ -We may want to propagate this fix to other concepts such as <tt>StackLikeContainer</tt>. -]</i></p> - - -<p><i>[ -Solution and wording collaborated on by Doug and Howard. -]</i></p> - - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Howard notes that "these operations behaved efficiently until concepts were added." -</p> -<p> -Alisdair is uncertain that the proposed resolution is syntactically correct. -</p> -<p> -Move to Open, and recommend the issue be deferred until after the next -Committee Draft is issued. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -NAD, solved by the removal of concepts. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change [container.concepts.free]: -</p> - -<blockquote> -<pre> -concept FrontInsertionContainer<typename C<ins>, typename Value = C::value_type&&</ins>> - : Container<C> { - void push_front(C&, <del>value_type&&</del> <ins>Value</ins>); - - axiom FrontInsertion(C c, <del>value_type</del> <ins>Value</ins> x) { - x == (push_front(c, x), front(c)); - } -} -</pre> - -<p>...</p> - -<pre> -concept BackInsertionContainer<typename C<ins>, typename Value = C::value_type&&</ins>> - : Container<C> { - void push_back(C&, <del>value_type&&</del> <ins>Value</ins>); -} -</pre> - -<p>...</p> - -<pre> -concept InsertionContainer<typename C<ins>, typename Value = C::value_type&&</ins>> - : Container<C> { - iterator insert(C&, const_iterator, <del>value_type&&</del> <ins>Value</ins>); - - axiom Insertion(C c, const_iterator position, <del>value_type</del> <ins>Value</ins> v) { - v == *insert(c, position, v); - } -} -</pre> - -</blockquote> - -<p> -Change [container.concepts.member]: -</p> - -<blockquote> -<pre> -auto concept MemberFrontInsertionContainer<typename C<ins>, typename Value = C::value_type&&</ins>> - : MemberContainer<C> { - void C::push_front(<del>value_type&&</del> <ins>Value</ins>); - - axiom MemberFrontInsertion(C c, <del>value_type</del> <ins>Value</ins> x) { - x == (c.push_front(x), c.front()); - } -} -</pre> - -<p>...</p> - -<pre> -auto concept MemberBackInsertionContainer<typename C<ins>, typename Value = C::value_type&&</ins>> - : MemberContainer<C> { - void C::push_back(<del>value_type&&</del> <ins>Value</ins>); -} -</pre> - -<p>...</p> - -<pre> -auto concept MemberInsertionContainer<typename C<ins>, typename Value = C::value_type&&</ins>> - : MemberContainer<C> { - iterator C::insert(const_iterator, <del>value_type&&</del> <ins>Value</ins>); - - axiom MemberInsertion(C c, const_iterator position, <del>value_type</del> <ins>Value</ins> v) { - v == *c.insert(position, v); - } -} -</pre> -</blockquote> - -<p> -Change [container.concepts.maps]: -</p> - -<blockquote> -<pre> -template <MemberFrontInsertionContainer C<ins>, typename Value = C::value_type&&</ins>> -concept_map FrontInsertionContainer<C<ins>, Value</ins>> { - typedef Container<C>::value_type value_type; - - void push_front(C& c, <del>value_type&&</del> <ins>Value</ins> v) { c.push_front(static_cast<<del>value_type&&</del> <ins>Value</ins>>(v)); } -} -</pre> - -<p>...</p> - -<pre> -template <MemberBackInsertionContainer C<ins>, typename Value = C::value_type&&</ins>> -concept_map BackInsertionContainer<C<ins>, Value</ins>> { - typedef Container<C>::value_type value_type; - - void push_back(C& c, <del>value_type&&</del> <ins>Value</ins> v) { c.push_back(static_cast<<del>value_type&&</del> <ins>Value</ins>>(v)); } -} -</pre> - -<p>...</p> - -<pre> -template <MemberInsertionContainer C<ins>, typename Value = C::value_type&&</ins>> -concept_map InsertionContainer<C<ins>, Value</ins>> { - typedef Container<C>::value_type value_type; - Container<C>::iterator insert(C& c, Container<C>::const_iterator i, <del>value_type&&</del> <ins>Value</ins> v) - { return c.insert(i, static_cast<<del>value_type&&</del> <ins>Value</ins>>(v)); } -} -</pre> - -</blockquote> - -<p> -Change 24.5.2.1 [back.insert.iterator]: -</p> - -<blockquote><pre> -template <BackInsertionContainer Cont> -class back_insert_iterator { - ... - requires <ins>BackInsertionContainer<Cont, const Cont::value_type&></ins> - <del>CopyConstructible<Cont::value_type></del> - back_insert_iterator<Cont>& - operator=(const Cont::value_type& value); - ... -</pre></blockquote> - -<p> -Change 24.5.2.2.2 [back.insert.iter.op=]: -</p> - -<blockquote> -<pre> -requires <ins>BackInsertionContainer<Cont, const Cont::value_type&></ins> - <del>CopyConstructible<Cont::value_type></del> - back_insert_iterator<Cont>& - operator=(const Cont::value_type& value); -</pre> -<blockquote><p> --1- <i>Effects:</i> <tt>push_back(*container, <del>Cont::value_type(</del>value<del>)</del>);</tt> -</p></blockquote> -</blockquote> - -<p> -Change 24.5.2.3 [front.insert.iterator]: -</p> - -<blockquote><pre> -template <FrontInsertionContainer Cont> -class front_insert_iterator { - ... - requires <ins>FrontInsertionContainer<Cont, const Cont::value_type&></ins> - <del>CopyConstructible<Cont::value_type></del> - front_insert_iterator<Cont>& - operator=(const Cont::value_type& value); - ... -</pre></blockquote> - -<p> -Change 24.5.2.4.2 [front.insert.iter.op=]: -</p> - -<blockquote> -<pre> -requires <ins>FrontInsertionContainer<Cont, const Cont::value_type&></ins> - <del>CopyConstructible<Cont::value_type></del> - front_insert_iterator<Cont>& - operator=(const Cont::value_type& value); -</pre> -<blockquote><p> --1- <i>Effects:</i> <tt>push_front(*container, <del>Cont::value_type(</del>value<del>)</del>);</tt> -</p></blockquote> -</blockquote> - -<p> -Change 24.5.2.5 [insert.iterator]: -</p> - -<blockquote><pre> -template <InsertionContainer Cont> -class insert_iterator { - ... - requires <ins>InsertionContainer<Cont, const Cont::value_type&></ins> - <del>CopyConstructible<Cont::value_type></del> - insert_iterator<Cont>& - operator=(const Cont::value_type& value); - ... -</pre></blockquote> - -<p> -Change 24.5.2.6.2 [insert.iter.op=]: -</p> - -<blockquote> -<pre> -requires <ins>InsertionContainer<Cont, const Cont::value_type&></ins> - <del>CopyConstructible<Cont::value_type></del> - insert_iterator<Cont>& - operator=(const Cont::value_type& value); -</pre> -<blockquote> -<p> --1- <i>Effects:</i> -</p> -<blockquote><pre> -iter = insert(*container, iter, <del>Cont::value_type(</del>value<del>)</del>); -++iter; -</pre></blockquote> -</blockquote> -</blockquote> - - - - - - -<hr> -<h3><a name="979"></a>979. Bad example</h3> -<p><b>Section:</b> 24.5.3 [move.iterators] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-02-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#move.iterators">issues</a> in [move.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -24.5.3 [move.iterators] has an incorrect example: -</p> - -<blockquote> -<p> --2- [<i>Example:</i> -</p> - -<blockquote><pre> -set<string> s; -// populate the set s -vector<string> v1(s.begin(), s.end()); // copies strings into v1 -vector<string> v2(make_move_iterator(s.begin()), - make_move_iterator(s.end())); // moves strings into v2 -</pre></blockquote> - -<p> -<i>-- end example</i>] -</p> -</blockquote> - -<p> -One can not move from a <tt>set</tt> because the iterators return <tt>const</tt> -references. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the proposed resolution. Move to NAD Editorial. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 24.5.3 [move.iterators]/2: -</p> - -<blockquote> -<p> --2- [<i>Example:</i> -</p> - -<blockquote><pre> -<del>set</del><ins>list</ins><string> s; -// populate the <del>set</del><ins>list</ins> s -vector<string> v1(s.begin(), s.end()); // copies strings into v1 -vector<string> v2(make_move_iterator(s.begin()), - make_move_iterator(s.end())); // moves strings into v2 -</pre></blockquote> - -<p> -<i>-- end example</i>] -</p> -</blockquote> - - - - - -<hr> -<h3><a name="980"></a>980. <tt>mutex lock()</tt> missing error conditions</h3> -<p><b>Section:</b> 30.4.1 [thread.mutex.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Ion Gaztañaga <b>Opened:</b> 2009-02-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#thread.mutex.requirements">active issues</a> in [thread.mutex.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.mutex.requirements">issues</a> in [thread.mutex.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -POSIX 2008 adds two return values for <tt>pthread_mutex_xxxlock()</tt>: -<tt>EOWNERDEAD</tt> (<tt>owner_dead</tt>) and <tt>ENOTRECOVERABLE</tt> -(<tt>state_not_recoverable</tt>). In the first case the mutex is locked, -in the second case the mutex is not locked. -</p> - -<p> -Throwing an exception in the first case can be incompatible with the use -of Locks, since the <tt>Lock::owns_lock()</tt> will be <tt>false</tt> when the lock is -being destroyed. -</p> - -<p> -Consider: -</p> - -<blockquote><pre> -//Suppose mutex.lock() throws "owner_dead" -unique_lock ul(&mutex); -//mutex left locked if "owner_dead" is thrown -</pre></blockquote> - -<p> -Throwing an exception with <tt>owner_dead</tt> might be also undesirable if -robust-mutex support is added to C++ and the user has the equivalent of -<tt>pthread_mutex_consistent()</tt> to notify the user has fixed the corrupted -data and the mutex state should be marked consistent. -</p> - -<ol> -<li> -For <tt>state_not_recoverable</tt> add it to the list of Error conditions: -</li> -<li> -For <tt>owner_dead</tt>, no proposed resolution. -</li> -</ol> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Not a defect. Handling these error conditions is an implementation -detail and must be handled below the C++ interface. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - -<p> -Add to 30.4.1 [thread.mutex.requirements], p12: -</p> - -<blockquote> -<p> --12- <i>Error conditions:</i> -</p> - -<ul> -<li> -<tt>operation_not_permitted</tt> -- if the thread does not have the necessary permission to change -the state of the mutex. -</li> -<li> -<tt>resource_deadlock_would_occur</tt> -- if the current thread already owns the mutex and is able -to detect it. -</li> -<li> -<tt>device_or_resource_busy</tt> -- if the mutex is already locked and blocking is not possible. -</li> -<li> -<ins><tt>state_not_recoverable</tt> -- if the state protected by the mutex is not recoverable.</ins> -</li> -</ul> -</blockquote> - - - - - -<hr> -<h3><a name="988"></a>988. <tt>Reflexivity</tt> meaningless?</h3> -<p><b>Section:</b> X [concept.comparison] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-02-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#concept.comparison">issues</a> in [concept.comparison].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -X [concept.comparison] p2: -</p> -<p> -Due to the subtle meaning of <tt>==</tt> inside axioms, the <tt>Reflexivity</tt> axiom does -not do anything as written. It merely states that a value is substitutable -with itself, rather than asserting a property of the <tt>==</tt> operator. -</p> - -<p><b> -Original proposed resolution: -</b></p> - -<p> -Change the definition of <tt>Reflexivity</tt> in X [concept.comparison]: -</p> - -<blockquote><pre> -axiom Reflexivity(T a) { <ins>(</ins>a == a<ins>) == true</ins>; } -</pre></blockquote> - -<p><i>[ -Post Summit: -]</i></p> - - -<blockquote> -<p> -Alisdair: I was wrong. -</p> -<p> -Recommend NAD. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -NAD. -</p> - - - - - -<hr> -<h3><a name="989"></a>989. late_check and library</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-02-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The example in 6.9p2 shows how late_check blocks inhibit concept_map lookup -inside a constrained context, and so inhibit concept map adaption by users -to meet template requirements. -</p> -<p> -Do we need some text in clause 17 prohibitting use of late_check in library -template definitions unless otherwise documented? -</p> - -<p><i>[ -Doug adds: -]</i></p> - - -<blockquote><p> -We need something like this, but it should be a more general statement -about implementations respecting the concept maps provided by the -user. Use of late_check is one way in which implementations can -subvert the concept maps provided by the user, but there are other -ways as well ("pattern-based" overloading, tricks with "auto" concept -maps and defaulted associated type arguments). -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - - -<blockquote><p> -Move to Open, pending proposed wording from Alisdair and/or Doug for further review. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="992"></a>992. Allow implementations to implement C library in the global namespace</h3> -<p><b>Section:</b> 17.6.1.1 [contents] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> P.J. Plauger <b>Opened:</b> 2009-03-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#contents">issues</a> in [contents].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses UK-169 [CD1]</b></p> -<p> -This phrasing contradicts later freedom to implement the C standard -library portions in the global namespace as well as std. (17.6.2.3p4) -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -The proposed wording seems to go too far. -Move back to Open. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote> -<p> -Howard to add NB reference to the description of this issue. -</p> -<p> -Move to NAD. This comment is informative and not normative by the use of -the word "are" instead of the word "shall." -</p> -<p> -A note linking to Annex D would help clarify the intention, here. -</p> -<p> -Robert to Open a separate issue proposing that the standard C headers be -undeprecated, for the purpose of clarifying the standard. -</p> -</blockquote> - -<p><i>[ -2009-07-22 Bill modified the proposed wording with a clarifying footnote. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -Add a footnote to 17.6.1.1 [contents], p2: -</p> - -<blockquote> -<p> --2- All library entities except macros, <tt>operator new</tt> and <tt>operator -delete</tt> are defined within the namespace <tt>std</tt> or namespaces -nested within namespace <tt>std</tt><ins><sup>*</sup></ins>. -</p> - -<p><ins> -<sup>*</sup>The C standard library headers D.5 [depr.c.headers] also define -names within the global namespace, while the C++ headers for -C library facilities 17.6.1.2 [headers] may also define names within -the global namespace. -</ins></p> -</blockquote> - - - - - - -<hr> -<h3><a name="995"></a>995. Operational Semantics Unclear</h3> -<p><b>Section:</b> 17.5.1.3 [structure.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2009-03-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -As a practical matter there's disagreement on the meaning of <i>operational -semantics</i>. If the text in 17.5.1.3 [structure.requirements]p4 isn't -clear, it should be clarified. However, it's not clear whether the -disagreement is merely due to people not being aware of the text. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Agree with the recommended NAD resolution. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Recommend NAD. The text in 17.5.1.3 [structure.requirements] is -perfectly clear. -</p> - - - - - -<hr> -<h3><a name="996"></a>996. Move operation not well specified</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2009-03-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -There are lots of places in the standard where we talk about "the move -constructor" but where we mean "the move operation," i.e. <tt>T( move( x ) )</tt>. -</p> -<p> -We also don't account for whether that operation modifies <tt>x</tt> or not, and -we need to. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to Open, pending proposed wording from Dave for further -review. -</p></blockquote> - - - -<p><i>[ -2010 Rapperswil: -]</i></p> - - -<blockquote><p> -Move to NAD. We define what we expect from a moved-from object in Table 34 [movesconstructible]. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="1000"></a>1000. adjacent_find is over-constrained</h3> -<p><b>Section:</b> 25.2.8 [alg.adjacent.find] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Chris Jefferson <b>Opened:</b> 2009-03-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.adjacent.find">issues</a> in [alg.adjacent.find].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -<b>Addresses UK 296</b> -</p> - -<p> -<tt>adjacent_find</tt> in C++03 allows an arbitrary predicate, but in C++0x -<tt>EqualityComparable/EquivalenceRelation</tt> is required. This forbids a -number of use cases, including: -</p> -<blockquote> -<table> -<tr> -<td valign="top"> -<tt>adjacent_find(begin, end, less<double>)</tt> -</td> -<td> -Find the first -place where a range is not ordered in decreasing order - in use to check -for sorted ranges. -</td> -</tr> -<tr> -<td valign="top"> -<tt>adjacent_find(begin, end, DistanceBiggerThan(6) ) )</tt> -</td> -<td> -Find the first -place in a range where values differ by more than a given value - in use -to check an algorithm which produces points in space does not generate -points too far apart. -</td> -</tr> -</table> -</blockquote> - -<p> -A number of books use predicate which are not equivalence relations in -examples, including "Thinking in C++" and "C++ Primer". -</p> - -<p> -Adding the requirement that the predicate is an <tt>EquivalenceRelation</tt> -does not appear to open up any possibility for a more optimised algorithm. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change the definition of adjacent_find in the synopsis of 25 [algorithms] -and 25.2.8 [alg.adjacent.find] to: -</p> - -<blockquote><pre> -template<ForwardIterator Iter> - requires <del>EqualityComparable</del><ins>HasEqualTo</ins><Iter::value_type<ins>, Iter::value_type</ins>> - Iter adjacent_find(Iter first, Iter last); - -template<ForwardIterator Iter, <del>EquivalenceRelation</del><ins>Predicate</ins><auto, Iter::value_type<ins>, Iter::value_type</ins>> Pred> - requires CopyConstructible<Pred> - Iter adjacent_find(Iter first, Iter last, Pred pred); -</pre></blockquote> - - - - - -<hr> -<h3><a name="1001"></a>1001. Pointers, concepts and headers</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 78</b></p> - -<p> -Related to <a href="lwg-closed.html#1063">1063</a>. -</p> - -<p> -This is effectively an extension of LWG issue <a href="lwg-defects.html#343">343</a>. -</p> -<p> -We know there is an increasing trend (encouraged by conformance testers and -some users) that each library header should supply no more than required to -satisfy the synopsis in the standard. This is typically achieved by -breaking larger headers into smaller subsets, and judicious use of forward -declarations. -</p> -<p> -If we apply this policy to C++0x (per -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2800.pdf">N2800</a>) -it will be very surprising for -people using library algorithms over ranges defined by pointers that they -must <tt>#include <iterator_concepts></tt> for their code to compile again. That is -because pointers do not satisfy any of the iterator concepts without the -<tt>concept_map</tt> supplied in this header. -</p> -<p> -Therefore, I suggest we should require all library headers that make use of -iterator concepts are specifically required to <tt>#include <iterator_concepts></tt>. -</p> -<p> -At a minimum, the list of headers would be: (assuming all are constrained by -concepts) -</p> -<blockquote><pre> -algorithm -array -deque -forward_list -initializer_list -iterator -locale -list -map -memory // if <a href="lwg-closed.html#1029">1029</a> is adopted -memory_concepts -numeric -random -regex -set -string -tuple -unordered_map -unordered_set -utility -vector -</pre></blockquote> - -<p><i>[ -Ganesh adds: -]</i></p> - - -<blockquote> -<p> -The same problems exists for <tt><memory_concepts></tt> and -<tt><container_concepts></tt>. -</p> -<p> -In order to compile <tt><vector></tt> you just need the -definitions of the concepts in <tt><memory_concepts></tt>, the -concept maps defined there are not necessary. Yet, from the user point -of view, if the concept map template for <tt>AllocatableElement</tt> are -not in scope, <tt><vector></tt> is pretty useless. Same for -<tt><tuple></tt> and <tt>ConstructibleWithAllocator</tt>. -</p> -<p> -Similarly, <tt><queue></tt> is not very useful if the concept map -template for <tt>QueueLikeContainer</tt> is not in scope, although the -definition of concept alone is theoretically sufficient. -</p> -<p> -There's a pattern here: if a concept has concept maps "attached", they -should never be separated. -</p> -</blockquote> - -<p><i>[ -Beman provided the proposed resolution for the May 2009 mailing. He -comments: -]</i></p> - - -<blockquote> - -<p>Initially I tried to specify exactly what header should include what other -headers. This was verbose, error prone, hard to maintain, and appeared to add -little value compared to just stating the general rule.</p> - -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Pete believes the proposed wording overconstrains implementers. -Instead of specifying the mechanism, -he prefers a solution that spells out what needs to be declared, -rather than how those declarations are to be provided, -e.g., -</p> -<blockquote><p> -A C++ header shall provide the names -that are required to be defined in that header. -</p></blockquote> -<p> -Bill suggests approaching the wording from a programmer's perspective. -We may want to consider promising that certain widely-used headers -(e.g., the concept headers) are included when needed by other headers. -He feels, however, there is nothing broken now, -although we may want to consider "something nicer." -</p> -<p> -Move to Open status. -</p> - -</blockquote> - -<p><i>[ -2009-06-16 Beman updated the proposed resolution: -]</i></p> - - -<blockquote> - <ul> - <li>The mechanism is no longer specified, as requested in Batavia.</li> - <li>The footnote has been removed since it specified mechanism and also did - not reflect existing practice.</li> - <li>A sentence was added that makes it clear that the existing practice is - permitted.</li> - </ul> -</blockquote> - -<p><i>[ -2009-07-15 Beman updated the proposed resolution: -]</i></p> - - -<p><i>[ -2009-07-17 Beman updated the proposed resolution based on feedback from the LWG in Frankfurt: -]</i></p> - - -<blockquote> -<ul> -<li>Strike two pieces of text considered unnecessary.</li> -<li>Change "definitions" to "declarations and definitions" in two places.</li> -<li>Wording tightened slightly.</li> -</ul> -</blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote> -<p> -Revised Proposed Resolution: -</p> -<p> -A C++ header may include other C++ headers. A C++ header shall provide -the declarations and definitions that appear in its synopsis (3.2 -[basic.def.odr]). A C++ header shown in its synopsis as including other -C++ headers shall provide the declarations and definitions that appear -in the synopses of those other headers. -</p> -<p> -Alisdair: Does this address the BSI comment? -<p/> -Beman: There were several overlapping comments. I tried to handle them -all with one resolution. -<p/> -Alisdair: I'd prefer to see this closed as NAD and have this resolution -be the subject of some other, new issue. -<p/> -Move to NAD Concepts. Howard to open a new issue (<a href="lwg-defects.html#1178">1178</a>) in Ready state with the -Proposed Resolution above. Beman will write up a discussion for the new -issue. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p><i>Change 17.6.5.2 [res.on.headers], Headers, paragraph 1, as indicated:</i></p> - -<blockquote> - -<p> -A C++ header may include other C++ -headers.<del><sup>[footnote]</sup></del> <ins>A C++ header shall provide -the declarations and definitions that appear in its synopsis -(3.2 [basic.def.odr]). A C++ header shown in its synopsis as including -other C++ headers shall provide the same declarations and definitions as -if those other headers were included.</ins> -</p> - - <p><del><sup>[footnote]</sup> C++ headers must include a C++ header that contains - any needed definition (3.2).</del></p> -</blockquote> - - - - - - -<hr> -<h3><a name="1002"></a>1002. Provide bulk include headers</h3> -<p><b>Section:</b> 17.6.1.2 [headers] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#headers">issues</a> in [headers].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK-170 [CD1]</b></p> - -<p> -One of goals of C++0x is to make language easier to teach and for -'incidental' programmers. The fine-grained headers of the C++ library -are valuable in large scale systems for managing dependencies and -optimising build times, but overcomplicated for simple development and -tutorials. Add additional headers to support the whole library through a -single include statement. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We do not all agree that this is an issue, -but we agree that if it needs solving this is the right way to do it. -Move to Tentatively Ready. -</p></blockquote> - -<p><i>[ -2009-07-06 Beman notes: -]</i></p> - - -<blockquote> -<p> -This issue -adds a header <tt><std></tt>. -</p> -<p> -There is a paper to be looked at, -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2905.pdf">N2905</a> -Aggregation headers, that adds -a header <tt><std-all></tt> that is the same thing except it excludes -deprecated headers. -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2905.pdf">N2905</a> -also proposes a second aggregation header. -</p> -<p> -Seems like this issue should be held in abeyance until the LWG has had -a chance to look at <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2905.pdf">N2905</a>. -</p> -</blockquote> - -<p><i>[ -2009-07-06 Howard: I've pulled this issue back to Review. -]</i></p> - - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -No consensus for change. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Insert a new paragraph in 17.6.1.2 [headers] between p4 and p5 -</p> -<blockquote><p> -An additional header <tt><std></tt> shall have the effect of -supplying the entire standard library. [<i>Note:</i> for example, it -might be implemented as a file with an <tt>#include</tt> statement for each of the -headers listed in tables 13 and 14. <i>-- end note</i>] -</p></blockquote> - - - - - -<hr> -<h3><a name="1003"></a>1003. Require more useful headers for freestanding implementations</h3> -<p><b>Section:</b> 17.6.1.3 [compliance] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#compliance">issues</a> in [compliance].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses JP 23 [CD1]</b></p> - -<p> -There is a freestanding implementation including -<tt><type_traits></tt>, <tt><array></tt>, -<tt><ratio></tt>, lately added to Table 13, C++ library headers. -Programmers think them useful and hope that these headers are also added -to Table 15, C++ headers for freestanding implementations, that shows -the set of headers which a freestanding implementation shall include at -least. -</p> - -<p><b>Original proposed resolution</b></p> - -<p> -Add <tt><type_traits></tt>, <tt><array></tt>, -<tt><ratio></tt> to Table 15. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote> -<p> - The <tt><array></tt> header has far too many dependencies to require for a -free-standing implementation. -</p> -<p> -The <tt><ratio></tt> header would be useful, has no dependencies, but is not -strictly necessary. -</p> -<p> -The <tt><type_traits></tt> header is fundamentally a core language facility with a -library interface, so should be supported. -</p> - -<p> -(it is anticipated the resolution will come via an update to paper -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2814.pdf">N2814</a>) -(see also LWG <a href="lwg-closed.html#833">833</a>) -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Leave in Review status pending a paper on freestanding implementations -by Martin Tasker. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote> -<p> -Move this to NAD. -</p> -<p> -We considered all of the listed headers, and found a compelling case -only for the inclusion of <tt><type_traits></tt> in the list of headers required -of a freestanding implementation. -</p> -<p> -See Martin Tasker's paper -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2932.pdf">Fixing Freestanding</a> -which provides the wording to include <tt><type_traits></tt> into freestanding -implementations. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add <tt><type_traits></tt> to Table 15. -</p> - - - - - -<hr> -<h3><a name="1005"></a>1005. <tt>numeric_limits</tt> partial specializations not concept enabled</h3> -<p><b>Section:</b> 18.3.2.3 [numeric.limits] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses JP 26</b></p> - -<p> -<tt>numeric_limits</tt> [partial specializations] does not use concept. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Alisdair will provide a solution as part of treatment of axioms and LWG <a href="lwg-closed.html#902">902</a>. -</p></blockquote> - -<p><i>[ -Post Summit: -]</i></p> - - -<blockquote><p> -Alisdair recommends NAD as the partial specializations are already -constrained by requirements on the primary template. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -The Working Draft does not in general repeat a primary template's constraints -in any specializations. -Move to NAD. -</p></blockquote> - -<p><i>[ -2009-05-25 Howard adds: -]</i></p> - - -<blockquote><p> -A c++std-lib thread starting at c++std-lib-23880 has cast doubt that NAD is the -correct resolution of this issue. Indeed the discussion also casts doubt that -the current proposed wording is the correct resolution as well. Personally I'm -inclined to reset the status to Open. However I'm reverting the status to -that which it had prior to the Batavia recommendation. I'm setting back to Review. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 18.3.2.3 [numeric.limits]: -</p> - -<blockquote><pre> -template<<del>class</del> <ins>Regular</ins> T> class numeric_limits<const T>; -template<<del>class</del> <ins>Regular</ins> T> class numeric_limits<volatile T>; -template<<del>class</del> <ins>Regular</ins> T> class numeric_limits<const volatile T>; -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1007"></a>1007. <tt>throw_with_nested</tt> not concept enabled</h3> -<p><b>Section:</b> 18.8.6 [except.nested] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#except.nested">active issues</a> in [except.nested].</p> -<p><b>View all other</b> <a href="lwg-index.html#except.nested">issues</a> in [except.nested].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses JP 29</b></p> - -<p> -<tt>throw_with_nested</tt> does not use concept. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Agreed. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - -<p> -Alisdair initially proposed wording in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2619.pdf">N2619</a>. -</p> -<p> -We are awaiting an updated paper based on feedback from the San Francisco -review. -</p> - - - - - -<hr> -<h3><a name="1008"></a>1008. <tt>nested_exception</tt> wording unclear</h3> -<p><b>Section:</b> 18.8.6 [except.nested] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#except.nested">active issues</a> in [except.nested].</p> -<p><b>View all other</b> <a href="lwg-index.html#except.nested">issues</a> in [except.nested].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses JP 31</b></p> - -<p> -It is difficult to understand in which case <tt>nested_exception</tt> is applied. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Alisdair will add an example in an update to -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2619.pdf">N2619</a>. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -It doesn't appear that N2619 really addresses this. Alisdair to propose wording. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: -]</i></p> - - -<blockquote><p> -Mark issue 1008 as NAD, the type is adequately described. -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p> -nested_exception is intended to be inherited from by exception classes -that are to be thrown during the handling of another exception, i.e. -when translating from one exception type to another. nested_exception -allows the originally thrown exception to be easily retained in that -scenario. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1009"></a>1009. <tt>InputIterator</tt> post-increment dangerous</h3> -<p><b>Section:</b> 24.2.2 [iterator.iterators] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iterator.iterators">issues</a> in [iterator.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 251</b></p> - -<p> -The post-increment operator is dangerous for a general InputIterator. -The multi-pass guarantees that make it meaningful are defined as part of -the ForwardIterator refinement. Any change will affect only constrained -templates that have not yet been written, so should not break existing -user iterators which remain free to add these operations. This change -will also affect the generalised OutputIterator, although there is no -percieved need for the post-increment operator in this case either. -</p> - -<p><i>[ -2009-07-28 Alisdair adds: -]</i></p> - - -<blockquote><p> -We still think the issue is relevant, but needs totally rewording in -non-concept language. We would like to see the issue retained as Open, -rather than deferred as NAD Concepts. Review status is no longer -appropriate. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -NAD. Without concepts we do not feel that input iterator post increment -is broken. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 24.2.2 [iterator.iterators]: -</p> - -<blockquote><pre> -concept Iterator<typename X> : Semiregular<X> { - MoveConstructible reference = typename X::reference; - <del>MoveConstructible postincrement_result;</del> - - <del>requires HasDereference<postincrement_result>;</del> - - reference operator*(X&&); - X& operator++(X&); - <del>postincrement_result operator++(X&, int);</del> -} -</pre> - -<p>...</p> -<pre> -<del>postincrement_result operator++(X& r, int);</del> -</pre> - -<blockquote><p> -<del>-3- <i>Effects:</i> equivalent to <tt>{ X tmp = r; ++r; return tmp; }</tt>.</del> -</p></blockquote> - -</blockquote> - -<p> -Change 24.2.3 [input.iterators]: -</p> - -<blockquote> -<pre> -concept InputIterator<typename X> : Iterator<X>, EqualityComparable<X> { - ObjectType value_type = typename X::value_type; - MoveConstructible pointer = typename X::pointer; - - SignedIntegralLike difference_type = typename X::difference_type; - - requires IntegralType<difference_type> - && Convertible<reference, const value_type &>; - && Convertible<pointer, const value_type*>; - - <del>requires Convertible<HasDereference<postincrement_result>::result_type, const value_type&>;</del> - - pointer operator->(const X&); -} -</pre> -</blockquote> - -<p> -Change 24.2.4 [output.iterators]: -</p> - -<blockquote> -<pre> -auto concept OutputIterator<typename X, typename Value> { - requires Iterator<X>; - - typename reference = Iterator<X>::reference; - <del>typename postincrement_result = Iterator<X>::postincrement_result;</del> - requires SameType<reference, Iterator<X>::reference> - <del>&& SameType<postincrement_result, Iterator<X>::postincrement_result></del> - <del>&& Convertible<postincrement_result, const X&></del> - && HasAssign<reference, Value> - <del>&& HasAssign<HasDereference<postincrement_result>::result_type, Value></del>; -} -</pre> -</blockquote> - -<p> -Change 24.2.5 [forward.iterators]: -</p> - -<p><i>[ -See <a href="lwg-closed.html#1084">1084</a> which is attempting to change this same area in a compatible -way. -]</i></p> - - -<blockquote> -<pre> -concept ForwardIterator<typename X> : InputIterator<X>, Regular<X> { - <del>requires Convertible<postincrement_result, const X&>;</del> - - <ins>MoveConstructible postincrement_result;</ins> - <ins>requires HasDereference<postincrement_result> - && Convertible<HasDereference<postincrement_result>::result_type, const value_type&>;</ins> - - <ins>postincrement_result operator++(X&, int);</ins> - - axiom MultiPass(X a, X b) { - if (a == b) *a == *b; - if (a == b) ++a == ++b; - } -} -</pre> - -<blockquote> -<p>-4- ...</p> -</blockquote> - -<pre> -<ins>postincrement_result operator++(X& r, int);</ins> -</pre> - -<blockquote> -<p> -<ins>-5- <i>Effects:</i> equivalent to <tt>{ X tmp = r; ++r; return tmp; }</tt>.</ins> -</p> -</blockquote> - -</blockquote> - - - - - - -<hr> -<h3><a name="1010"></a>1010. <tt>operator-=</tt> should use default in concept</h3> -<p><b>Section:</b> 24.2.7 [random.access.iterators] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#random.access.iterators">issues</a> in [random.access.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 263</b></p> - -<p> -This requirement on <tt>operator-=</tt> would be better expressed as a default -implementation in the concept, with a matching axiom. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -The proposed resolution should also remove -paragraph 5 and the declaration that precedes it. -Further, we should provide an axiom -that captures the desired semantics. -This may be a broader policy to be applied. -Move to Open. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 24.2.7 [random.access.iterators]: -</p> - -<blockquote><pre> -concept RandomAccessIterator<typename X> : BidirectionalIterator<X>, LessThanComparable<X> { - ... - X& operator-=(X& <ins>x</ins>, difference_type <ins>n</ins>)<ins> { return x += -n</ins>;<ins> }</ins> - ... -} -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1013"></a>1013. Remove <tt>IsSameType</tt> hold-over constraints</h3> -<p><b>Section:</b> 25.4.7 [alg.min.max] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.min.max">issues</a> in [alg.min.max].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 305</b></p> - -<p> -The negative requirement on <tt>IsSameType</tt> is a hold-over from an earlier -draught with a variadic template form of <tt>min/max</tt> algorith. It is no -longer necessary. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the proposed resolution. -Move to Tentatively Ready. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -We believe this is NAD, but this needs to be reviewed against the -post-remove-concepts draft. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 25 [algorithms]: -</p> - -<blockquote><pre> -template<class T, StrictWeakOrder<auto, T> Compare> - <del>requires !SameType<T, Compare> && CopyConstructible<Compare></del> - const T& min(const T& a, const T& b, Compare comp); -... -template<class T, StrictWeakOrder<auto, T> Compare> - <del>requires !SameType<T, Compare> && CopyConstructible<Compare></del> - const T& max(const T& a, const T& b, Compare comp); -... -template<class T, StrictWeakOrder<auto, T> Compare> - <del>requires !SameType<T, Compare> && CopyConstructible<Compare></del> - pair<const T&, const T&> minmax(const T& a, const T& b, Compare comp); -</pre></blockquote> - -<p> -Change 25.4.7 [alg.min.max], p1, p9 and p17: -</p> - -<blockquote><pre> -template<class T, StrictWeakOrder<auto, T> Compare> - <del>requires !SameType<T, Compare> && CopyConstructible<Compare></del> - const T& min(const T& a, const T& b, Compare comp); -... -template<class T, StrictWeakOrder<auto, T> Compare> - <del>requires !SameType<T, Compare> && CopyConstructible<Compare></del> - const T& max(const T& a, const T& b, Compare comp); -... -template<class T, StrictWeakOrder<auto, T> Compare> - <del>requires !SameType<T, Compare> && CopyConstructible<Compare></del> - pair<const T&, const T&> minmax(const T& a, const T& b, Compare comp); -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1015"></a>1015. C++ programs - but not users - need to provide support <tt>concept_map</tt>s</h3> -<p><b>Section:</b> X [concept.transform] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#concept.transform">issues</a> in [concept.transform].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 199</b></p> - -<p> -The requirement that programs do not supply <tt>concept_maps</tt> should -probably be users do not supply their own <tt>concept_map</tt> -specializations. The program will almost certainly supply -<tt>concept_maps</tt> - the standard itself supplies a specialization -for <tt>RvalueOf</tt> references. Note that the term <i>program</i> is -defined in 3.5 [basic.link]p1 and makes no account of the -standard library being treated differently to user written code. -</p> - -<p><i>[ -2009-05-09 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -The same problem is present in the words added for the -<tt>LvalueReference/RvalueReference</tt> concepts last meeting. -</p> -<p> -With three subsections requiring the same constraint, I'm wondering if there -is a better way to organise this section. -Possible 20.2.1 -> 20.2.3 belong in the fundamental concepts clause in - [concept.support]? While they can be implemented purely as a -library feature without additional compiler support, they are pretty -fundamental and we want the same restriction on user-concept maps as is -mandated there. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the issue, -but believe the wording needs further improvement. -We want to investigate current definitions for nomenclature such as -"user" and "program." -Move to Open pending the recommended investigation. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change X [concept.transform] p2: -</p> - -<blockquote><p> --2- A <del>program</del> <ins>user</ins> shall not provide concept maps for -any concept in 20.1.1. -</p></blockquote> - -<p> -Change [concept.true] p2: -</p> - -<blockquote><p> --2- <i>Requires:</i> a <del>program</del> <ins>user</ins> shall not -provide a concept map for the <tt>True</tt> concept. -</p></blockquote> - -<p> -Change [concept.classify] p2: -</p> - -<blockquote><p> --2- <i>Requires:</i> a <del>program</del><ins>user</ins> shall not provide concept -maps for any concept in this section. -</p></blockquote> - - - - - - -<hr> -<h3><a name="1016"></a>1016. Provide <tt>LessThanComparable</tt> and <tt>EqualityComparable</tt> for <tt>FloatingPointType</tt></h3> -<p><b>Section:</b> X [concept.comparison] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#concept.comparison">issues</a> in [concept.comparison].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses JP 33</b></p> - -<p> -<tt>LessThanComparable</tt> and <tt>EqualityComparable</tt> don't correspond to NaN. -</p> - -<p><b>Original proposed resolution:</b></p> - -<p> -Apply <tt>concept_map</tt> to these concepts at <tt>FloatingPointType</tt>. -</p> - -<p><i>[ -Post Summit, Alisdair adds: -]</i></p> - - -<blockquote> -<p> -I don't understand the proposed resolution - there is no such thing as a -'negative' concept_map, and these concepts are auto concepts that match -float/double etc. Also not clear how we are supposed to match values to -concepts. -</p> -<p> -Recommend NAD and treat as a subset of issue <a href="lwg-closed.html#902">902</a>. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Recommend NAD. -</p> - - - - - -<hr> -<h3><a name="1017"></a>1017. Floating-point types should not satisfy <tt>Regular</tt></h3> -<p><b>Section:</b> X [concept.regular] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US 66</b></p> - -<p> -Application of the <tt>Regular</tt> concept to floating-point types appears to be -controversial (see long discussion on std-lib reflector). -</p> - -<p><b>Original proposed resolution:</b></p> - -<p> -State that the <tt>Regular</tt> concept does not apply to floating-point types. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote> -<p> -Recommend that we handle the same as JP 33 / <a href="lwg-closed.html#1016">1016</a>. -</p> -</blockquote> - -<p><i>[ -Post Summit, Alisdair adds: -]</i></p> - - -<blockquote> -<p> -Recommend Open, and review after resolution of <a href="lwg-closed.html#902">902</a> and revised axiom -feature. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1018"></a>1018. Trait specifications should be expressed in terms of concepts</h3> -<p><b>Section:</b> 20.10 [meta] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#meta">active issues</a> in [meta].</p> -<p><b>View all other</b> <a href="lwg-index.html#meta">issues</a> in [meta].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US 70 [CD1]</b></p> - -<p> -Specifications now expressed via narrative text are more accurately and -clearly expressed via executable code. -</p> -<p> -Wherever concepts are available that directly match this section's type -traits, express the traits in terms of the concepts instead of via -narrative text. Where the type traits do not quite match the -corresponding concepts, bring the two into alignment so as to avoid two -nearly-identical notions. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote> -<p> -We think that this is a good idea, but it requires a lot of work. If someone -submits a paper proposing specific changes, we would be happy to review it -at the next meeting. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1020"></a>1020. Restore <tt>aligned_union</tt></h3> -<p><b>Section:</b> 20.10.7.6 [meta.trans.other] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#meta.trans.other">active issues</a> in [meta.trans.other].</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.trans.other">issues</a> in [meta.trans.other].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 204 [CD1]</b></p> - -<p> -It is not possible to create a variant union based on a parameter pack -expansion, e.g. to implement a classic discriminated union template. -</p> - -<p><b>Original proposed resolutuion:</b></p> - -<p> -Restore <tt>aligned_union</tt> template that was removed by LWG issue <a href="lwg-defects.html#856">856</a>. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Agree. The need for <tt>aligned_union</tt> is compelling enough to reinstate. -</p></blockquote> - -<p><i>[ -Post Summit, Alisdair adds: -]</i></p> - - -<blockquote><p> -Paper -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2843.html">N2843</a> -proposes an extension to the <tt>[[align]]</tt> attribute -that further diminishes the need for this template. Recommend NAD. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark NAD as suggested. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1022"></a>1022. Pointer-safety API has nothing to do with smart pointers</h3> -<p><b>Section:</b> 20.7.4 [util.dynamic.safety] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#util.dynamic.safety">issues</a> in [util.dynamic.safety].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 212 [CD1]</b></p> - -<p> -The pointer-safety API is nothing to do with smart pointers, so does not -belong in 20.8.2 [util.smartptr]. In fact it is a set of language -support features are really belongs in clause 18 [language.support], -with the contents declared in a header that deals with language-support -of memory management. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Agree in principle, but not with the proposed resolution. We believe it -belongs either a subsection of either 20 [utilities] or -20.7 [memory] as part of the general reorganization of -20 [utilities]. The declaration should stay in <tt><memory></tt>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1023"></a>1023. Unclear inheritance relation for <tt>std::function</tt></h3> -<p><b>Section:</b> 20.9.12.2 [func.wrap.func] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#func.wrap.func">active issues</a> in [func.wrap.func].</p> -<p><b>View all other</b> <a href="lwg-index.html#func.wrap.func">issues</a> in [func.wrap.func].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses DE 22 [CD1]</b></p> - -<p>Related to issue <a href="lwg-defects.html#1114">1114</a>.</p> - -<p> -The conditions for deriving from <tt>std::unary_function</tt> and -<tt>std::binary_function</tt> are unclear: The condition would also be satisfied if -<tt>ArgTypes</tt> were <tt>std::vector<T1></tt>, because it (arguably) -"contains" <tt>T1</tt>. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Agree. <tt>std::reference_wrapper</tt> has the same structure, and we -suggest that <tt>std::function</tt> be presented in the same way as -<tt>std::reference_wrapper</tt>. -</p></blockquote> - -<p><i>[ -2009-05-09 Alisdair adds: -]</i></p> - - -<blockquote><p> -Phrasing should be "publicly and unambiguously derived from" and probably back in -<tt>reference_wrapper</tt> too. Updated wording supplied. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the proposed wording. -Move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -(no changes to <tt><functional></tt> synopsis required) -</p> - -<p> -Change synopsis in Class template function 20.9.12.2 [func.wrap.func]: -</p> - -<blockquote><pre> -template<Returnable R, CopyConstructible... ArgTypes> -class function<R(ArgTypes...)> - : public unary_function<T1, R> // <del><i>iff</i> sizeof...(ArgTypes) == 1 <i>and</i></del> <ins><i>see below</i></ins> - <del>// ArgTypes <i>contains</i> T1</del> - : public binary_function<T1, T2, R> // <del><i>iff</i> sizeof...(ArgTypes) == 2 <i>and</i></del> <ins><i>see below</i></ins> - <del>// ArgTypes <i>contains</i> T1 <i>and</i> T2</del> -{ - ... -</pre></blockquote> - -<p> -Add new p1/p2 before 20.9.12.2.1 [func.wrap.func.con]: -</p> - -<blockquote> -<p><ins> -The template instantiation <tt>function<R(T1)></tt> shall be publicly and -unambiguously derived from -<tt>std::unary_function<T1,R></tt> if and only if the template type parameter -is a function type taking one argument of type <tt>T1</tt> and returning <tt>R</tt>. -</ins></p> - -<p><ins> -The template instantiation <tt>function<R(T1,T2)></tt> shall be publicly and -unambiguously derived from -<tt>std::binary_function<T1,T2,R></tt> if and only if the template type -parameter is a function type taking two arguments of type <tt>T1</tt> and <tt>T2</tt> and -returning <tt>R</tt>. -</ins></p> - -<pre> -explicit function(); -</pre> -</blockquote> - - - - - - -<hr> -<h3><a name="1024"></a>1024. <tt>std::function</tt> constructors overly generous</h3> -<p><b>Section:</b> 20.9.12.2 [func.wrap.func] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#func.wrap.func">active issues</a> in [func.wrap.func].</p> -<p><b>View all other</b> <a href="lwg-index.html#func.wrap.func">issues</a> in [func.wrap.func].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses JP 39 [CD1]</b></p> - -<p> -There are no requires corresponding to <tt>F</tt> of <tt>std::function</tt>. -</p> - -<p><i>[ -2009-05-01 Daniel adds: -]</i></p> - - -<blockquote><p> -<a href="lwg-defects.html#1070">1070</a> removes the second constructor. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the proposed resolution. -Move to Tentatively Ready. -If issue <a href="lwg-defects.html#1070">1070</a> is accepted, -the changes to the second constructor -in this issue are moot. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt: -]</i></p> - - -<blockquote><p> -Constructors have no definition. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Correct as follows in 20.9.12.2 [func.wrap.func] (class definition) -</p> - -<blockquote><pre> - template<class F, Allocator Alloc> - <ins>requires ConstructibleWithAllocator<F, Alloc> - && call=Callable<F, ArgTypes...> - && Convertible<call::result_type, R></ins> - function(allocator_arg_t, const Alloc&, F); - template<class F, Allocator Alloc> - <ins>requires ConstructibleWithAllocator<F,Alloc> - && call=Callable<F, ArgTypes...> - && Convertible<call::result_type, R></ins> - function(allocator_arg_t, const Alloc&, F&&); -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1026"></a>1026. Smart pointers need to be concept-constrained templates</h3> -<p><b>Section:</b> 20.7 [memory] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#memory">issues</a> in [memory].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 209 [CD1]</b></p> - -<p> -Smart pointers cannot be used in constrained templates. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -We look forward to a paper on this topic. We recommend no action until a -paper is available. We understand that a paper is forthcoming. -</p></blockquote> - -<p><i>[ -Peter Dimov adds: -]</i></p> - - -<blockquote><p> -<tt>shared_ptr<T></tt> and <tt>weak_ptr<T></tt> support all -types <tt>T</tt> for which <tt>T*</tt> is valid. In other words, a -possible (partial) resolution is to change class <tt>T</tt> to -<tt>PointeeType T</tt> for <tt>shared_ptr</tt>, <tt>weak_ptr</tt> and -possibly <tt>enable_shared_from_this</tt>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1027"></a>1027. <tt>std::allocator</tt> needs to be a concept-constrained template</h3> -<p><b>Section:</b> 20.7.9 [default.allocator] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#default.allocator">issues</a> in [default.allocator].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 213 [CD1]</b></p> - -<p> -<tt>std::allocator</tt> should be constrained to simplify its use on constrained -contexts. This library component models allocation from free store via the -new operator so choose constraints to -match. The Allocator concept allows for a wider variety of allocators that -users may choose to supply if their allocation model does not require -operator new, without impacting the -requirements of this template. -</p> - -<p> -Suggested direction: -</p> -<p> -The primary allocator template should be constrained to require -<tt>ObjectType<T></tt> and <tt>FreeStoreAllocatable<T></tt>. -Further operations to be constrained as required. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Agree as stated. A future paper will address additional related issues. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1028"></a>1028. <tt>raw_storage_iterator</tt> needs to be a concept-constrained template</h3> -<p><b>Section:</b> 20.7.10 [storage.iterator] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#storage.iterator">issues</a> in [storage.iterator].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 214 [CD1]</b></p> - -<p> -<tt>raw_storage_iterator</tt> needs constraining as an iterator adaptor to be safely -used in constrained templates -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -We look forward to a paper on this topic. We recommend no action until a -paper is available. -</p></blockquote> - -<p><i>[ -Post Summit Alisdair provided wording and rationale. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -20.7 [memory] p2 -</p> -<p> -Update the synopsis for <tt><memory></tt> -</p> -<blockquote><pre> -// 20.7.8, raw storage iterator: -template <<del>class</del> <ins>ForwardIterator</ins> Out<del>put</del>Iter<del>ator</del>, <del>class</del> <ins>ObjectType</ins> T> - <ins>requires OutputIterator< OutIter, T ></ins> - class raw_storage_iterator; - -<ins>template <ForwardIterator OutIter, ObjectType T> - requires OutputIterator< OutIter, T > - concept_map Iterator<raw_storage_iterator< OutIter, T > > { }</ins> -</pre></blockquote> - - -<p> -20.7.10 [storage.iterator] p1 -</p> -<p> -Replace class template definition with: -</p> -<blockquote><pre> -namespace std { - template <<del>class</del> <ins>ForwardIterator</ins> Out<del>put</del>Iter<del>ator</del>, <del>class</del> <ins>ObjectType</ins> T> - <ins>requires OutputIterator< OutIter, T ></ins> - class raw_storage_iterator - : public iterator<output_iterator_tag,void,void,void,void> { - public: - explicit raw_storage_iterator(Out<del>put</del>Iter<del>ator</del> x); - - raw_storage_iterator<del><OutputIterator,T></del>& operator*(); - raw_storage_iterator<del><OutputIterator,T></del>& operator=(const T& element); - raw_storage_iterator<del><OutputIterator,T></del>& operator++(); - raw_storage_iterator<del><OutputIterator,T></del> operator++(int); - }; - - <ins>template <ForwardIterator OutIter, ObjectType T> - requires OutputIterator< OutIter, T > - concept_map Iterator<raw_storage_iterator< OutIter, T > > { }</ins> -} -</pre></blockquote> - - -<p><b>Rationale:</b></p> -<p> -<tt>raw_storage_iterator</tt> has to adapt a <tt>ForwardIterator</tt>, -rather than just an <tt>InputIterator</tt> for two reasons: -</p> - -<ol style="list-style-type:lower-roman"> -<li> -The initial iterator passed by value is expected to remain valid, -pointing to the initialized region of memory. -</li> -<li> -to avoid breaking the declaration of post-increment operator which would -require some kind of proxy formulation to support generalised InputIterators. -</li> -</ol> - - - - - - -<hr> -<h3><a name="1029"></a>1029. Specialized algorithms for memory management need to be concept-constrained templates</h3> -<p><b>Section:</b> 20.7.12 [specialized.algorithms] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#specialized.algorithms">issues</a> in [specialized.algorithms].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 210 [CD1]</b></p> - -<p>Related to <a href="lwg-closed.html#582">582</a></p> - -<p> -Specialized algorithms for memory management need requirements to be -easily usable in constrained templates. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -We look forward to a paper on this topic. We recommend no action until a -paper is available. -</p></blockquote> - -<p><i>[ -Post Summit Alisdair provided wording. -]</i></p> - - -<p><i>[ -Post Summit: -]</i></p> - - -<blockquote> -<p> -Daniel adds: -</p> - -<blockquote> -<ol> -<li> -I suggest <tt>Size</tt> should require <tt>IntegralLike</tt> and not <tt>UnsignedIntegralLike</tt>, -because otherwise simple int-literals could not be provided as arguments -and it would conflict with other algorithms that only require <tt>IntegralLike</tt>. -</li> -<li> -<p> -The current for-loop-test relies on evaluation in boolean context which is -not provided by <tt>ArithmeticLike</tt> and it's refinements. I propose to change the -corresponding for-loop-headers to: -</p> -<ol style="list-style-type:lower-alpha"> -<li> -for <tt>uninitialized_copy_n</tt>: <tt>for ( ; n > Size(0); ++result, ++first, --n) {</tt> -</li> -<li> -for <tt>uninitialized_fill_n</tt>: <tt>for (; n > Size(0); ++first, --n) {</tt> -</li> -</ol> -</li> -</ol> -</blockquote> - -<p> -Alisdair adds: -</p> -<blockquote><p> -For the record I agree with Daniel's suggestion. -</p></blockquote> - -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -20.7 [memory] p2 -</p> -<p> -Update the synopsis for <tt><memory></tt> -</p> -<blockquote><pre> -template <<del>class</del> InputIterator <ins>InIter</ins>, - <del>class ForwardIterator</del> <ins>OutputIterator<auto, InIter::reference> OutIter</ins>> - <ins>requires ForwardIterator<OutIter></ins> - <del>ForwardIterator</del> <ins>OutIter</ins> - uninitialized_copy(<del>InputIterator</del> <ins>InIter</ins> first, <del>InputIterator</del> <ins>InIter</ins> last, - <del>ForwardIterator</del> <ins>OutIter</ins> result); - -template <<del>class</del> InputIterator <ins>InIter</ins>, - <del>class</del> <ins>IntegralLike</ins> Size, - <del>class ForwardIterator</del> <ins>OutputIterator<auto, InIter::reference> OutIter</ins>> - <ins>requires ForwardIterator<OutIter></ins> - <del>ForwardIterator</del> <ins>OutIter</ins> - uninitialized_copy_n(<del>InputIterator</del> <ins>InIter</ins> first, Size n, - <del>ForwardIterator</del> <ins>OutIter</ins> result); - -template <<del>class</del> ForwardIterator <ins>Iter</ins>, <del>class</del> <ins>ObjectType</ins> T> - <ins>requires Constructible< Iter::value_type, const T& ></ins> - void uninitialized_fill(<del>ForwardIterator</del> <ins>Iter</ins> first, <del>ForwardIterator</del> <ins>Iter</ins> last, - const T& x); - -template <<del>class</del> ForwardIterator <ins>Iter</ins>, <del>class</del> <ins>IntegralLike</ins> Size, <del>class</del> <ins>ObjectType</ins> T> - <ins>requires Constructible< Iter::value_type, const T& ></ins> - void - uninitialized_fill_n(<del>ForwardIterator</del> <ins>Iter</ins> first, Size n, const T& x); -</pre></blockquote> - -<p> -Update as follows: -</p> - -<p> -uninitialized_copy 20.7.12.2 [uninitialized.copy] -</p> - -<blockquote><pre> -template <<del>class</del> InputIterator <ins>InIter</ins>, - <del>class ForwardIterator</del> <ins>OutputIterator<auto, InIter::reference> OutIter</ins>> - <ins>requires ForwardIterator<OutIter></ins> - <del>ForwardIterator</del> <ins>OutIter</ins> - uninitialized_copy(<del>InputIterator</del> <ins>InIter</ins> first, <del>InputIterator</del> <ins>InIter</ins> last, - <del>ForwardIterator</del> <ins>OutIter</ins> result); -</pre> - -<blockquote> -<p> --1- <i>Effects:</i> -</p> -<blockquote><pre> -for (; first != last; ++result, ++first) { - new (static_cast<void*>(&*result)) - <del>typename iterator_traits<ForwardIterator></del> <ins>OutIter</ins>::value_type(*first); -} -</pre></blockquote> - -<p> --2- <i>Returns:</i> <tt>result</tt> -</p> - -</blockquote> - -<pre> -template <<del>class</del> InputIterator <ins>InIter</ins>, - <del>class</del> <ins>IntegralLike</ins> Size, - <del>class ForwardIterator</del> <ins>OutputIterator<auto, InIter::reference> OutIter</ins>> - <ins>requires ForwardIterator<OutIter></ins> - <del>ForwardIterator</del> <ins>OutIter</ins> - uninitialized_copy_n(<del>InputIterator</del> <ins>InIter</ins> first, Size n, - <del>ForwardIterator</del> <ins>OutIter</ins> result); -</pre> - -<blockquote> -<p> --3- Effects: -</p> -<blockquote><pre> -for ( ; n > <ins>Size(</ins>0<ins>)</ins>; ++result, ++first, --n) { - new (static_cast<void*>(&*result)) - <del>typename iterator_traits<ForwardIterator></del> <ins>OutIter</ins>::value_type(*first); -} -</pre></blockquote> -<p> --4- <i>Returns:</i> result -</p> -</blockquote> - -</blockquote> - - -<p> -uninitialized_fill 20.7.12.3 [uninitialized.fill] -</p> - -<blockquote><pre> -template <<del>class</del> ForwardIterator <ins>Iter</ins>, <del>class</del> <ins>ObjectType</ins> T> - <ins>requires Constructible< Iter::value_type, const T& ></ins> - void uninitialized_fill(<del>ForwardIterator</del> <ins>Iter</ins> first, <del>ForwardIterator</del> <ins>Iter</ins> last, - const T& x); -</pre> - -<blockquote> -<p> --1- <i>Effects:</i> -</p> -<blockquote><pre> -for (; first != last; ++first) { - new ( static_cast<void*>( &*first) ) - <del>typename iterator_traits<ForwardIterator></del> <ins>Iter</ins>::value_type(x); -} -</pre></blockquote> -</blockquote> -</blockquote> - - -<p> -uninitialized_fill_n 20.7.12.4 [uninitialized.fill.n] -</p> - -<blockquote><pre> -template <<del>class</del> ForwardIterator <ins>Iter</ins>, <del>class</del> <ins>IntegralLike</ins> Size, <del>class</del> <ins>ObjectType</ins> T> - <ins>requires Constructible< Iter::value_type, const T& ></ins> - void - uninitialized_fill_n(<del>ForwardIterator</del> <ins>Iter</ins> first, Size n, const T& x); -</pre> - -<blockquote> -<p> --1- <i>Effects:</i> -</p> -<blockquote><pre> -for (; n<del>--</del> <ins>> Size(0)</ins>; ++first<ins>, --n</ins>) { - new ( static_cast<void*>( &*first) ) - <del>typename iterator_traits<ForwardIterator></del> <ins>Iter</ins>::value_type(x); -} -</pre></blockquote> -</blockquote> -</blockquote> - - - - - - -<hr> -<h3><a name="1032"></a>1032. Tome utility templates need to be concept-constrained</h3> -<p><b>Section:</b> 20.12 [time] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#time">issues</a> in [time].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses JP 45 [CD1]</b></p> - -<p> -<tt>Rep</tt>, <tt>Period</tt>, <tt>Clock</tt> and <tt>Duration</tt> -don't correspond to concept. -</p> -<blockquote><pre> -template <class Rep, class Period = ratio<1>> class duration; -template <class Clock, class Duration = typename Clock::duration> class time_point; -</pre></blockquote> -<p> -Make concept for <tt>Rep</tt>, <tt>Period</tt>, <tt>Clock</tt> and <tt>Duration</tt>. -Fix 20.12 [time] and <tt>wait_until</tt> -and <tt>wait_for</tt>'s template parameter at 30 [thread]. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -We agree that this section needs concepts. We look forward to a paper on -this topic. We recommend no action until a paper is available. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1035"></a>1035. <tt><array>::swap</tt> can invalidate references, pointers, and iterators</h3> -<p><b>Section:</b> 23.2.1 [container.requirements.general] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#container.requirements.general">active issues</a> in [container.requirements.general].</p> -<p><b>View all other</b> <a href="lwg-index.html#container.requirements.general">issues</a> in [container.requirements.general].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 226 [CD1]</b></p> - -<p> -<tt><array></tt> must be added to this list. In particular it -doesn't satisfy: - no <tt>swap()</tt> function invalidates any -references, pointers, or iterators referring to the elements of the -containers being swapped. and probably doesn't satisfy: - no -<tt>swap()</tt> function throws an exception. -</p> -<p> -If <tt><array></tt> remains a container, this will have to also -reference <tt>array</tt>, which will then have to say which of these -points it satisfies. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Agree. The proposed resolution is incomplete. Further work required. -</p></blockquote> - -<p><i>[ -2009-05-01 Daniel adds: -]</i></p> - - -<blockquote><p> -Issue <a href="lwg-closed.html#1099">1099</a> also suggests adding move constructor to this. -</p></blockquote> - -<p><i>[ -2009-07 post-Frankfurt: -]</i></p> - - -<blockquote><p> -Howard is to draft a note that explains what happens to references. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD. No consensus for change. -</p></blockquote> - - - -<p><i>[ -2009-08-01 Howard provided wording. -]</i></p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add a paragraph to 23.3.2.3 [array.special]: -</p> - -<blockquote><pre> -template <Swappable T, size_t N> void swap(array<T,N>& x, array<T,N>& y); -</pre> -<blockquote> -<p> -<i>Effects:</i> -</p> -<blockquote><pre> -swap_ranges(x.begin(), x.end(), y.begin()); -</pre></blockquote> - -<p><ins> -[<i>Note:</i> -Outstanding iterators, references and pointers may be invalidated. -— <i>end note</i>] -</ins></p> -</blockquote> -</blockquote> - - - - - -<hr> -<h3><a name="1036"></a>1036. Remove iterator specification that is redundant due to concept constraints</h3> -<p><b>Section:</b> 23.2.3 [sequence.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#sequence.reqmts">issues</a> in [sequence.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 231 [CD1]</b></p> - -<p> -p9-p11 are redundant now that Concepts define what it means to be an -Iterator and guide overload resolution accordingly. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Agree with issue and change to 23.2.3 [sequence.reqmts]. The -changes required to 21 [strings] will be part of the general -concept support for that clause. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Strike 23.2.3 [sequence.reqmts]p9-11. Make sure <tt>std::basic_string</tt> -has constraints similar to -<tt>std::vector</tt> to meet this old guarantee. -</p> - - - - - -<hr> -<h3><a name="1042"></a>1042. Provide <tt>ContiguousStorage</tt> concept and apply it to corresponding containers</h3> -<p><b>Section:</b> 23.3 [sequences] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#sequences">issues</a> in [sequences].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 244 [CD1]</b></p> - -<p> -The validity of the expression <tt>&a[n] == &a[0] + n</tt> is contingent on -<tt>operator&</tt> doing the "right thing" (as captured by the <tt>CopyConstructible</tt> -requirements in table 30 in C++2003). However this constraint has been -lost in the Concepts of C++0x. This applies to <tt>vector</tt> and <tt>array</tt> (it -actually applies to <tt>string</tt> also, but that's a different chapter, so I'll -file a separate comment there and cross-reference). -</p> - -<p> -Suggested solution: -</p> - -<p> -Define a <tt>ContiguousStorage</tt> and apply it to -<tt>vector</tt>, <tt>array</tt> and <tt>string</tt>. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote><p> -Agree with the issue but not the details of the proposed solution. Walter to -provide wording for the new concept. -</p></blockquote> - -<p><i>[ -Post Summit Alisdair adds: -]</i></p> - - -<blockquote><p> -Another LWG subgroup wondered if this concept should extend to <tt>complex<T></tt>, -and so not be built on the container concept at all? -</p></blockquote> - -<p><i>[ -2009-07 post-Frankfurt: -]</i></p> - - -<blockquote><p> -Leave Open, pending a post-Concepts Working Draft. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark issue 1042 as NAD, in rationale state that this was solved by removal of concepts. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add to <tt><container_concepts></tt> synopsis in [container.concepts] -</p> - -<blockquote><pre> -<ins>concept< typename C > ContiguousStorageContainer <i>see below</i>;</ins> -</pre></blockquote> - -<p> -Add a new section to the end of [container.concepts] -</p> - -<blockquote> -<p> -23.1.6.x ContiguousStorageContainer concept [container.concepts.contiguous] -</p> - -<pre> -concept ContiguousStorageContainer< typename C > - : Container<C> -{ - value_type* data(C&); - - axiom Contiguity(C& c, size_type i) { - if( i < size(c) ) { - addressof( * (data(c) + i) ) - == addressof( * advance(data(c), i) ); - } - } -} -</pre> - -<p> -The <tt>ContiguousStorageContainer</tt> concept describes a container whose elements -are allocated in a single region of memory, and are stored sequentially -without intervening padding other than to meet alignment requirements. -For example, the elements may be stored in a -single array of suitable length. -</p> - -<pre> -value_type * data( C& ); -</pre> - -<blockquote><p> -<i>Returns:</i> a pointer to the first element in the region of storage. -Result is unspecified for an empty container. -</p></blockquote> - -</blockquote> - -<p> -Change 23.3.2 [array] p1: -</p> - -<blockquote><p> --1- The header <tt><array></tt> defines a class template for -storing fixed-size sequences of objects. An <tt>array</tt> supports -random access iterators. An instance of <tt>array<T, N></tt> -stores <tt>N</tt> elements of type <tt>T</tt>, so that <tt>size() == -N</tt> is an invariant. The elements of an <tt>array</tt> are stored -contiguously, meaning that <del>if <tt>a</tt> is</del> an -<tt>array<T, N></tt> <del>then it obeys the identity <tt>&a[n] -== &a[0] + n</tt> for all <tt>0 <= n < N</tt></del> -<ins>satisfies the concept <tt>ContiguousStorageContainer< array<T, -N>></tt></ins>. -</p></blockquote> - -<p> -Add to the synopsis in 23.3.2 [array]: -</p> - -<blockquote><pre> - ... - T * data(); - const T * data() const; - }; - - <ins>template< typename T, size_t N ></ins> - <ins>concept_map ContiguousStorageContainer< array<T, N>> {};</ins> -} -</pre></blockquote> - -<p> -Change 23.3.6 [vector] p1: -</p> - -<blockquote><p> -A <tt>vector</tt> is a sequence container that supports random access -iterators. In addition, it supports (amortized) constant time insert and -erase operations at the end; insert and erase in the middle take linear -time. Storage management is handled automatically, though hints can be -given to improve efficiency. The elements of a vector are stored -contiguously, meaning that <del>if <tt>v</tt> is</del> a -<tt>vector<T, Alloc></tt> <ins>(</ins>where <tt>T</tt> is some -type other than <tt>bool</tt><ins>)</ins><del>, then it obeys the -identity <tt>&v[n] == &v[0] + n</tt> for all <tt>0 <= n < -v.size()</tt></del> <ins>satisfies the concept <tt>ContiguousStorageContainer< -vector< T, Alloc>></tt></ins>. -</p></blockquote> - -<p> -Add at the end of the synopsis in 23.3.6 [vector] p2: -</p> - -<blockquote><pre> -<ins>template< typename T, typename A > - requires !SameType< T, bool > - concept_map ContiguousStorageContainer< vector<T, A>> {};</ins> -</pre></blockquote> - - - -<p><b>Rationale:</b></p> -<p>Solved by removal of concepts.</p> - - - - - -<hr> -<h3><a name="1051"></a>1051. Specify subscript operation return types of <tt>reverse_iterator</tt> and <tt>move_iterator</tt></h3> -<p><b>Section:</b> 24.5.1.3.12 [reverse.iter.opindex], 24.5.3.3.12 [move.iter.op.index] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#reverse.iter.opindex">issues</a> in [reverse.iter.opindex].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 279 [CD1]</b></p> - -<p> -The reason the return type became unspecified is LWG issue <a href="lwg-defects.html#386">386</a>. This -reasoning no longer applies as there are at least two ways to get the right -return type with the new language facilities added since the previous -standard. -</p> - -<p> -Proposal: Specify the return type using either decltype or the Iter concept_map. -</p> - -<p><i>[ -Summit: -]</i></p> - - -<blockquote> -<p> -Under discussion. This is a general question about all iterator -adapters. -</p> -</blockquote> - -<p><i>[ -Howard adds post Summit: -]</i></p> - - -<blockquote><p> -I am requesting test cases to demonstrate a position. -</p></blockquote> - -<p><i>[ -2009-07-24 Daniel adds: -]</i></p> - - -<blockquote> -<p> -I recommend NAD. Without concepts we can no longer -restrict this member in a trivial way. Using <tt>decltype</tt> the -declaration would be along the lines of -</p> -<blockquote><pre> -static const Iter& __base(); // not defined -auto operator[](difference_type n) const -> decltype(__base()[-n-1]); -</pre></blockquote> - -<p> -but once <tt>reverse_iterator</tt> is instantiated for some given type -<tt>Iter</tt> which cannot form a well-formed expression <tt>__base()[-n-1]</tt> -this would cause an ill-formed function declaration, diagnostic -required, and no silent SFINAE elimination. -</p> - -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Moved to NAD. -</p></blockquote> - -<p><i>[ -2009-10-22 Daniel adds: -]</i></p> - - -<blockquote> -<p> -IMO, my original comment regarding ill-formedness of the described -construction is still correct, but I must add that I should weaken my -assertion "Without concepts we can no longer restrict this member in -a trivial way". -</p> - -<p> -In fact with the existence of default template arguments for function -templates it is not too hard to implement this like as follows, which -shows that we can indeed simulate to some sense constrained -member functions in C++0x. -</p> - -<p> -My example does not really proof that the specification is easy, but -it should be possible. I assume that the implementation would not -be ABI compatible, though. -</p> - -<p> -It is now your own decision how to proceed ;-) -</p> - -<blockquote><pre> -#include <type_traits> -#include <cstddef> - -template<class T> -typename std::add_rvalue_reference<T>::type declval(); - -template<class It> -struct reverse_iterator { - It base; - - typedef std::ptrdiff_t difference_type; - - template<class U = It, class Res = - decltype(declval<const U&>()[declval<difference_type>()]) - > - Res operator[](difference_type n) const { - return base[-n-1]; - } -}; - -struct MyIter { -}; - -int main() { - reverse_iterator<int*> ri; - ri[0] = 2; - reverse_iterator<MyIter> ri2; -} -</pre></blockquote> - -<p> -The above declaration could be simplified, but the ideal solution -</p> - -<blockquote><pre> -template<class U = It> - decltype(declval<const U&>()[declval<difference_type>()]) - operator[](difference_type n) const; -</pre></blockquote> - -<p> -does not work yet on gcc 4.4.1. -</p> - -</blockquote> - - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1056"></a>1056. Must all Engines and Distributions be Streamable?</h3> -<p><b>Section:</b> 26.5 [rand] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand">issues</a> in [rand].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Both the concepts <tt>RandomNumberEngine</tt> and <tt>RandomNumberDistribution</tt> have -requirements to be <tt>InputStreamable</tt> and <tt>OutputStreamable</tt>. -</p> -<p> -I have no problems leaving the WP in an inconsistent state on the best-faith -assumption these concepts will be provided later, however disagree with the -proposers that these constraints are not separable, orthogonal to the basic -concepts of generating random number distributions. -</p> -<p> -These constraints should be dropped, and applied to specific algorithms as -needed. -</p> -<p> -If a more refined concept (certainly deemed useful by the proposers) is -proposed there is no objection, but the basic concept should not require -persistence via streaming. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to Open. -</p></blockquote> - -<p><i>[ -2009-05-31 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -Working on constraining the stream iterators, I have a few more observations -to make on the concepts proposed while constraining the random number -facility. -</p> -<p> -While I still believe the concerns are orthogonal, I don't believe the -existing constraints go far enough either! The goal we want to achieve is -not that a <tt>RandomNumberEngine</tt> / <tt>RandomNumberDistribution</tt> supports the stream -operators, but that it is <tt>Serializable</tt>. I.e. there is a relationship -between the insert and extract operations that guarantees to restore the -state of the original object. This implies a coupling of the concepts -together in a broader concept (<tt>Serializable</tt>) with at least one axiom to -assert the semantics. -</p> -<p> -One problem is that <tt>istream</tt> and <tt>ostream</tt> may be fundamentally different -types, although we can hook a relation if we are prepared to drop down to -the <tt>char</tt> type and <tt>char_traits</tt> template parameters. Doing so ties us to a -form of serialization that demands implementation via the std iostreams -framework, which seems overly prescriptive. I believe the goal is generally -to support serialization without regard to how it is expressed - although -this is getting even more inventive in terms of concepts we do not have -today. -</p> -</blockquote> - -<p><i>[ -2009-11-03 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -I can't find the record in the wiki minutes, but it was agreed at both -Frankfurt and Santa Cruz that this issue is NAD. -</p> -<p> -The agreement in SC was that I would provide you with the rationale (see -below) to include when moving to NAD. -</p> -</blockquote> - -<p><i>[ -2009-11-03 Howard adds: -]</i></p> - - -<blockquote><p> -Moved to Tentatively NAD after 5 positive votes on c++std-lib. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p> -The issue suggests a more refined concept should be used if we want to -require streaming, to separate concerns from the basic -<tt>RandomNumberEngine</tt> behaviour. In Frankfurt it was observed -that <tt>RandomNumberEngine</tt> <em>is</em> that more refined concept, -and the basic concept used in the framework is -<tt>UniformRandomNumberGenerator</tt>, which it refines. -</p> - -<p> -We concur, and expect this to have no repurcussions re-writing this -clause now concepts are removed. -</p> - - - - - -<hr> -<h3><a name="1057"></a>1057. <tt>RandomNumberEngineAdaptor</tt></h3> -<p><b>Section:</b> 26.5 [rand] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand">issues</a> in [rand].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -The <tt>RandomNumberEngineAdaptor</tt> concept breaks precedent in the -way the library has been specified by grouping requirements into a -concept that is never actually used in the library. -</p> -<p> -This is undoubtedly a very helpful device for documentation, but we are not -comfortable with the precedent - especially as we have rejected national -body comments on the same grounds. -</p> -<p> -Suggest either removing the concept, or providing an algorithm/type that -requires this concept in their definition (such as a factory function to -create new engines). -</p> -<p> -The preference is to create a single new algorithm and retain the value of -the existing documentation. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Walter points out that it is unlikely that any algorithm would ever -require this concept, but that the concept nonetheless is useful as -documentation, and (via concept maps) as a means of checking specific adapters. -</p> -<p> -Alisdair disagrees as to the concept's value as documentation. -</p> -<p> -Marc points out that the <tt>RandomNumberDistribution</tt> -is also a concept not used elsewhere in the Standard. -</p> -<p> -Pete agrees that a policy of not inventing concepts -that aren't used in the Standard is a good starting point, -but should not be used as a criterion for rejecting a concept. -</p> -<p> -Move to Open. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1058"></a>1058. New container issue</h3> -<p><b>Section:</b> 23.2.3 [sequence.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#sequence.reqmts">issues</a> in [sequence.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Sequence containers 23.2.3 [sequence.reqmts]: -</p> - -<p> -The return value of new calls added to table 83 are not specified. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree with the proposed resolution. -</p> -<p> -Move to NAD Editorial. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Add after p6 23.2.3 [sequence.reqmts]: -</p> - -<blockquote> -<p> --6- ... -</p> -<p><ins> -The iterator returned from <tt>a.insert(p,rv)</tt> points to the copy of <tt>rv</tt> -inserted into <tt>a</tt>. -</ins></p> -<p><ins> -The iterator returned from <tt>a.emplace(p, args)</tt> points to the new -element constructed from <tt>args</tt> inserted into <tt>a</tt>. -</ins></p> -</blockquote> - - - - - -<hr> -<h3><a name="1059"></a>1059. Usage of no longer existing FunctionType concept</h3> -<p><b>Section:</b> 20.9.12.2 [func.wrap.func] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2009-03-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#func.wrap.func">active issues</a> in [func.wrap.func].</p> -<p><b>View all other</b> <a href="lwg-index.html#func.wrap.func">issues</a> in [func.wrap.func].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Due to a deliberate core language decision, the earlier called -"foundation" concept <tt>std::FunctionType</tt> had been removed in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2773.pdf">N2773</a> -shortly -before the first "conceptualized" version of the WP -(<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2798.pdf">N2798</a>) -had been -prepared. This caused a break of the library, which already used this -concept in the adapted definition of <tt>std::function</tt> -(20.9 [function.objects]/2, header <tt><functional></tt> synopsis and -20.9.12.2 [func.wrap.func]). -</p> -<p> -A simple fix would be to either (a) make <tt>std::function</tt>'s primary template -unconstrained or to (b) add constraints based on existing (support) concepts. -A more advanced fix would (c) introduce a new library concept. -</p> -<p> -The big disadvantage of (a) is, that users can define templates which -cause compiler errors during instantiation time because of under-constrainedness -and would thus violate the basic advantage of constrained -code. -</p> -<p> -For (b), the ideal constraints for <tt>std::function</tt>'s template parameter would -be one which excludes everything else but the single provided partial -specialization that matches every "free function" type (i.e. any function -type w/o cv-qualifier-seq and w/o ref-qualifier). -Expressing such a type as as single requirement would be written as -</p> -<blockquote><pre> -template<typename T> -requires ReferentType<T> // Eliminate cv void and function types with cv-qual-seq - // or ref-qual (depending on core issue #749) - && PointeeType<T> // Eliminate reference types - && !ObjectType<T> // Eliminate object types -</pre></blockquote> -<p> -Just for completeness approach (c), which would make sense, if the -library has more reasons to constrain for free function types: -</p> -<blockquote><pre> -auto concept FreeFunctionType<typename T> - : ReferentType<T>, PointeeType<T>, MemberPointeeType<T> -{ - requires !ObjectType<T>; -} -</pre></blockquote> -<p> -I mention that approach because I expect that free function types belong -to the most natural type categories for every days coders. Potential -candidates in the library are <tt>addressof</tt> and class template <tt>packaged_task</tt>. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Alisdair would prefer to have a core-supported <tt>FunctionType</tt> concept -in order that any future changes be automatically correct -without need for a library solution to catch up; -he points to type traits as a precedent. -Further, he believes that a published concept can't in the future -be changed. -</p> -<p> -Bill feels this category of entity would change sufficiently slowly -that he would be willing to take the risk. -</p> -<p> -Of the discussed solutions, we tend toward option (c). -We like the idea of having a complete taxonomy of native types, -and perhaps erred in trimming the set. -</p> -<p> -We would like to have this issue reviewed by Core and would like -their feedback. Move to Open. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -<p> -Change in 20.9 [function.objects]/2, Header <tt><functional></tt> synopsis: -</p> -<blockquote><pre> -// 20.6.16 polymorphic function wrappers: -class bad_function_call; -template<<del>FunctionType</del><ins>ReferentType F</ins>> -<ins>requires PointeeType<F> && !ObjectType<F></ins> -class function; // undefined -</pre></blockquote> -</li> -<li> -<p> -Change in 20.9.12.2 [func.wrap.func]: -</p> -<blockquote><pre> -namespace std { -template<<del>FunctionType</del><ins>ReferentType F</ins>> -<ins>requires PointeeType<F> && !ObjectType<F></ins> -class function; // undefined -</pre></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="1060"></a>1060. Embedded nulls in NTBS</h3> -<p><b>Section:</b> 17.5.2.1.4.1 [byte.strings] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Definition of null-terminated sequences allow for embedded nulls. This is -surprising, and probably not supportable with the intended use cases. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the issue, but believe this can be handled editorially. -Move to NAD Editorial. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1061"></a>1061. Bad indexing for tuple access to pair (Editorial?)</h3> -<p><b>Section:</b> 20.3.4 [pair.astuple] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -The definition of <tt>get</tt> implies that <tt>get</tt> must return the second element if -given a negative integer. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to NAD Editorial. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -20.3.4 [pair.astuple] p5: -</p> - -<blockquote><pre> -template<<del>int</del> <ins>size_t</ins> I, class T1, class T2> - requires True<(I < 2)> - const P& get(const pair<T1, T2>&); -</pre> -</blockquote> - - - - - - -<hr> -<h3><a name="1062"></a>1062. Missing insert_iterator for stacks/queues</h3> -<p><b>Section:</b> 24.5.2 [insert.iterators] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#insert.iterators">issues</a> in [insert.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -It is odd that we have an iterator to insert into a <tt>vector</tt>, but not an -iterator to insert into a <tt>vector</tt> that is adapted as a <tt>stack</tt>. The standard -container adapters all have a common interface to <tt>push</tt> and <tt>pop</tt> so it should -be simple to create an iterator adapter to complete the library support. -</p> - -<p> -We should provide an <tt>AdaptedContainer</tt> concept supporting <tt>push</tt> and <tt>pop</tt> -operations. Create a new insert iterator and factory function that inserts -values into the container by calling <tt>push</tt>. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Walter recommends NAD Future. -</p> -<p> -Move to Open, and recommend deferring the issue until after the next -Committee Draft is issued. -</p> -</blockquote> - -<p><i>[ -2009-07-29 Howard moves to Tentatively NAD Future. -]</i></p> - - -<blockquote><p> -A poll on the LWG reflector voted unanimously to move this issue to Tentatively NAD Future. -</p></blockquote> - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote><p> -Moved to NAD. The intent of these adapters are to restrict the interfaces. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1063"></a>1063. 03 iterator compatibilty</h3> -<p><b>Section:</b> X [iterator.backward] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Which header must a user <tt>#include</tt> to obtain the library-supplied -<tt>concept_maps</tt> declared in this paragraph? -</p> - -<p> -This is important information, as existing user code will break if this -header is not included, and we should make a point of mandating this header -is <tt>#include</tt>-d by library headers likely to make use of it, notably -<tt><algorithm></tt>. See issue <a href="lwg-closed.html#1001">1001</a> for more details. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the direction of the proposed resolution. -Move to Tentatively Ready. -</p></blockquote> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -We believe this is NAD Concepts, but this needs to be reviewed against the -post-remove-concepts draft. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p><i>Change [depr.lib.iterator.primitives], Iterator primitives, as -indicated:</i></p> - -<blockquote> - <p>To simplify the use of iterators and provide backward compatibility with - previous C++ Standard Libraries, - the library provides several classes and functions. <ins>Unless otherwise - specified, these classes and functions shall be defined in header <tt><iterator></tt>.</ins></p> -</blockquote> -<p><i>Change X [iterator.backward], Iterator backward compatibility, as -indicated:</i></p> -<blockquote> - <p>The library provides concept maps that allow iterators specified with - <tt>iterator_traits</tt> to interoperate with - algorithms that require iterator concepts. <ins>These concept maps shall be - defined in the same header that defines the iterator.</ins> [<i>Example:</i></p> -</blockquote> - - - - - -<hr> -<h3><a name="1064"></a>1064. Term "object state" should not refer to classes</h3> -<p><b>Section:</b> 17.3 [defns.obj.state] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-03-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 152 [CD1]</b></p> - -<p> -Object state is using a definition of object (instance of a class) from -outside the standard, rather than the 'region of storage' definiton in -1.8 [intro.object]p1 -</p> - -<p><i>[ -Summit: -]</i></p> - -<blockquote><p> -We think we're removing this; See X [func.referenceclosure.cons]. -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD. This will not affect user or implementer code -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="1067"></a>1067. simplified wording for inner_product</h3> -<p><b>Section:</b> 26.7 [numeric.ops] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#numeric.ops">issues</a> in [numeric.ops].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -One of the motivating examples for introducing requirements-aliases was to -simplify the wording of the <tt>inner_product</tt> requirements. As the paper -adopting the feature and constrained wording for the library went through in -the same meeting, it was not possible to make the change at the time. The -simpler form should be adopted now though. Similarly, most the other -numerical algorithms can benefit from a minor cleanup. -</p> -<p> -Note that in each case, the second more generalised form of the algorithm -does not benefit, as there are already named constraints supplied by the -template type parameters. -</p> - -<p><i>[ -2009-05-02 Daniel adds: -]</i></p> - - -<blockquote> -<p> -one part of the suggested resolution suggests the removal of the -<tt>MoveConstructible<T></tt> requirement from -<tt>inner_product</tt>. According to 26.7.3 [inner.product] -</p> - -<blockquote><p> -Computes its result by initializing the accumulator <tt>acc</tt> with the -initial value <tt>init</tt> -</p></blockquote> - -<p> -this step requires at least <tt>MoveConstructible</tt>. -</p> - -<p> -Therefore I strongly suggest to take this removal back (Note also -that the corresponding overload with a functor argument still has -the same <tt>MoveConstructible<T></tt> requirement). -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree with the proposed resolution as amended by Daniel's suggestion -to restore <tt>MoveConstructible</tt>, -reflected in the updated proposed resolution below. -</p> -<p> -Move to Tentatively Ready. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change in 26.7 [numeric.ops] and 26.7.2 [accumulate]: -</p> - -<blockquote><pre> -template <InputIterator Iter, MoveConstructible T> - requires <ins>add =</ins> HasPlus<T, Iter::reference> - && HasAssign<T, <del>HasPlus<T, Iter::reference></del> <ins>add</ins>::result_type> - T accumulate(Iter first, Iter last, T init); -</pre></blockquote> - -<p> -Change in 26.7 [numeric.ops] and 26.7.3 [inner.product]: -</p> - -<blockquote><pre> -template <InputIterator Iter1, InputIterator Iter2, MoveConstructible T> - requires <ins>mult =</ins> HasMultiply<Iter1::reference, Iter2::reference> - && <ins>add =</ins> HasPlus<T, <del>HasMultiply<Iter1::reference, Iter2::reference></del> <ins>mult</ins>::result_type> - && HasAssign< - T, - <del>HasPlus<T, - HasMultiply<Iter1::reference, Iter2::reference>::result_type></del> <ins>add</ins>::result_type> - T inner_product(Iter1 first1, Iter1 last1, Iter2 first2, T init); -</pre></blockquote> - -<p> -Change in 26.7 [numeric.ops] and 26.7.4 [partial.sum]: -</p> - -<blockquote><pre> -template <InputIterator InIter, OutputIterator<auto, const InIter::value_type&> OutIter> - requires <ins>add =</ins> HasPlus<InIter::value_type, InIter::reference> - && HasAssign<InIter::value_type, - <del>HasPlus<InIter::value_type, InIter::reference></del> <ins>add</ins>::result_type> - && Constructible<InIter::value_type, InIter::reference> - OutIter partial_sum(InIter first, InIter last, OutIter result); -</pre></blockquote> - -<p> -Change in 26.7 [numeric.ops] and 26.7.5 [adjacent.difference]: -</p> - -<blockquote><pre> -template <InputIterator InIter, OutputIterator<auto, const InIter::value_type&> OutIter> - requires <ins>sub =</ins> HasMinus<InIter::value_type, InIter::value_type> - && Constructible<InIter::value_type, InIter::reference> - && OutputIterator<OutIter, <del>HasMinus<InIter::value_type, InIter::value_type></del> <ins>sub</ins>::result_type> - && MoveAssignable<InIter::value_type> - OutIter adjacent_difference(InIter first, InIter last, OutIter result); -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1068"></a>1068. class <tt>random_device</tt> should be movable</h3> -<p><b>Section:</b> 26.5.6 [rand.device] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.device">issues</a> in [rand.device].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -class <tt>random_device</tt> should be movable. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to Open, and recommend this issue be deferred until after the next -Committee Draft is issued. -</p></blockquote> - -<p><i>[ -2009-10 post-Santa Cruz: -]</i></p> - - -<blockquote><p> -Leave open. Walter to provide drafting as part of his planned paper. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: Moved to NAD. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -WP is correct as written. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1069"></a>1069. class <tt>seed_seq</tt> should support efficient move operations</h3> -<p><b>Section:</b> 26.5.7.1 [rand.util.seedseq] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.util.seedseq">issues</a> in [rand.util.seedseq].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -class <tt>seed_seq</tt> should support efficient move operations. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to Open, and recommend this issue be deferred until after the next -Committee Draft is issued. -</p></blockquote> - -<p><i>[ -2009-10 post-Santa Cruz: -]</i></p> - - -<blockquote><p> -Leave open. Walter to provide drafting as part of his planned paper. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: -]</i></p> - - -<blockquote><p> -<tt>seed_seq</tt> is explicitly not copyable, so, much like LWG issue -<a href="lwg-closed.html#1068">1068</a>, LWG issue 1069 could be marked NAD to be consistent -with this. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1072"></a>1072. Is <tt>std::hash</tt> a constrained template or not?</h3> -<p><b>Section:</b> 20.9.13 [unord.hash] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#unord.hash">active issues</a> in [unord.hash].</p> -<p><b>View all other</b> <a href="lwg-index.html#unord.hash">issues</a> in [unord.hash].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Is <tt>std::hash</tt> a constrained template or not? -</p> -<p> -According to class template <tt>hash</tt> 20.9.13 [unord.hash], the definition is: -</p> - -<blockquote><pre> -template <class T> -struct hash : public std::unary_function<T, std::size_t> { - std::size_t operator()(T val) const; -}; -</pre></blockquote> - -<p> -And so unconstrained. -</p> -<p> -According to the <tt><functional></tt> synopsis in p2 Function objects -20.9 [function.objects] the template is declared as: -</p> - -<blockquote><pre> -template <ReferentType T> struct hash; -</pre></blockquote> - -<p> -which would make hash a constrained template. -</p> - -<p><i>[ -2009-03-22 Daniel provided wording. -]</i></p> - - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Alisdair is not certain that Daniel's proposed resolution is sufficient, -and recommends we leave the hash template unconstrained for now. -</p> -<p> -Recommend that the Project Editor make the constrained declaration consistent -with the definition in order to make the Working Paper internally consistent, -and that the issue then be revisited. -</p> -<p> -Move to Open. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> - -<p> -[To the editor: This resolution is merge-compatible to the -resolution of <a href="lwg-closed.html#1078">1078</a>] -</p> - -<ol> -<li> -<p> -In 20.9 [function.objects]/2, header <tt><functional></tt> synopsis, change as indicated: -</p> - -<blockquote><pre> -// 20.6.17, hash function base template: -template <ReferentType T> struct hash; <ins>// undefined</ins> -</pre></blockquote> -</li> -<li> -<p> -In 20.9.13 [unord.hash]/1 change as indicated: -</p> -<blockquote><pre> -namespace std { - <del>template <class T> - struct hash : public std::unary_function<T, std::size_t> { - std::size_t operator()(T val) const; - };</del> - <ins>template <ReferentType T> struct hash; // undefined</ins> -} -</pre></blockquote> -</li> -<li> -<p> -In 20.9.13 [unord.hash]/2 change as indicated: -</p> - -<blockquote><p> --2- <ins>For all library-provided specializations, the template -instantiation <tt>hash<T></tt> - shall provide a public <tt>operator()</tt> with return type <tt>std::size_t</tt> to -satisfy the concept - requirement <tt>Callable<const hash<T>, const T&></tt>. If <tt>T</tt> is an object -type or reference to - object, <tt>hash<T></tt> shall be publicly derived from -<tt>std::unary_function<T, std::size_t></tt>. - </ins> The return value of <tt>operator()</tt> is unspecified, except that -equal arguments - shall yield the same result. <tt>operator()</tt> shall not throw exceptions. -</p></blockquote> -</li> -<li> -<p> -In 18.7 [support.rtti]/1, header <tt><typeinfo></tt> synopsis change as indicated: -</p> -<blockquote><pre> -namespace std { - class type_info; - class type_index; - template <<del>class</del><ins>ReferentType</ins> T> struct hash; -</pre></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="1074"></a>1074. concept map broken by N2840</h3> -<p><b>Section:</b> X [allocator.element.concepts] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-19 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -p7 Allocator-related element concepts X [allocator.element.concepts] -</p> - -<p> -The changes to the <tt>AllocatableElement</tt> concept mean this <tt>concept_map</tt> -specialization no longer matches the original concept: -</p> - -<blockquote><pre> -template <Allocator Alloc, class T, class ... Args> - requires HasConstructor<T, Args...> - concept_map AllocatableElement<Alloc, T, Args&&...> { - void construct_element(Alloc& a, T* t, Args&&... args) { - Alloc::rebind<T>(a).construct(t, forward(args)...); - } - } -</pre></blockquote> - -<p><i>[ -2009-03-23 Pablo adds: -]</i></p> - - -<blockquote><p> -Actually, this is incorrect, -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2840.pdf">N2840</a> -says. "In section -X [allocator.element.concepts] paragraph 8, modify the definition of the -<tt>AllocatableElement</tt> concept and eliminate the related concept map:" but -then neglects to include the red-lined text of the concept map that was -to be eliminated. Pete also missed this, but I caught it he asked me to -review his edits. Pete's updated WP removes the concept map entirely, -which was the original intent. The issue is, therefore, moot. Note, as -per my presentation of -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2840.pdf">N2840</a> -in summit, <tt>construct()</tt> no longer has a -default implementation. This regrettable fact was deemed (by David -Abrahams, Doug, and myself) to be preferable to the complexity of -providing a default implementation that would not under-constrain a more -restrictive allocator (like the scoped allocators). -</p></blockquote> - -<p><i>[ -2009-05-01 Daniel adds: -]</i></p> - -<blockquote> -<p> -it seems to me that #1074 should be resolved as a NAD, because the -current WP has already removed the previous AllocatableElement concept map. -It introduced auto concept AllocatableElement instead, but as of -X [allocator.element.concepts]/7 this guy contains now -</p> -<blockquote><pre> -requires FreeStoreAllocatable<T>; -void Alloc::construct(T*, Args&&...); -</pre></blockquote> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -The affected code is no longer part of the Working Draft. -</p> -<p> -Move to NAD. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change X [allocator.element.concepts]: -</p> - -<blockquote><pre> -template <Allocator Alloc, class T, class ... Args> - requires HasConstructor<T, Args...> - concept_map AllocatableElement<Alloc, T, Args&&...> { - void construct_element(<del>Alloc& a,</del> T* t, Args&&... args) { - Alloc::rebind<T>(a).construct(t, forward(args)...); - } - } -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1076"></a>1076. unary/binary_negate need constraining and move support</h3> -<p><b>Section:</b> 20.9.9 [negators] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-03-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The class templates <tt>unary/binary_negate</tt> need constraining and move support. -</p> -<p> -Ideally these classes would be deprecated, allowing <tt>unary/binary_function</tt> to -also be deprecated. However, until a generic negate adaptor is introduced -that can negate any <tt>Callable</tt> type, they must be supported so should be -constrained. Likewise, they should be movable, and support adopting a -move-only predicate type. -</p> -<p> -In order to preserve ABI compatibility, new rvalue overloads are supplied in -preference to changing the existing pass-by-const-ref to pass-by-value. -</p> -<p> -Do not consider the issue of forwarding mutable lvalues at this point, -although remain open to another issue on the topic. -</p> - -<p><i>[ -2009-05-01 Daniel adds: -]</i></p> - -<blockquote> -<p> -IMO the currently proposed resolution needs some updates -because it is ill-formed at several places: -</p> - -<ol> -<li> -<p> -In concept AdaptableUnaryFunction change -</p> -<blockquote><pre> -typename X::result_type; -typename X::argument_type; -</pre></blockquote> -<p> -to -</p> -<blockquote><pre> -Returnable result_type = typename X::result_type; -typename argument_type = typename X::argument_type; -</pre></blockquote> -<p> -[The replacement "Returnable result_type" instead of "typename -result_type" is non-editorial, but maybe you prefer that as well] -</p> -</li> -<li> -<p> -In concept AdaptableBinaryFunction change -</p> -<blockquote><pre> -typename X::result_type; -typename X::first_argument_type; -typename X::second_argument_type; -</pre></blockquote> -<p> -to -</p> -<blockquote><pre> -Returnable result_type = typename X::result_type; -typename first_argument_type = typename X::first_argument_type; -typename second_argument_type = typename X::second_argument_type; -</pre></blockquote> -<p> -[The replacement "Returnable result_type" instead of "typename -result_type" is non-editorial, but maybe you prefer that as well.] -</p> -</li> - -<li> -<p> -In class unary/binary_function -</p> -<ol style="list-style-type:lower-alpha"> -<li> -I suggest to change "ReturnType" to "Returnable" in both cases. -</li> -<li> -I think you want to replace the remaining occurrences of "Predicate" by "P" -(in both classes in copy/move from a predicate) -</li> -</ol> -</li> -<li> -<p> -I think you need to change the proposed signatures of not1 and not2, because -they would still remain unconstrained: To make them constrained at least a -single requirement needs to be added to enable requirement implication. This -could be done via a dummy ("requires True<true>") or just explicit as follows: -</p> -<ol style="list-style-type:lower-alpha"> -<li> -<blockquote><pre> -template <AdaptableUnaryFunction P> -requires Predicate< P, P::argument_type> -unary_negate<P> not1(const P&& pred); -template <AdaptableUnaryFunction P> -requires Predicate< P, P::argument_type > -unary_negate<P> not1(P&& pred); -</pre> -<blockquote><p> --3- Returns: unary_negate<P>(pred). -</p></blockquote> -</blockquote> -<p> -[Don't we want a move call for the second overload as in -</p> -<blockquote><pre> -unary_negate<P>(std::move(pred)) -</pre></blockquote> -<p> -in the Returns clause ?] -</p> -</li> -<li> -<pre> -template <AdaptableBinaryFunction P> -requires Predicate< P, P::first_argument_type, P::second_argument_type > -binary_negate<P> not2(const P& pred); -template <AdaptableBinaryFunction P> -requires Predicate< P, P::first_argument_type, P::second_argument_type > -binary_negate<P> not2(P&& pred); -</pre> -<p> --5- Returns: binary_negate<P>(pred). -</p> -<p> -[Don't we want a move call for the second overload as in -</p> -<blockquote><pre> -binary_negate<P>(std::move(pred)) -</pre></blockquote> -<p> -in the Returns clause ?] -</p> -</li> -</ol> -</li> -</ol> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -There is concern that complicating the solution -to preserve the ABI seems unnecessary, -since we're not in general preserving the ABI. -</p> -<p> -We would prefer a separate paper consolidating all Clause 20 -issues that are for the purpose of providing constrained versions -of the existing facilities. -</p> -<p> -Move to Open. -</p> -</blockquote> - -<p><i>[ -2009-10 post-Santa Cruz: -]</i></p> - - -<blockquote><p> -Leave open pending the potential move constructor paper. Note that -we consider the "constraining" part NAD Concepts. -</p></blockquote> - -<p><i>[ -2010-01-31 Alisdair removes the current proposed wording from the proposed -wording section because it is based on concepts. That wording is proposed here: -]</i></p> - - -<blockquote class="note"> -<p> -Add new concepts where appropriate:: -</p> - -<blockquote><pre> -auto concept AdaptableUnaryFunction< typename X > { - typename X::result_type; - typename X::argument_type; -} - -auto concept AdaptableBinaryFunction< typename X > { - typename X::result_type; - typename X::first_argument_type; - typename X::second_argument_type; -} -</pre></blockquote> - -<p> -Revise as follows: -</p> - -<p> -Base [base] (Only change is constrained Result) -</p> - -<blockquote> -<p> --1- The following classes are provided to simplify the typedefs of the -argument and result types: -</p> -<pre> -namespace std { - template <class Arg, <del>class</del> <ins>ReturnType</ins> Result> - struct unary_function { - typedef Arg argument_type; - typedef Result result_type; - }; - - template <class Arg1, class Arg2, <del>class</del> <ins>ReturnType</ins> Result> - struct binary_function { - typedef Arg1 first_argument_type; - typedef Arg2 second_argument_type; - typedef Result result_type; - }; -} -</pre></blockquote> - -<p> -Negators 20.9.9 [negators]: -</p> - -<blockquote> -<p> --1- Negators <tt>not1</tt> and <tt>not2</tt> take a unary and a binary predicate, -respectively, and return their complements (5.3.1). -</p> - -<pre> -template <<del>class</del> <ins>AdaptableUnaryFunction</ins> P<del>redicate</del>> - <ins>requires Predicate< P, P::argument_type ></ins> - class unary_negate - : public unary_function<<del>typename</del> P<del>redicate</del>::argument_type,bool> { - public: - <ins>unary_negate(const unary_negate & ) = default;</ins> - <ins>unary_negate(unary_negate && );</ins> - - <ins>requires CopyConstructible< P ></ins> - explicit unary_negate(const Predicate& pred); - <ins>requires MoveConstructible< P > - explicit unary_negate(Predicate && pred);</ins> - - bool operator()(const <del>typename</del> P<del>redicate</del>::argument_type& x) const; - }; -</pre> -<blockquote><p> --2 <tt>operator()</tt> returns <tt>!pred(x)</tt>. -</p></blockquote> - -<pre> -template <class Predicate> - unary_negate<Predicate> not1(const Predicate&amp; pred); -<ins>template <class Predicate> - unary_negate<Predicate> not1(Predicate&& pred);</ins> -</pre> -<blockquote><p> --3- <i>Returns:</i> <tt>unary_negate<Predicate>(pred)</tt>. -</p></blockquote> - -<pre> -template <<del>class</del> <ins>AdaptableBinaryFunction</ins> P<del>redicate</del> > - <ins>requires Predicate< P, P::first_argument_type, P::second_argument_type ></ins> - class binary_negate - : public binary_function<<del>typename</del> P<del>redicate</del>::first_argument_type, - <del>typename</del> P<del>redicate</del>::second_argument_type, bool> { - public: - <ins>biary_negate(const binary_negate & ) = default;</ins> - <ins>binary_negate(binary_negate && );</ins> - - <ins>requires CopyConstructible< P ></ins> - explicit binary_negate(const Predicate& pred); - <ins>requires MoveConstructible< P > - explicit binary_negate(const Predicate& pred);</ins> - - bool operator()(const <del>typename</del> P<del>redicate</del>::first_argument_type& x, - const <del>typename</del> P<del>redicate</del>::second_argument_type& y) const; - }; -</pre> -<blockquote><p> --4- <tt>operator()</tt> returns <tt>!pred(x,y)</tt>. -</p></blockquote> - -<pre> -template <class Predicate> - binary_negate<Predicate> not2(const Predicate& pred); -<ins>template <class Predicate> - binary_negate<Predicate> not2(Predicate&& pred);</ins> -</pre> - -<blockquote><p> --5- <i>Returns:</i> <tt>binary_negate<Predicate>(pred)</tt>. -</p></blockquote> -</blockquote> - -</blockquote> - - -<p><i>[ -2010 Rapperswil: -]</i></p> - - -<blockquote><p> -Move to NAD Concepts. The move-semantic part has been addressed by a core language change, -which implicitly generates appropriate move constructors and move-assignment operators. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1077"></a>1077. Nonesense <tt>tuple</tt> declarations</h3> -<p><b>Section:</b> 20.4.2 [tuple.tuple] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2009-03-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#tuple.tuple">issues</a> in [tuple.tuple].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Class template tuple 20.4.2 [tuple.tuple]: -</p> - -<blockquote><pre> -template <class... UTypes> - requires Constructible<Types, const UTypes&>... -template <class... UTypes> - requires Constructible<Types, RvalueOf<UTypes>::type>... -</pre></blockquote> - -<p> -Somebody needs to look at this and say what it should be. -</p> - -<p><i>[ -2009-03-21 Daniel provided wording. -]</i></p> - - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -The resolution looks correct; move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -In 20.4.2 [tuple.tuple], class <tt>tuple</tt>, change as indicated: -</p> - -<blockquote><pre> -template <class... UTypes> - requires Constructible<Types, const UTypes&>... - <ins>tuple(const pair<UTypes...>&);</ins> -template <class... UTypes> - requires Constructible<Types, RvalueOf<UTypes>::type>... - <ins>tuple(pair<UTypes...>&&);</ins> -</pre></blockquote> - -<p> -[NB.: The corresponding prototypes do already exist in 20.4.2.1 [tuple.cnstr]/7+8] -</p> - - - - - -<hr> -<h3><a name="1078"></a>1078. DE-17: Remove class type_index</h3> -<p><b>Section:</b> 20.14 [type.index] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Doug Gregor <b>Opened:</b> 2009-03-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#type.index">issues</a> in [type.index].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses DE 17</b></p> - -<p> -DE-17: -</p> -<p> -The class <tt>type_index</tt> should be removed; it provides no additional -functionality beyond providing appropriate concept maps. -</p> - -<p><i>[ -2009-03-31 Peter adds: -]</i></p> - - -<blockquote> -<p> -It is not true, in principle, that <tt>std::type_index</tt> provides no utility -compared to bare <tt>std::type_info*</tt>. -</p> -<p> -<tt>std::type_index</tt> can avoid the lifetime issues with <tt>type_info</tt> when the -DLL that has produced the <tt>type_info</tt> object is unloaded. A raw -<tt>type_info*</tt> does not, and cannot, provide any protection in this case. -A <tt>type_index</tt> can (if the implementor so chooses) because it can wrap a -smart (counted or even cloning) pointer to the <tt>type_info</tt> data that is -needed for <tt>name()</tt> and <tt>before()</tt> to work. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p>Modify the header <typeinfo> synopsis in - 18.7 [support.rtti]p1 as follows:</p> - -<blockquote><pre> -namespace std { - class type_info; - <del>class type_index;</del> - template <class T> struct hash; - template<> struct hash<<del>type_index</del><ins>const type_info *</ins>> : public std::unary_function<<del>type_index</del><ins>const type_info *</ins>, size_t> { - size_t operator()(<del>type_index</del><ins>const type_info *</ins> <del>index</del><ins>t</ins>) const; - }<ins>;</ins> - <ins>concept_map LessThanComparable<const type_info *> <i>see below</i></ins> - class bad_cast; - class bad_typeid; -} -</pre></blockquote> - -<p>Add the following new subsection</p> -<blockquote> -<p> -<ins>18.7.1.1 Template specialization <code>hash<const type_info *></code> -[type.info.hash]</ins></p> - -<pre> -<ins>size_t operator()(const type_info *x) const;</ins> -</pre> -<ol> -<li><ins><i>Returns</i>: <code>x->hash_code()</code></ins></li> -</ol> -</blockquote> - - <p>Add the following new subsection</p> - <blockquote> -<p><ins>18.7.1.2 <code>type_info</code> concept map [type.info.concepts]</ins></p> - - -<pre> -<ins>concept_map LessThanComparable<const type_info *> {</ins> - <ins>bool operator<(const type_info *x, const type_info *y) { return x->before(*y); }</ins> - <ins>bool operator<=(const type_info *x, const type_info *y) { return !y->before(*x); }</ins> - <ins>bool operator>(const type_info *x, const type_info *y) { return y->before(*x); }</ins> - <ins>bool operator>=(const type_info *x, const type_info *y) { return !x->before(*y); }</ins> -<ins>}</ins> -</pre> -<ol> - <li><ins><i>Note</i>: provides a well-defined ordering among - <code>type_info const</code> pointers, which makes such pointers - usable in associative containers (23.4).</ins></li> -</ol> -</blockquote> - -<p>Remove section 20.14 [type.index]</p> - - - - - -<hr> -<h3><a name="1080"></a>1080. Concept ArithmeticLike should provide explicit boolean conversion</h3> -<p><b>Section:</b> X [concept.arithmetic] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2009-03-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Astonishingly, the current concept ArithmeticLike as specified in -X [concept.arithmetic] does not provide explicit conversion -to <tt>bool</tt> although this is a common property of arithmetic types -(4.12 [conv.bool]). Recent proposals that introduced such types -(integers of arbitrary precision, -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2143.pdf">n2143</a>, -decimals -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2732.pdf">n2732</a> -indirectly -via conversion to <tt>long long</tt>) also took care of such a feature. -</p> -<p> -Adding such an explicit conversion associated function would also -partly solve a currently invalid effects clause in library, which bases -on this property, 24.2.7 [random.access.iterators]/2: -</p> -<blockquote><pre> -{ difference_type m = n; - if (m >= 0) while (m--) ++r; - else while (m++) --r; - return r; } -</pre></blockquote> - -<p> -Both while-loops take advantage of a contextual conversion to <tt>bool</tt> -(Another problem is that the >= comparison uses the no -longer supported existing implicit conversion from <tt>int</tt> to <tt>IntegralLike</tt>). -</p> - -<p><b>Original proposed resolution:</b></p> -<ol> -<li> -<p> -In X [concept.arithmetic], add to the list of less refined -concepts one further concept: -</p> - -<blockquote><pre> -concept ArithmeticLike<typename T> - : Regular<T>, LessThanComparable<T>, HasUnaryPlus<T>, HasNegate<T>, - HasPlus<T, T>, HasMinus<T, T>, HasMultiply<T, T>, HasDivide<T, T>, - HasPreincrement<T>, HasPostincrement<T>, HasPredecrement<T>, - HasPostdecrement<T>, - HasPlusAssign<T, const T&>, HasMinusAssign<T, const T&>, - HasMultiplyAssign<T, const T&>, - HasDivideAssign<T, const T&><ins>, ExplicitlyConvertible<T, bool></ins> { -</pre></blockquote> -</li> -<li> -<p> -In 24.2.7 [random.access.iterators]/2 change the current effects clause -as indicated [The proposed insertion fixes the problem that the previous -implicit construction from integrals has been changed to an explicit -constructor]: -</p> -<blockquote><pre> -{ difference_type m = n; - if (m >= <ins>difference_type(</ins>0<ins>)</ins>) while (m--) ++r; - else while (m++) --r; - return r; } -</pre></blockquote> -</li> -</ol> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree that arithmetic types ought be convertible to <tt>bool</tt>, -and we therefore agree with the proposed resolution's paragraph 1. -</p> -<p> -We do not agree that the cited effects clause is invalid, -as it expresses intent rather than specific code. -</p> -<p> -Move to Review, pending input from concepts experts. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -In X [concept.arithmetic], add to the list of less refined -concepts one further concept: -</p> - -<blockquote><pre> -concept ArithmeticLike<typename T> - : Regular<T>, LessThanComparable<T>, HasUnaryPlus<T>, HasNegate<T>, - HasPlus<T, T>, HasMinus<T, T>, HasMultiply<T, T>, HasDivide<T, T>, - HasPreincrement<T>, HasPostincrement<T>, HasPredecrement<T>, - HasPostdecrement<T>, - HasPlusAssign<T, const T&>, HasMinusAssign<T, const T&>, - HasMultiplyAssign<T, const T&>, - HasDivideAssign<T, const T&><ins>, ExplicitlyConvertible<T, bool></ins> { -</pre></blockquote> - - - - - -<hr> -<h3><a name="1081"></a>1081. <tt>basic_string</tt> needs to be a concept-constrained template</h3> -<p><b>Section:</b> 21 [strings] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#strings">issues</a> in [strings].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses UK 216, JP 46, JP 48 [CD1]</b></p> - -<p> -All the containers use concepts for their iterator usage, exect for -<tt>basic_string</tt>. This needs fixing. -</p> - -<p> -Use concepts for iterator template parameters throughout the chapter. -</p> - -<p><i>[ -Summit: -]</i></p> - -<blockquote><p> -NB comments to be handled by Dave Abrahams and Howard Hinnant with -advice from PJP: UK216 (which duplicates) JP46, JP48. JP46 supplies -extensive proposed wording; start there. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1082"></a>1082. <tt>codecvt</tt> needs to be a concept-constrained template</h3> -<p><b>Section:</b> 22 [localization] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#localization">issues</a> in [localization].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses JP 49 [CD1]</b></p> - -<p> -<tt>codecvt</tt> does not use concept. For example, create <tt>CodeConvert</tt> -concept and change as follows. -</p> - -<blockquote><pre> -template<CodeConvert Codecvt, class Elem = wchar_t> - class wstring_convert { -</pre></blockquote> - -<p><i>[ -Summit: -]</i></p> - -<blockquote><p> -To be handled by Howard Hinnant, Dave Abrahams, Martin Sebor, PJ Plauger. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1083"></a>1083. <tt>InputIterator</tt> and <tt>OutputIterator</tt> template parameters need to be concept constraints</h3> -<p><b>Section:</b> 22 [localization] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#localization">issues</a> in [localization].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses JP 52, JP 53 [CD1]</b></p> - -<p> -<tt>InputIterator</tt> does not use concept. -</p> - -<p> -<tt>OutputIterator</tt> does not use concept. -</p> - -<p> -Comments include proposed wording. -</p> - -<p><i>[ -Summit: -]</i></p> - -<blockquote><p> -To be handled by Howard Hinnant, Dave Abrahams, Martin Sebor, PJ Plauger. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1084"></a>1084. Concept <tt>ForwardIterator</tt> should provide default implementation for post-increment</h3> -<p><b>Section:</b> 24.2.5 [forward.iterators] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#forward.iterators">issues</a> in [forward.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses UK 250 [CD1]</b></p> - -<p> -A default implementation should be supplied for the post-increment -operator to simplify implementation of iterators by users. -</p> - -<p> -Copy the Effects clause into the concept description as the default -implementation. Assumes a default value for <tt>postincrement_result</tt>. -</p> - -<p><i>[ -Summit: -]</i></p> - -<blockquote><p> -Howard will open an issue. -</p></blockquote> - -<p><i>[ -2009-06-07 Daniel adds: -]</i></p> - - -<blockquote><p> -This issue cannot currently be resolved as suggested, because -that would render auto-detection of the return type -<tt>postincrement_result</tt> invalid, see [concept.map.assoc]/4+5. The -best fix would be to add a default type to that associated type, but -unfortunately any default type will prevent auto-deduction of types of -associated functions as quoted above. A corresponding core issue -is in preparation. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p><i>[ -This wording assumes the acceptance of UK 251 / <a href="lwg-closed.html#1009">1009</a>. Both -wordings change the same paragraphs. -]</i></p> - - -<p> -Change 24.2.5 [forward.iterators]: -</p> - -<blockquote> -<pre> -concept ForwardIterator<typename X> : InputIterator<X>, Regular<X> { - - MoveConstructible postincrement_result; - requires HasDereference<postincrement_result> - && Convertible<HasDereference<postincrement_result>::result_type, const value_type&>; - - postincrement_result operator++(X& r, int)<del>;</del> <ins>{ - X tmp = r; - ++r; - return tmp; - }</ins> - - axiom MultiPass(X a, X b) { - if (a == b) *a == *b; - if (a == b) ++a == ++b; - } -} -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1085"></a>1085. <tt>BidirectionalIterator</tt> concept should provide default implementation for post-decrement</h3> -<p><b>Section:</b> 24.2.6 [bidirectional.iterators] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#bidirectional.iterators">issues</a> in [bidirectional.iterators].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses UK 258 [CD1]</b></p> - -<p> -A default implementation should be supplied for the post-decrement -operator to simplify implementation of iterators by users. -</p> - -<p> -Copy the Effects clause into the concept description as the default -implementation. Assumes a default value for <tt>postincrement_result</tt>. -</p> - -<p><i>[ -Summit: -]</i></p> - -<blockquote><p> -Howard will open an issue. -</p></blockquote> - -<p><i>[ -2009-06-07 Daniel adds: -]</i></p> - - -<blockquote><p> -This issue cannot currently be resolved as suggested, because -that would render auto-detection of the return type -<tt>postdecrement_result</tt> invalid, see <a href="lwg-closed.html#1084">1084</a>. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - -<p> -Change 24.2.6 [bidirectional.iterators]: -</p> - -<blockquote> -<pre> -concept BidirectionalIterator<typename X> : ForwardIterator<X> { - MoveConstructible postdecrement_result; - requires HasDereference<postdecrement_result> - && Convertible<HasDereference<postdecrement_result>::result_type, const value_type&> - && Convertible<postdecrement_result, const X&>; - X& operator--(X&); - postdecrement_result operator--(X& <ins>r</ins>, int)<del>;</del> <ins>{ - X tmp = r; - --r; - return tmp; - }</ins> -} -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1086"></a>1086. Stream iterators need to be concept-constrained templates</h3> -<p><b>Section:</b> 24.6 [stream.iterators] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses UK 284 [CD1]</b></p> - -<p> -The stream iterators need constraining with concepts/requrires clauses. -</p> - -<p><i>[ -Summit: -]</i></p> - -<blockquote><p> -We agree. To be handled by Howard, Martin and PJ. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1087"></a>1087. Incorrect <tt>OutputIterator</tt> concept requirements for <tt>replace</tt> algorithms</h3> -<p><b>Section:</b> 25.3.5 [alg.replace] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.replace">issues</a> in [alg.replace].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses UK 301 [CD1]</b></p> - -<p> -<tt>replace</tt> and <tt>replace_if</tt> have the requirement: <tt>OutputIterator<Iter, -Iter::reference></tt> Which implies they need to copy some values in the -range the algorithm is iterating over. This is not however the case, the -only thing that happens is <tt>const T&</tt>s might be copied over existing -elements (hence the <tt>OutputIterator<Iter, const T&></tt>. -</p> - -<p> -Remove <tt>OutputIterator<Iter, Iter::reference></tt> from <tt>replace</tt> -and <tt>replace_if</tt>. -</p> - -<p><i>[ -Summit: -]</i></p> - -<blockquote><p> -We agree. To be handled by Howard. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change in [algorithms.syn] and 25.3.5 [alg.replace]: -</p> - -<blockquote><pre> -template<ForwardIterator Iter, class T> - requires <del>OutputIterator<Iter, Iter::reference> - &&</del> OutputIterator<Iter, const T&> - && HasEqualTo<Iter::value_type, T> - void replace(Iter first, Iter last, - const T& old_value, const T& new_value); - -template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred, class T> - requires <del>OutputIterator<Iter, Iter::reference> - &&</del> OutputIterator<Iter, const T&> - && CopyConstructible<Pred> - void replace_if(Iter first, Iter last, - Pred pred, const T& new_value); -</pre></blockquote> - - - - - -<hr> -<h3><a name="1091"></a>1091. Multimap description confusing</h3> -<p><b>Section:</b> 23.4.5.3 [multimap.modifiers] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> LWG <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 246</b></p> -<p> -The content of this sub-clause is purely trying to describe in words the -effect of the requires clauses on these operations, now that we have -Concepts. As such, the description is more confusing than the signature -itself. The semantic for these functions is adequately covered in the -requirements tables in 23.2.4 [associative.reqmts]. -</p> - -<p><i>[ -Beman adds: -]</i></p> - - -<blockquote><p> -Pete is clearly right that -this one is technical rather than editorial. -</p></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree with the proposed resolution. -</p> -<p> -Move to Review. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD, solved by removing concepts. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Strike 23.4.5.3 [multimap.modifiers] entirely -(but do NOT strike these signatures from the class template definition!). -</p> - - - - - -<hr> -<h3><a name="1092"></a>1092. Class template <tt>integral_constant</tt> should be a constrained template</h3> -<p><b>Section:</b> 20.10.3 [meta.help] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2009-03-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.help">issues</a> in [meta.help].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -A first step to change the type traits predicates to constrained templates is to -constrain their common base template <tt>integral_constant</tt>. This can be done, -without enforcing depending classes to be constrained as well, but not -vice versa -without brute force <tt>late_check</tt> usages. The following proposed resolution depends -on the resolution of LWG issue <a href="lwg-defects.html#1019">1019</a>. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to Open, pending a paper that looks at constraints -for the entirety of the type traits -and their relationship to the foundation concepts. -We recommend this be deferred -until after the next Committee Draft is issued. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -<p> -In 20.10.2 [meta.type.synop], Header <tt><type_traits></tt> -synopsis change as indicated: -</p> -<blockquote><pre> -namespace std { -// 20.5.3, helper class: -template <<del>class</del><ins>IntegralConstantExpressionType</ins> T, T v> struct integral_constant; -</pre></blockquote> -</li> -<li> -<p> -In 20.10.3 [meta.help] change as indicated: -</p> -<blockquote><pre> -template <<del>class</del><ins>IntegralConstantExpressionType</ins> T, T v> -struct integral_constant { - static constexpr T value = v; - typedef T value_type; - typedef integral_constant<T,v> type; - constexpr operator value_type() { return value; } -}; -</pre></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="1096"></a>1096. unconstrained rvalue ref parameters</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2009-03-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -TODO: Look at all cases of unconstrained rvalue ref parameters and check -that concept req'ts work when <tt>T</tt> deduced as reference. -</p> - -<p> - We found some instances where that was not done correctly and we figure - the possibility of deducing <tt>T</tt> to be an lvalue reference was probably - overlooked elsewhere. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to Open, pending proposed wording from Dave for further review. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="1099"></a>1099. Various issues</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2009-03-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Notes -</p> -<blockquote> -<p> -[2009-03-21 Sat] p. 535 at the top we need MoveConstructible V1, -MoveConstructible V2 (where V1,V2 are defined on 539). Also make_tuple -on 550 -</p> - -<blockquote> -<p> -CD-1 reads: -</p> - -<blockquote><pre> -template <MoveConstructible T1, MoveConstructible T2> -pair<V1, V2> make_pair(T1&&, T2&&); -</pre></blockquote> - -<p> -Actually I'm guessing we need something like <tt>MoveConstructible<V1,T1></tt>, -i.e. "<tt>V1</tt> can be constructed from an rvalue of type <tt>T1</tt>." -</p> - -<p> -Ditto for <tt>make_tuple</tt> -</p> -</blockquote> - -<p> -[2009-03-21 Sat] p1183 thread ctor, and in general, we need a way to -talk about "copiable from generalized rvalue ref argument" for cases -where we're going to forward and copy. -</p> -<blockquote> -<p> - This issue may well be quite large. Language in para 4 about "if - an lvalue" is wrong because types aren't expressions. -</p> - -<blockquote> -<p> -Maybe we should define the term "move" so we can just say in the -effects, "<tt>f</tt> is moved into the newly-created thread" or something, and -agree (and ideally document) that saying "<tt>f</tt> is moved" implies -</p> - -<blockquote><pre> -F x(move(f)) -</pre></blockquote> - -<p> -is required to work. That would cover both ctors at once. -</p> -</blockquote> - -<p> - p1199, call_once has all the same issues. -</p> -</blockquote> -<p> -[2009-03-21 Sat] p869 InputIterator pointer type should not be required -to be convertible to const value_type*, rather it needs to have a -operator-> of its own that can be used for the value type. -</p> - -<blockquote><p> -This one is serious and unrelated to the move issue. -</p></blockquote> - -<p> -[2009-03-21 Sat] p818 stack has the same problem with default ctor. -</p> -<p> -[2009-03-21 Sat] p816 priority_queue has the same sorts of problems as queue, only more so -</p> -<blockquote><pre> - requires MoveConstructible<Cont> - explicit priority_queue(const Compare& x = Compare(), Cont&& = Cont()); -</pre> -<p> - Don't require MoveConstructible when default constructing Cont. - Also missing semantics for move ctor. -</p> -</blockquote> -<p> - [2009-03-21 Sat] Why are Allocators required to be CopyConstructible as - opposed to MoveConstructible? -</p> -<p> - [2009-03-21 Sat] p813 queue needs a separate default ctor (Cont needn't - be MoveConstructible). No documented semantics for move c'tor. Or - *any* of its 7 ctors! -</p> -<p> - [2009-03-21 Sat] std::array should have constructors for C++0x, - consequently must consider move construction. -</p> - -<p><i>[ -2009-05-01 Daniel adds: -]</i></p> - - -<blockquote><p> -This could be done as part of <a href="lwg-closed.html#1035">1035</a>, which already handles -deviation of <tt>std::array</tt> from container tables. -</p></blockquote> - -<p> - [2009-03-21 Sat] p622 all messed up. -</p> -<blockquote> -<p> - para 8 "implementation-defined" is the wrong term; should be "see - below" or something. -<p/> - para 12 "will be selected" doesn't make any sense because we're not - talking about actual arg types. -<p/> - paras 9-13 need to be totally rewritten for concepts. -</p> -</blockquote> - -<p> - [2009-03-21 Sat] Null pointer comparisons (p587) have all become - unconstrained. Need to fix that -<p/> - [2009-03-21 Sat] mem_fun_t etc. definition doesn't match declaration. - We think CopyConstructible is the right reqt. -<p/> - make_pair needs Constructible<V1, T1&&> requirements! -<p/> - make_tuple needs something similar -<p/> - tuple bug in synopsis: -</p> -<blockquote><pre> - template <class... UTypes> - requires Constructible<Types, const UTypes&>... - template <class... UTypes> - requires Constructible<Types, RvalueOf<UTypes>::type>... -</pre> -<p> - Note: removal of MoveConstructible requirements in std::function makes - these routines unconstrained! -</p> -</blockquote> - -<p><i>[ -2009-05-02 Daniel adds: -]</i></p> - - -<blockquote><p> -This part of the issue is already covered by <a href="lwg-closed.html#1077">1077</a>. -</p></blockquote> - -<p> - these unique_ptr constructors are broken [ I think this is covered in "p622 all messed up" ] -</p> -<blockquote><pre> - unique_ptr(pointer p, implementation-defined d); - unique_ptr(pointer p, implementation-defined d); -</pre></blockquote> -<p> - multimap range constructor should not have MoveConstructible<value_type> requirement. -</p> -<blockquote><p> - same with <tt>insert(..., P&&);</tt> <tt>multiset</tt> has the same issue, as do - <tt>unordered_multiset</tt> and <tt>unordered_multimap</tt>. Review these! -</p></blockquote> - -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -Move to Open, pending proposed wording from Dave for further review. -</p></blockquote> - -<p><i>[ -2009-10 post-Santa Cruz: -]</i></p> - - -<blockquote><p> -Tentatively NAD. We are not sure what has been addressed and what hasn't. -Recommend closing unless someone sorts this out into something more readable. -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p> -The issue(s) at hand not adequately communicated. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="1101"></a>1101. <tt>unique</tt> requirements</h3> -<p><b>Section:</b> 25.3.9 [alg.unique] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-04-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.unique">issues</a> in [alg.unique].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -From Message c++std-core-14160 Howard wrote: -</p> - -<blockquote><p> -It was the intent of the rvalue reference proposal for unique to only require MoveAssignable: -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1860.html#25.2.9%20-%20Unique">N1860</a>. -</p></blockquote> - -<p> -And Pete replied: -</p> - -<blockquote><p> -That was overridden by the subsequent changes made for concepts in -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2573.pdf">N2573</a>, -which reimposed the C++03 requirements. -</p></blockquote> - -<p> -My impression is that this overwrite was a simple (unintentional) mistake. -Wording below to correct it. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Howard notes this issue resolves a discrepancy between the synopsis -and the description. -</p> -<p> -Move to NAD Editorial. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 25.3.9 [alg.unique]: -</p> - -<blockquote><pre> -template<ForwardIterator Iter> - requires OutputIterator<Iter, <ins>RvalueOf<</ins>Iter::reference<ins>>::type</ins>> - && EqualityComparable<Iter::value_type> - Iter unique(Iter first, Iter last); - -template<ForwardIterator Iter, EquivalenceRelation<auto, Iter::value_type> Pred> - requires OutputIterator<Iter, RvalueOf<Iter::reference>::type> - && CopyConstructible<Pred> - Iter unique(Iter first, Iter last, Pred pred); -</pre></blockquote> - -<p> -Note that the synopsis in [algorithms.syn] is already correct. -</p> - - - - - - -<hr> -<h3><a name="1102"></a>1102. <tt>std::vector</tt>'s reallocation policy still unclear</h3> -<p><b>Section:</b> 23.3.6.3 [vector.capacity] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2009-04-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#vector.capacity">active issues</a> in [vector.capacity].</p> -<p><b>View all other</b> <a href="lwg-index.html#vector.capacity">issues</a> in [vector.capacity].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I have the impression that even the wording of current draft -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2857.pdf">N2857</a> -does insufficiently express the intent of <tt>vector</tt>'s -reallocation strategy. This has produced not too old library -implementations which release memory in the <tt>clear()</tt> function -and even modern articles about C++ programming cultivate -the belief that <tt>clear</tt> is allowed to do exactly this. A typical -example is something like this: -</p> - -<blockquote><pre> -const int buf_size = ...; -std::vector<T> buf(buf_size); -for (int i = 0; i < some_condition; ++i) { - buf.resize(buf_size); - write_or_read_data(buf.data()); - buf.clear(); // Ensure that the next round get's 'zeroed' elements -} -</pre></blockquote> -<p> -where still the myth is ubiquitous that <tt>buf</tt> might be -allowed to reallocate it's memory *inside* the <tt>for</tt> loop. -</p> -<p> -IMO the problem is due to the fact, that -</p> - -<ol style="list-style-type:lower-alpha"> -<li> -the actual memory-reallocation stability of <tt>std::vector</tt> -is explained in 23.3.6.3 [vector.capacity]/3 and /6 which -are describing just the effects of the <tt>reserve</tt> -function, but in many examples (like above) there -is no explicit call to <tt>reserve</tt> involved. Further-more -23.3.6.3 [vector.capacity]/6 does only mention <em>insertions</em> -and never mentions the consequences of erasing -elements. -</li> -<li> -<p> -the effects clause of <tt>std::vector</tt>'s <tt>erase</tt> overloads in -23.3.6.5 [vector.modifiers]/4 is silent about capacity changes. This -easily causes a misunderstanding, because the counter -parting insert functions described in 23.3.6.5 [vector.modifiers]/2 -explicitly say, that -</p> -<blockquote><p> -Causes reallocation if the new size is greater than the -old capacity. If no reallocation happens, all the iterators -and references before the insertion point remain valid. -</p></blockquote> -<p> -It requires a complex argumentation chain about four -different places in the standard to provide the - possibly -weak - proof that calling <tt>clear()</tt> also does <em>never</em> change -the capacity of the <tt>std::vector</tt> container. Since <tt>std::vector</tt> -is the de-facto replacement of C99's dynamic arrays this -type is near to a built-in type and it's specification should -be clear enough that usual programmers can trust their -own reading. -</p> -</li> -</ol> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -Bill believes paragraph 1 of the proposed resolution is unnecessary -because it is already implied (even if tortuously) by the current wording. -</p> -<p> -Move to Review. -</p> -</blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD. Rationale: there is no consensus to clarify the standard, -general consensus that the standard is correct as written. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p><i>[ -This is a minimum version. I also -suggest that the wording explaining the allocation strategy -of <tt>std::vector</tt> in 23.3.6.3 [vector.capacity]/3 and /6 is moved into -a separate sub paragraph of 23.3.6.3 [vector.capacity] <em>before</em> -any of the prototype's are discussed, but I cannot provide -reasonable wording changes now -]</i></p> - - -<ol> -<li> -<p> -Change 23.3.6.3 [vector.capacity]/6 as follows: -</p> -<blockquote><p> -It is guaranteed that no reallocation takes place during -insertions <ins>or erasures</ins> that happen after a call -to <tt>reserve()</tt> until the time when an insertion would make -the size of the vector greater than the value of <tt>capacity()</tt>. -</p></blockquote> -</li> -<li> -<p> -Change 23.3.6.5 [vector.modifiers]/4 as follows: -</p> -<blockquote><p> -<i>Effects:</i> <ins>The capacity shall remain unchanged and no reallocation shall -happen.</ins> -Invalidates iterators and references at or after the point -of the erase. -</p></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="1105"></a>1105. Shouldn't <tt>Range</tt> be an <tt>auto concept</tt></h3> -<p><b>Section:</b> X [iterator.concepts.range] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2009-04-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><i>[ -2009-04-26 Herb adds: -]</i></p> - - -<blockquote> -<p> -Here's a common example: We have many ISV customers who have built lots of -in-house STL-like containers. Imagine that, for the past ten years, the user -has been happily using his <tt>XYZCorpContainer<T></tt> that has <tt>begin()</tt> and <tt>end()</tt> -and an iterator typedef, and indeed satisfies nearly all of <tt>Container</tt>, -though maybe not quite all just like <tt>valarray</tt>. The user upgrades to a -range-enabled version of a library, and now <tt>lib_algo( xyz.begin(), xyz.end());</tt> -no longer works -- compiler error. -</p> -<p> -Even though <tt>XYZCorpContainer</tt> matches the pre-conceptized version of the -algorithm, and has been working for years, it appears the user has to write -at least this: -</p> -<blockquote><pre> -template<class T> concept_map Range<XYZCorpContainer<T>> {}; - -template<class T> concept_map Range<const XYZCorpContainer<T>> {}; -</pre></blockquote> -<p> -Is that correct? -</p> -<p> -But he may actually have to write this as we do for initializer list: -</p> -<blockquote><pre> -template<class T> -concept_map Range<XYZCorpContainer<T>> { - typedef T* iterator; - iterator begin(XYZCorpContainer<T> c) { return c.begin(); } - iterator end(XYZCorpContainer<T> c) { return c.end(); } -}; - -template<class T> -concept_map Range<const XYZCorpContainer<T>> { - typedef T* iterator; - iterator begin(XYZCorpContainer<T> c) { return c.begin(); } - iterator end(XYZCorpContainer<T> c) { return c.end(); } -}; -</pre></blockquote> - -</blockquote> - -<p><i>[ -2009-04-28 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -I recommend NAD, although remain concerned about header organisation. -</p> -<p> -A user container will satisfy the <tt>MemberContainer</tt> concept, which IS auto. -There is a concept_map for all <tt>MemberContainers</tt> to <tt>Container</tt>, and then a -further concept_map for all <tt>Container</tt> to <tt>Range</tt>, so the stated problem is not -actually true. User defined containers will automatically match the <tt>Range</tt> -concept without explicitly declaring a concept_map. -</p> -<p> -The problem is that they should now provide an additional two headers, -<tt><iterator_concepts></tt> and <tt><container_concepts></tt>. - The only difference from -making <tt>Range</tt> an auto concept would be this reduces to a single header, -<tt><iterator_concepts></tt>. -</p> -<p> -I am strongly in favour of any resolution that tackles the issue of -explicitly requiring concept headers to make these concept maps available. -</p> -</blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We observe there is a recent paper by Bjarne that overlaps this issue. -</p> -<p> -Alisdair continues to recommend NAD. -</p> -<p> -Move to Open, and recommend the issue be deferred until after the next -Committee Draft is issued. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1107"></a>1107. constructor <tt>shared_future(unique_future)</tt> by value?</h3> -<p><b>Section:</b> 30.6.7 [futures.shared_future] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Thomas J. Gritzan <b>Opened:</b> 2009-04-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.shared_future">issues</a> in [futures.shared_future].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In the <tt>shared_future</tt> class definition in 30.6.7 [futures.shared_future] -the move constructor -that constructs a <tt>shared_future</tt> from an <tt>unique_future</tt> receives the -parameter by value. In paragraph 3, the same constructor receives it as -const value. -</p> - -<p> -I think that is a mistake and the constructor should take a r-value -reference: -</p> - -<blockquote><pre> -shared_future(unique_future<R>&& rhs); -</pre></blockquote> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree with the proposed resolution. -<p/> -Move to Tentatively Ready. -</p> -</blockquote> - -<p><i>[ -2009-07-05 Daniel notes: -]</i></p> - - -<blockquote><p> -The proposed change has already been incorported into the current working draft -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2914.pdf">N2914</a>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change the synopsis in 30.6.7 [futures.shared_future]: -</p> - -<blockquote><pre> -shared_future(unique_future<R><ins>&&</ins> rhs); -</pre></blockquote> - -<p> -Change the definition of the constructor in 30.6.7 [futures.shared_future]: -</p> - -<blockquote><pre> -shared_future(<del>const</del> unique_future<R><ins>&&</ins> rhs); -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1109"></a>1109. <tt>std::includes</tt> should require <tt>CopyConstructible</tt> predicate</h3> -<p><b>Section:</b> 25.4.5.1 [includes] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-04-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#includes">issues</a> in [includes].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -All the set operation algorithms require a <tt>CopyConstructible</tt> predicate, with -the exception of <tt>std::includes</tt>. This looks like a typo as much as anything, -given the general library requirement that predicates are copy -constructible, and wording style of other set-like operations. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote><p> -We agree with the proposed resolution. -Move to NAD Editorial. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Change [algorithms.syn] and 25.4.5.1 [includes]: -</p> - -<blockquote><pre> -template<InputIterator Iter1, InputIterator Iter2, - <del>typename</del> <ins>CopyConstructible</ins> Compare> - requires Predicate<Compare, Iter1::value_type, Iter2::value_type> - && Predicate<Compare, Iter2::value_type, Iter1::value_type> - bool includes(Iter1 first1, Iter1 last1, - Iter2 first2, Iter2 last2, - Compare comp); -</pre></blockquote> - - - - - -<hr> -<h3><a name="1111"></a>1111. associative containers underconstrained</h3> -<p><b>Section:</b> 23.4 [associative] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-04-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative">active issues</a> in [associative].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative">issues</a> in [associative].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -According to table 87 (n2857) the expression <tt>X::key_equal</tt> for an unordered -container shall return a value of type <tt>Pred</tt>, where <tt>Pred</tt> is an equivalence -relation. -</p> - -<p> -However, all 4 containers constrain <tt>Pred</tt> to be merely a <tt>Predicate</tt>, -and not <tt>EquivalenceRelation</tt>. -</p> - -<p><i>[ -Batavia (2009-05): -]</i></p> - -<blockquote> -<p> -We agree with the proposed resolution. -</p> -<p> -Move to Review. -</p> -</blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -For ordered containers, replace -</p> -<blockquote><pre> -Predicate<auto, Key, Key> Compare = less<Key> -</pre></blockquote> -<p> -with -</p> -<blockquote><pre> -StrictWeakOrder<auto, Key, Key> Compare = less<Key> -</pre></blockquote> - -<p> -For unordered containers, replace -</p> -<blockquote><pre> -Predicate<auto, Key, Key> Compare = less<Key> -</pre></blockquote> -<p> -with -</p> -<blockquote><pre> -EquivalenceRelation<auto, Key, Key> Compare = less<Key> -</pre></blockquote> -<p> -As in the following declarations: -</p> - -<blockquote> -<p> -Associative containers 23.4 [associative] -</p> -<p> - 1 Headers <tt><map></tt> and <tt><set></tt>: -</p> -<p> - Header <tt><map></tt> synopsis -</p> -<blockquote><pre> - namespace std { - template <ValueType Key, ValueType T, - <del>Predicate</del><ins>StrictWeakOrder</ins><auto, Key<del>, Key</del>> Compare = less<Key>, - Allocator Alloc = allocator<pair<const Key, T> > > - requires NothrowDestructible<Key> && NothrowDestructible<T> - && CopyConstructible<Compare> - && AllocatableElement<Alloc, Compare, const Compare&> - && AllocatableElement<Alloc, Compare, Compare&&> - class map; - - ... - - template <ValueType Key, ValueType T, - <del>Predicate</del><ins>StrictWeakOrder</ins><auto, Key<del>, Key</del>> Compare = less<Key>, - Allocator Alloc = allocator<pair<const Key, T> > > - requires NothrowDestructible<Key> && NothrowDestructible<T> - && CopyConstructible<Compare> - && AllocatableElement<Alloc, Compare, const Compare&> - && AllocatableElement<Alloc, Compare, Compare&&> - class multimap; - - ... - - } -</pre></blockquote> - -<p> - Header <set> synopsis -</p> -<blockquote><pre> - namespace std { - template <ValueType Key, <del>Predicate</del><ins>StrictWeakOrder</ins><auto, Key<del>, Key</del>> Compare = less<Key>, - Allocator Alloc = allocator<Key> > - requires NothrowDestructible<Key> && CopyConstructible<Compare> - && AllocatableElement<Alloc, Compare, const Compare&> - && AllocatableElement<Alloc, Compare, Compare&&> - class set; - - ... - - template <ValueType Key, <del>Predicate</del><ins>StrictWeakOrder</ins><auto, Key<del>, Key</del>> Compare = less<Key>, - Allocator Alloc = allocator<Key> > - requires NothrowDestructible<Key> && CopyConstructible<Compare> - && AllocatableElement<Alloc, Compare, const Compare&> - && AllocatableElement<Alloc, Compare, Compare&&> - class multiset; - - ... - - } -</pre></blockquote> - -<p> - 23.4.1p2 Class template map [map] -</p> -<blockquote><pre> - namespace std { - template <ValueType Key, ValueType T, - <del>Predicate</del><ins>StrictWeakOrder</ins><auto, Key<del>, Key</del>> Compare = less<Key>, - Allocator Alloc = allocator<pair<const Key, T> > > - requires NothrowDestructible<Key> && NothrowDestructible<T> - && CopyConstructible<Compare> - && AllocatableElement<Alloc, Compare, const Compare&> - && AllocatableElement<Alloc, Compare, Compare&&> - class map { - ... - }; - } -</pre></blockquote> - - -<p> - 23.4.2p2 Class template multimap [multimap] -</p> -<blockquote><pre> - namespace std { - template <ValueType Key, ValueType T, - <del>Predicate</del><ins>StrictWeakOrder</ins><auto, Key<del>, Key</del>> Compare = less<Key>, - Allocator Alloc = allocator<pair<const Key, T> > > - requires NothrowDestructible<Key> && NothrowDestructible<T> - && CopyConstructible<Compare> - && AllocatableElement<Alloc, Compare, const Compare&> - && AllocatableElement<Alloc, Compare, Compare&&> - class multimap { - ... - }; - } -</pre></blockquote> - - -<p> - 23.4.3p2 Class template set [set] -</p> -<blockquote><pre> - namespace std { - template <ValueType Key, <del>Predicate</del><ins>StrictWeakOrder</ins><auto, Key<del>, Key</del>> Compare = less<Key>, - Allocator Alloc = allocator<Key> > - requires NothrowDestructible<Key> && CopyConstructible<Compare> - && AllocatableElement<Alloc, Compare, const Compare&> - && AllocatableElement<Alloc, Compare, Compare&&> - class set { - ... - }; - } -</pre></blockquote> - - -<p> - 23.4.4p2 Class template multiset [multiset] -</p> -<blockquote><pre> - namespace std { - template <ValueType Key, <del>Predicate</del><ins>StrictWeakOrder</ins><auto, Key<del>, Key</del>> Compare = less<Key>, - Allocator Alloc = allocator<Key> > - requires NothrowDestructible<Key> && CopyConstructible<Compare> - && AllocatableElement<Alloc, Compare, const Compare&> - && AllocatableElement<Alloc, Compare, Compare&&> - class multiset { - ... - }; - } -</pre></blockquote> - -<p> - 23.5 Unordered associative containers [unord] -</p> -<p> - 1 Headers <unordered_map> and <unordered_set>: -</p> -<p> - Header <unordered_map> synopsis -</p> -<blockquote><pre> - namespace std { - // 23.5.1, class template unordered_map: - template <ValueType Key, - ValueType T, - Callable<auto, const Key&> Hash = hash<Key>, - <del>Predicate</del><ins>EquivalenceRelation</ins><auto, Key<del>, Key</del>> Pred = equal_to<Key>, - Allocator Alloc = allocator<pair<const Key, T> > > - requires NothrowDestructible<Key> && NothrowDestructible<T> - && SameType<Hash::result_type, size_t> - && CopyConstructible<Hash> && CopyConstructible<Pred> - && AllocatableElement<Alloc, Pred, const Pred&> - && AllocatableElement<Alloc, Pred, Pred&&> - && AllocatableElement<Alloc, Hash, const Hash&> - && AllocatableElement<Alloc, Hash, Hash&&> - class unordered_map; - - // 23.5.2, class template unordered_multimap: - template <ValueType Key, - ValueType T, - Callable<auto, const Key&> Hash = hash<Key>, - <del>Predicate</del><ins>EquivalenceRelation</ins><auto, Key<del>, Key</del>> Pred = equal_to<Key>, - Allocator Alloc = allocator<pair<const Key, T> > > - requires NothrowDestructible<Key> && NothrowDestructible<T> - && SameType<Hash::result_type, size_t> - && CopyConstructible<Hash> && CopyConstructible<Pred> - && AllocatableElement<Alloc, Pred, const Pred&> - && AllocatableElement<Alloc, Pred, Pred&&> - && AllocatableElement<Alloc, Hash, const Hash&> - && AllocatableElement<Alloc, Hash, Hash&&> - class unordered_multimap; - - ... - } -</pre></blockquote> - -<p> - Header <unordered_set> synopsis -</p> -<blockquote><pre> - namespace std { - // 23.5.3, class template unordered_set: - template <ValueType Value, - Callable<auto, const Value&> Hash = hash<Value>, - <del>Predicate</del><ins>EquivalenceRelation</ins><auto, Value<del>, Value</del>> class Pred = equal_to<Value>, - Allocator Alloc = allocator<Value> > - requires NothrowDestructible<Value> - && SameType<Hash::result_type, size_t> - && CopyConstructible<Hash> && CopyConstructible<Pred> - && AllocatableElement<Alloc, Pred, const Pred&> - && AllocatableElement<Alloc, Pred, Pred&&> - && AllocatableElement<Alloc, Hash, const Hash&> - && AllocatableElement<Alloc, Hash, Hash&&> - class unordered_set; - - // 23.5.4, class template unordered_multiset: - template <ValueType Value, - Callable<auto, const Value&> Hash = hash<Value>, - <del>Predicate</del><ins>EquivalenceRelation</ins><auto, Value<del>, Value</del>> class Pred = equal_to<Value>, - Allocator Alloc = allocator<Value> > - requires NothrowDestructible<Value> - && SameType<Hash::result_type, size_t> - && CopyConstructible<Hash> && CopyConstructible<Pred> - && AllocatableElement<Alloc, Pred, const Pred&> - && AllocatableElement<Alloc, Pred, Pred&&> - && AllocatableElement<Alloc, Hash, const Hash&> - && AllocatableElement<Alloc, Hash, Hash&&> - class unordered_multiset; - - ... - } -</pre></blockquote> - -<p> - 23.5.1p3 Class template unordered_map [unord.map] -</p> -<blockquote><pre> - namespace std { - template <ValueType Key, - ValueType T, - Callable<auto, const Key&> Hash = hash<Key>, - <del>Predicate</del><ins>EquivalenceRelation</ins><auto, Key<del>, Key</del>> Pred = equal_to<Key>, - Allocator Alloc = allocator<pair<const Key, T> > > - requires NothrowDestructible<Key> && NothrowDestructible<T> - && SameType<Hash::result_type, size_t> - && CopyConstructible<Hash> && CopyConstructible<Pred> - && AllocatableElement<Alloc, Pred, const Pred&> - && AllocatableElement<Alloc, Pred, Pred&&> - && AllocatableElement<Alloc, Hash, const Hash&> - && AllocatableElement<Alloc, Hash, Hash&&> - class unordered_map - { - ... - }; - } -</pre></blockquote> - -<p> - 23.5.2p3 Class template unordered_multimap [unord.multimap] -</p> -<blockquote><pre> - namespace std { - template <ValueType Key, - ValueType T, - Callable<auto, const Key&> Hash = hash<Key>, - <del>Predicate</del><ins>EquivalenceRelation</ins><auto, Key<del>, Key</del>> Pred = equal_to<Key>, - Allocator Alloc = allocator<pair<const Key, T> > > - requires NothrowDestructible<Key> && NothrowDestructible<T> - && SameType<Hash::result_type, size_t> - && CopyConstructible<Hash> && CopyConstructible<Pred> - && AllocatableElement<Alloc, Pred, const Pred&> - && AllocatableElement<Alloc, Pred, Pred&&> - && AllocatableElement<Alloc, Hash, const Hash&> - && AllocatableElement<Alloc, Hash, Hash&&> - class unordered_multimap - { - ... - }; - } -</pre></blockquote> - -<p> - 23.5.3p3 Class template unordered_set [unord.set] -</p> -<blockquote><pre> - namespace std { - template <ValueType Value, - Callable<auto, const Value&> Hash = hash<Value>, - <del>Predicate</del><ins>EquivalenceRelation</ins><auto, Value<del>, Value</del>> class Pred = equal_to<Value>, - Allocator Alloc = allocator<Value> > - requires NothrowDestructible<Value> - && SameType<Hash::result_type, size_t> - && CopyConstructible<Hash> && CopyConstructible<Pred> - && AllocatableElement<Alloc, Pred, const Pred&> - && AllocatableElement<Alloc, Pred, Pred&&> - && AllocatableElement<Alloc, Hash, const Hash&> - && AllocatableElement<Alloc, Hash, Hash&&> - class unordered_set - { - ... - }; - } -</pre></blockquote> -<p> - 23.5.4p3 Class template unordered_multiset [unord.multiset] -</p> -<blockquote><pre> - namespace std { - template <ValueType Value, - Callable<auto, const Value&> Hash = hash<Value>, - <del>Predicate</del><ins>EquivalenceRelation</ins><auto, Value<del>, Value</del>> class Pred = equal_to<Value>, - Allocator Alloc = allocator<Value> > - requires NothrowDestructible<Value> - && SameType<Hash::result_type, size_t> - && CopyConstructible<Hash> && CopyConstructible<Pred> - && AllocatableElement<Alloc, Pred, const Pred&> - && AllocatableElement<Alloc, Pred, Pred&&> - && AllocatableElement<Alloc, Hash, const Hash&> - && AllocatableElement<Alloc, Hash, Hash&&> - class unordered_multiset - { - ... - }; - } -</pre></blockquote> - -</blockquote> - - - - - - -<hr> -<h3><a name="1115"></a>1115. <tt>va_copy</tt> missing from Standard macros table</h3> -<p><b>Section:</b> C.5 [diff.library] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Miles Zhao <b>Opened:</b> 2009-05-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#diff.library">issues</a> in [diff.library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In "Table 122 — Standard macros" of C.5 [diff.library], which lists the 56 macros -inherited from C library, <tt>va_copy</tt> seems to be missing. But in -"Table 21 — Header <tt><cstdarg></tt> synopsis" (18.10 [support.runtime]), there is. -</p> - -<p><i>[ -2009-10 post-Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as Tentatively NAD Editorial, if Pete disagrees, Howard -will move to Tentatively Ready -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add <tt>va_copy</tt> to Table 122 -- Standard macros in C.5 [diff.library]. -</p> - - - - - -<hr> -<h3><a name="1119"></a>1119. tuple query APIs do not support references</h3> -<p><b>Section:</b> 20.4.2.5 [tuple.helper] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-05-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#tuple.helper">issues</a> in [tuple.helper].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The <tt>tuple</tt> query APIs <tt>tuple_size</tt> and -<tt>tuple_element</tt> do not support references-to-tuples. This can be -annoying when a template deduced a parameter type to be a reference, -which must be explicitly stripped with <tt>remove_reference</tt> before calling -these APIs. -</p> -<p> -I am not proposing a resolution at this point, as there is a -combinatorial explosion with lvalue/rvalue references and -cv-qualification (see previous issue) that suggests some higher -refactoring is in order. This might be something to kick back over to -Core/Evolution. -</p> -<p> -Note that we have the same problem in numeric_limits. -</p> - -<p><i>[ -2009-10 post-Santa Cruz: -]</i></p> - - -<blockquote><p> -Move to Open. Alisdair to provide wording. -</p></blockquote> - - -<p><i>[ -2010 Rapperswil: -]</i></p> - - -<blockquote><p> -Move to NAD. This is an extension after the FCD, without a clear motivation. -May consider as NAD Future if motivating examples come forward. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1124"></a>1124. Invalid definition of concept RvalueOf</h3> -<p><b>Section:</b> X [concept.transform] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2009-05-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#concept.transform">issues</a> in [concept.transform].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -A recent news group -<a href="http://groups.google.de/group/comp.std.c++/browse_frm/thread/8eb92768a19fb46f">article</a> -points to several defects in the -specification of reference-related concepts. -</p> -<p> -One problem of the concept <tt>RvalueOf</tt> as currently defined in -X [concept.transform]: -</p> - -<blockquote><pre> -concept RvalueOf<typename T> { - typename type = T&&; - requires ExplicitlyConvertible<T&,type> && Convertible<T&&,type>; -} - -template<typename T> concept_map RvalueOf<T&> { - typedef T&& type; -} -</pre></blockquote> - -<p> -is that if <tt>T</tt> is an lvalue-reference, the requirement -<tt>Convertible<T&&,type></tt> isn't satisfied for -lvalue-references, because after reference-collapsing in the concept -definition we have <tt>Convertible<T&,type></tt> in this case, -which isn't satisfied in the concept map template and also is not the -right constraint either. I think that the reporter is right that -<tt>SameType</tt> requirements should do the job and that we also should -use the new <tt>RvalueReference</tt> concept to specify a best matching -type requirement. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In X [concept.transform] before p. 4 change as indicated: -</p> - -<blockquote><pre> -auto concept RvalueOf<typename T> { - <del>typename</del><ins>RvalueReference</ins> type = T&&; - requires <del>ExplicitlyConvertible<T&, type> && Convertible<T&&, type></del><ins>SameType<T&, type&></ins>; -} -</pre></blockquote> - - - - - -<hr> -<h3><a name="1125"></a>1125. ostream_iterator does not work with movable types</h3> -<p><b>Section:</b> 24.6.2.2 [ostream.iterator.ops] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-05-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -<tt>ostream_iterator</tt> has not been updated to support moveable types, in a -similar manner to the insert iterators. -Note that this is not a problem for <tt>ostreambuf_iterator</tt>, as the types it is -restricted to dealing with do not support extra-efficient moving. -</p> - -<p><i>[ -2009-11-10 Howard adds: -]</i></p> - - -<blockquote><p> -Moved to Tentatively NAD after 5 positive votes on c++std-lib. Rationale -added below. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Add second <tt>operator=</tt> overload to class <tt>template ostream_iterator</tt> -in 24.6.2 [ostream.iterator], para 2: -</p> - -<blockquote><pre> -ostream_iterator<T,charT,traits>& operator=(const T& value); -<ins>ostream_iterator<T,charT,traits>& operator=(T&& value);</ins> -</pre></blockquote> - -<p> -Add a new paragraph: in 24.6.2.2 [ostream.iterator.ops]: -</p> - -<blockquote> -<pre> -ostream_iterator& operator=(T&& value); -</pre> -<blockquote> -<p> --2- <i>Effects:</i> -</p> -<blockquote><pre> -*out_stream << std::move(value); -if(delim != 0) - *out_stream << delim; -return (*this); -</pre></blockquote> -</blockquote> -</blockquote> - - - -<p><b>Rationale:</b></p> -<p> -Several objections to move forward with this issue were voiced in the thread -starting with c++std-lib-25438. Among them is that we know of no motivating -use case to make streaming rvalues behave differently than streaming const -lvalues. -</p> - - - - - -<hr> -<h3><a name="1127"></a>1127. rvalue references and iterator traits</h3> -<p><b>Section:</b> 24.4.1 [iterator.traits] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-05-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iterator.traits">issues</a> in [iterator.traits].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The deprecated support for <tt>iterator_traits</tt> and legacy (unconstrained) -iterators features the (exposition only) concept: -</p> - -<blockquote><pre> -concept IsReference<typename T> { } // exposition only -template<typename T> concept_map IsReference<T&> { } -</pre></blockquote> -<p> -Now this looks exactly like the <tt>LvalueReference</tt> concept recently added to -clause 20, so I wonder if we should use that instead? -Then I consider the lack of rvalue-reference support, which means that -<tt>move_iterator</tt> would always flag as merely supporting the <tt>input_iterator_tag</tt> -category. This suggests we retain the exposition concept, but add a second -concept_map to support rvalue references. -</p> -<p> -I would suggest adding the extra concept_map is the right way forward, but -still wonder if the two exposition-only concepts in this clause might be -worth promoting to clause 20. That question might better be answered with a -fuller investigation of type_trait/concept unification though. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In Iterator traits 24.4.1 [iterator.traits] para 4 add: -</p> - -<blockquote><pre> -concept IsReference<typename T> { } // exposition only -template<typename T> concept_map IsReference<T&> { } -<ins>template<typename T> concept_map IsReference<T&&> { }</ins> -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1128"></a>1128. Missing definition of <tt>iterator_traits<T*></tt></h3> -<p><b>Section:</b> X [iterator.syn] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-05-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The <tt><iterator></tt> header synopsis declares a partial specialization of -<tt>iterator_traits</tt> to support pointers, X [iterator.syn]. The implication -is that specialization will be described in D10, yet it did not follow the -rest of the deprecated material into this clause. -</p> -<p> -However, this is not as bad as it first seems! -There are partial specializations of <tt>iterator_traits</tt> for types that satisfy -the various Iterator concepts, and there are concept_maps for pointers to -explicitly support the <tt>RandomAccessIterator</tt> concept, so the required -template will be present - just not in the manner advertised. -</p> -<p> -I can see two obvious solutions: -</p> - -<ol style="list-style-type:lower-roman"> -<li> -Restore the <tt>iterator_traits<T*></tt> partial specialization in D.10 -</li> -<li> -Remove the declaration of <tt>iterator_traits<T*></tt> from 24.3 synopsis -</li> -</ol> -<p> -I recommend option (ii) in the wording below -</p> -<p> -Option (ii) could be extended to strike all the declarations of deprecated -material from the synopsis, as it is effectively duplicating D.10 anyway. -This is the approach taken for deprecated library components in the 98/03 -standards. This is probably a matter best left to the Editor though. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In X [iterator.syn] strike: -</p> - -<blockquote><pre> -<del>template<class T> struct iterator_traits<T*>;</del> -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1132"></a>1132. JP-30: nested exceptions</h3> -<p><b>Section:</b> 18.8.6 [except.nested] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Seiji Hayashida <b>Opened:</b> 2009-06-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#except.nested">active issues</a> in [except.nested].</p> -<p><b>View all other</b> <a href="lwg-index.html#except.nested">issues</a> in [except.nested].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses JP 30</b></p> - -<p> -C++0x <tt>nested_exception</tt> cannot handle a structured exception well. The -following codes show two types of tree structured exception handling. -</p> -<p> -The first one is based on <tt>nested_exception</tt> in C++0x, -while the second one is based on my library <tt>trickerr.h</tt> (in Japanese). -<a href="http://tricklib.com/cxx/dagger/trickerr.h">http://tricklib.com/cxx/dagger/trickerr.h</a> -</p> -<p> -Assume that Function <tt>A()</tt> calls two sub functions <tt>A_a()</tt> and <tt>A_b()</tt>, both might -throw tree structured exceptions, and <tt>A_b()</tt> must be called even if <tt>A_a()</tt> -throws an exception. -</p> -<p> -List A (code of tree structured exception handling based on nested_exception -in C++0x) -</p> - -<blockquote><pre> -void A() -{ - try - { - std::vector<exception_ptr> exception_list; - try - { - // A_a() does a similar processing as A(). - A_a(); - } - catch(...) - { - exception_list.push_back(current_exception()); - } - - // ***The processing A() has to do even when A_a() fails. *** - try - { - // A_b() does a similar processing as A(). - A_b(); - } - catch(...) - { - exception_list.push_back(current_exception()); - } - if (!exception_list.empty()) - { - throw exception_list; - } - } - catch(...) - { - throw_with_nested(A_exception("someone error")); - } -} -void print_tree_exception(exception_ptr e, const std::string & indent ="") -{ - const char * indent_unit = " "; - const char * mark = "- "; - try - { - rethow_exception(e); - } - catch(const std::vector<exception_ptr> e) - { - for(std::vector<exception_ptr>::const_iterator i = e.begin(); i!=e.end(); ++i) - { - print_tree_exception(i, indent); - } - } - catch(const std::nested_exception e) - { - print_tree_exception(evil_i(e), indent +indent_unit); - } - catch(const std::exception e) - { - std::cout << indent << mark << e.what() << std::endl; - } - catch(...) - { - std::cout << indent << mark << "unknown exception" << std::endl; - } -} -int main(int, char * []) -{ - try - { - A(); - } - catch() - { - print_tree_exception(current_exception()); - } - return EXIT_SUCCESS; -} -</pre></blockquote> - -<p> -List B ( code of tree structured exception handling based on <tt>trickerr.h</tt>. ) -"trickerr.h" (in Japanese), refer to: -<a href="http://tricklib.com/cxx/dagger/trickerr.h">http://tricklib.com/cxx/dagger/trickerr.h</a>. -</p> - -<blockquote><pre> -void A() -{ - tricklib::error_listener_type error_listener; - // A_a() is like A(). A_a() can throw tree structured exception. - A_a(); - - // *** It must do process so that A_a() throws exception in A(). *** - // A_b() is like A(). A_b() can throw tree structured exception. - A_b(); - - if (error_listener.has_error()) // You can write this "if block" in destructor - // of class derived from error_listener_type. - { - throw_error(new A_error("someone error",error_listener.listener_off().extract_pending_error())); - } -} -void print_tree_error(const tricklib::error_type &a_error, const std::string & indent = "") -{ - const char * indent_unit = " "; - const char * mark = "- "; - - tricklib::error_type error = a_error; - while(error) - { - std::cout << indent << mark << error->message << std::endl; - if (error->children) - { - print_tree_error(error->children, indent +indent_unit); - } - error = error->next; - } -} -int main(int, char * []) -{ - tricklib::error_thread_power error_thread_power_on; // This object is necessary per thread. - - try - { - A(); - } - catch(error_type error) - { - print_tree_error(error); - } - catch(...) - { - std::cout << "- unknown exception" << std::endl; - } - return EXIT_SUCCESS; -} -</pre></blockquote> - -<p> -Prospect -</p> -<p> -We will focus on the method A() since the other methods, also main(), occur -only once respectively. -</p> - -<ul> -<li> - In the List A above (of the nested exception handling), it is hard to - find out an active reason to use the nested exception handling at this - scene. Rather, we can take a simpler description by throwing the entire - exception_list directly to the top level. -</li> -<li> - The code in the same example gives us a kind of redundant impression, - which might have come from the fact that the try-throw-catch framework does - not assume a tree structured exception handling. -</li> -</ul> - -<p> -According to the above observation, we cannot help concluding that it is not -so easy to use the nested_exception handling as a tree structured exception -handling mechanism in a practical sense. -</p> -<p> -This text is based on the web page below (in Japanese). -<a href="http://d.hatena.ne.jp/wraith13/20081231/1230715424">http://d.hatena.ne.jp/wraith13/20081231/1230715424</a> -</p> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD. The committee agrees that <tt>nested_exception</tt> is not a good -match for this usage model. The committee did not see a way of improving -this within the timeframe allowed. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="1139"></a>1139. Thread support library not concept enabled</h3> -<p><b>Section:</b> 30 [thread] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> LWG <b>Opened:</b> 2009-06-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread">issues</a> in [thread].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US 93, JP 79, UK 333, JP 81</b></p> - -<p> -The thread chapter is not concept enabled. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1140"></a>1140. Numerics library not concept enabled</h3> -<p><b>Section:</b> 26 [numerics] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> LWG <b>Opened:</b> 2009-06-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#numerics">issues</a> in [numerics].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US 84</b></p> - -<p> -The numerics chapter is not concept enabled. -</p> - -<p> -The portion of this comment dealing with random numbers was resolved by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2836.pdf">N2836</a>, -which was accepted in Summit. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1141"></a>1141. Input/Output library not concept enabled</h3> -<p><b>Section:</b> 27 [input.output] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> LWG <b>Opened:</b> 2009-06-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#input.output">issues</a> in [input.output].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US 85, JP 67, JP 68, JP 69, JP 72, UK 308</b></p> - -<p> -The input/output chapter is not concept enabled. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1142"></a>1142. Regular expressions library not concept enabled</h3> -<p><b>Section:</b> 28 [re] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> LWG <b>Opened:</b> 2009-06-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#re">active issues</a> in [re].</p> -<p><b>View all other</b> <a href="lwg-index.html#re">issues</a> in [re].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US 86, UK 309, UK 310</b></p> - -<p> -The regular expressions chapter is not concept enabled. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1148"></a>1148. Wrong argument type of I/O stream manipulators <tt>setprecision()</tt> -and <tt>setw()</tt></h3> -<p><b>Section:</b> 27.7 [iostream.format] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Marc Steinbach <b>Opened:</b> 2009-06-20 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iostream.format">issues</a> in [iostream.format].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The header <tt><iomanip></tt> synopsis in 27.7 [iostream.format] specifies -</p> -<blockquote><pre> -T5 setprecision(int n); -T6 setw(int n); -</pre></blockquote> - -<p> -The argument types should be streamsize, as in class <tt>ios_base</tt> -(see 27.5.3 [ios.base]): -</p> -<blockquote><pre> -streamsize precision() const; -streamsize precision(streamsize prec); -streamsize width() const; -streamsize width(streamsize wide); -</pre></blockquote> - -<p> -(Editorial: 'wide' should probably be renamed as 'width', or maybe just 'w'.) -</p> - -<p><i>[ -2009-07-29 Daniel clarified wording. -]</i></p> - - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote> -<p> -No concensus for this change. There was some interest in doing the opposite -fix: Change the <tt>streamsize</tt> in <tt><ios></tt> to <tt>int</tt>. -But ultimately there was no concensus for that change either. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -<p> -In 27.7 [iostream.format], header <tt><iomanip></tt> synopsis change as indicated: -</p> - -<blockquote><pre> -T5 setprecision(<del>int</del><ins>streamsize</ins> n); -T6 setw(<del>int</del><ins>streamsize</ins> n); -</pre></blockquote> -</li> - -<li> -<p> -In 27.7.4 [std.manip], just before p. 6 change as indicated: -</p> - -<blockquote><pre> -unspecified setprecision(<del>int</del><ins>streamsize</ins> n); -</pre></blockquote> -</li> - -<li> -<p> -In 27.7.4 [std.manip], just before p. 7 change as indicated: -</p> - -<blockquote><pre> -unspecified setw(<del>int</del><ins>streamsize</ins> n); -</pre></blockquote> -</li> -</ol> - - - - - - - - -<hr> -<h3><a name="1149"></a>1149. Reformulating NonemptyRange axiom</h3> -<p><b>Section:</b> X [rand.concept.urng] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Walter Brown <b>Opened:</b> 2009-06-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In X [rand.concept.urng], we have the following: -</p> -<blockquote><pre> -concept UniformRandomNumberGenerator<typename G> : Callable<G> { - ... - axiom NonemptyRange(G& g) { - G::min() < G::max(); - } - ... -} -</pre></blockquote> - -<p> -Since the parameter <tt>G</tt> is in scope throughout the concept, there is no -need for the axiom to be further parameterized, and so the axiom can be -slightly simplified as: -</p> - -<blockquote><pre> -axiom NonemptyRange() { - G::min() < G::max(); -} -</pre></blockquote> - -<p> -We can further reformulate so as to avoid any axiom machinery as: -</p> - -<blockquote><pre> -requires True< G::min() < G::max() >; -</pre></blockquote> - -<p> -This is not only a simpler statement of the same requirement, but also -forces the requirement to be checked. -</p> - -<p><i>[ -Post-Rapperswil: -]</i></p> - - -<blockquote><p> -Moved to Tentatively Ready after 5 positive votes on c++std-lib. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -In X [rand.concept.urng], replace the <tt>NonemptyRange</tt> axiom by: -</p> - -<blockquote><pre> -<del>axiom NonemptyRange(G& g) { - G::min() < G::max(); -}</del> -<ins>requires True< G::min() < G::max() >;</ins> -</pre></blockquote> - - - - - - -<hr> -<h3><a name="1153"></a>1153. Standard library needs review for constructors to be -explicit to avoid treatment as initializer-list constructor</h3> -<p><b>Section:</b> 17 [library], 30 [thread], D [depr] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> LWG <b>Opened:</b> 2009-06-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses DE 2</b></p> - -<p><b>Description</b></p> - <p>Marking a constructor with <tt>explicit</tt> has semantics - even for a constructor with zero or several parameters: - Such a constructor cannot be used with list-initialization - in a copy-initialization context, see 13.3.1.7 [over.match.list]. The - standard library apparently has not been reviewed for - marking non-single-parameter constructors as <tt>explicit</tt>.</p> -<p><b>Suggestion</b></p> - <p>Consider marking zero-parameter and multi-parameter - constructors <tt>explicit</tt> in classes that have at least one - constructor marked <tt>explicit</tt> and that do not have an - initializer-list constructor.</p> - -<p><b>Notes</b></p> - <p>Robert Klarer to address this one.</p> - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote><p> -Move to "Open". Robert Klarer has promised to provide wording. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: Moved to NAD, rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -We are unaware of any cases where initializer lists cause problem in this -context, but if problems arise in the future the issue can be reopened. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1155"></a>1155. Reference should be to C99</h3> -<p><b>Section:</b> C.5 [diff.library] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> LWG <b>Opened:</b> 2009-06-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#diff.library">issues</a> in [diff.library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses FR 38</b></p> - -<p><b>Description</b></p> - <p>What is ISO/IEC 1990:9899/DAM - 1? My guess is that's a typo for ISO/IEC - 9899/Amd.1:1995 which I'd - have expected to be referenced here (the tables - make reference to things - which were introduced by Amd.1).</p> -<p><b>Suggestion</b></p> - <p>One need probably a reference - to the document which introduce <tt>char16_t</tt> and - <tt>char32_t</tt> in C (ISO/IEC TR 19769:2004?).</p> -<p><b>Notes</b></p> -<p>Create issue. Document in question should be C99, not C90+amendment1. The - rest of the section requires careful review for completeness. Example <cstdint> - 18.4.1 [cstdint.syn]. Assign to C liasons.</p> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -NAD Editorial. Already fixed. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1156"></a>1156. Constraints on bitmask and enumeration types to be tightened</h3> -<p><b>Section:</b> 17.5.2.1.2 [enumerated.types], 17.5.2.1.3 [bitmask.types] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> LWG <b>Opened:</b> 2009-06-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 165</b></p> - -<p><b>Description</b></p> - <p>Constraints on - bitmask and enumeration types were supposed to be tightened - up as part of the motivation for the <tt>constexpr</tt> feature - - see paper - <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2235.pdf">N2235</a> - for details</p> -<p><b>Suggestion</b></p> - <p>Adopt wording in line with the motivation - described in - <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2235.pdf">N2235</a></p> -<p><b>Notes</b></p> - <p>Robert Klarer to review</p> - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote><p> -Move to Open. Ping Robert Klarer to provide wording, using N2235 as guidance. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: -]</i></p> - - -<blockquote><p> -Moved to NAD. Rationale added. -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p> -UK NB did not sufficiently describe how to resolve their comment, and -therefore we cannot make a change for the FCD. If a resolution were -provided in the future, we would be happy to apply it. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1164"></a>1164. <tt>promise::swap</tt> should pass by rvalue reference</h3> -<p><b>Section:</b> 30.6.5 [futures.promise] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> LWG <b>Opened:</b> 2009-06-28 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#futures.promise">active issues</a> in [futures.promise].</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.promise">issues</a> in [futures.promise].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses UK 341</b></p> - -<p><b>Description</b></p> -<p><tt>promise::swap</tt> accepts its parameter by lvalue reference. This is -inconsistent with other types that provide a swap member function, -where those swap functions accept an rvalue reference</p> - -<p><b>Suggestion</b></p> -<p>Change <tt>promise::swap</tt> to take an rvalue reference.</p> - -<p><b>Notes</b></p> -<p>Create an issue. Detlef will look into it. Probably ready as it.</p> - -<p><i>[ -2009-07 Frankfurt -]</i></p> - - -<blockquote><p> -NAD, by virtue of the changed rvalue rules and swap signatures from Summit. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1167"></a>1167. <tt>pair<T,U></tt> doesn't model <tt>LessThanComparable</tt> in unconstrained code even if - <tt>T</tt> and <tt>U</tt> do.</h3> -<p><b>Section:</b> 20.3 [pairs] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Dave Abrahams <b>Opened:</b> 2009-07-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#pairs">issues</a> in [pairs].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -<tt>LessThanComparable</tt> requires (and provides default - implementations for) <=,>, and >=. However, the defaults - don't take effect in unconstrained code. -</p> -<p> -Still, it's a problem to have types acting one way in -constrained code and another in unconstrained code, except in cases of -syntax adaptation. It's also inconsistent with the containers, which -supply all those operators. -</p> -<p> -Totally Unbiased -Suggested Resolution: -</p> -<p> -accept the exported concept maps proposal and - change the way this stuff is handled to use an - explicit exported concept map rather than nested - function templates -</p> -<p> -e.g., remove from the body of <tt>std::list</tt> -</p> -<blockquote><pre> -template <LessThanComparable T, class Allocator> -bool operator< (const list<T,Allocator>& x, const list<T,Allocator>& y); -template <LessThanComparable T, class Allocator> -bool operator> (const list<T,Allocator>& x, const list<T,Allocator>& y); -template <LessThanComparable T, class Allocator> -bool operator>=(const list<T,Allocator>& x, const list<T,Allocator>& y); -template <LessThanComparable T, class Allocator> -bool operator<=(const list<T,Allocator>& x, const list<T,Allocator>& y); -</pre></blockquote> -<p> -and add this concept_map afterwards: -</p> -<blockquote><pre> -template <LessThanComparable T, class Allocator> -export concept_map LessThanComparable<list<T,Allocator> > -{ - bool operator<(const list<T,Allocator>& x, const list<T,Allocator>& y); -} -</pre></blockquote> -<p> -do similarly for <tt>std::pair</tt>. While you're at it, do the same for -<tt>operator==</tt> and <tt>!=</tt> everywhere, and seek out other such opportunities. -</p> -<p> -Alternative Resolution: keep the ugly, complex specification and add the - missing operators to <tt>std::pair</tt>. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1168"></a>1168. Odd wording for bitset equality operators</h3> -<p><b>Section:</b> 20.6.2 [bitset.members] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-07-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#bitset.members">issues</a> in [bitset.members].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The following wording seems a little unusual to me: -</p> -<p> -p42/43 20.6.2 [bitset.members] -</p> - -<blockquote> -<pre> -bool operator==(const bitset<N>& rhs) const; -</pre> -<blockquote><p> --42- <i>Returns:</i> A nonzero value if the value of each bit in -<tt>*this</tt> equals the value of the corresponding bit in -<tt>rhs</tt>. -</p></blockquote> -<pre> -bool operator!=(const bitset<N>& rhs) const; -</pre> -<blockquote><p> --43- <i>Returns:</i> A nonzero value if <tt>!(*this == rhs)</tt>. -</p></blockquote> -</blockquote> - -<p> -"A nonzero value" may be well defined as equivalent to the literal '<tt>true</tt>' -for Booleans, but the wording is clumsy. I suggest replacing "A nonzero value" -with the literal '<tt>true</tt>' (in appropriate font) in each case. -</p> - -<p><i>[ -2009-07-24 Alisdair recommends NAD Editorial. -]</i></p> - - -<p><i>[ -2009-07-27 Pete adds: -]</i></p> - - -<blockquote><p> -It's obviously editorial. There's no need for further discussion. -</p></blockquote> - -<p><i>[ -2009-07-27 Howard sets to NAD Editorial. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 20.6.2 [bitset.members] p42-43: -</p> - -<blockquote> -<pre> -bool operator==(const bitset<N>& rhs) const; -</pre> -<blockquote><p> --42- <i>Returns:</i> <del>A nonzero value</del> <ins><tt>true</tt></ins> if the value of each bit in -<tt>*this</tt> equals the value of the corresponding bit in -<tt>rhs</tt>. -</p></blockquote> -<pre> -bool operator!=(const bitset<N>& rhs) const; -</pre> -<blockquote><p> --43- <i>Returns:</i> <del>A nonzero value</del> <ins><tt>true</tt></ins> if <tt>!(*this == rhs)</tt>. -</p></blockquote> -</blockquote> - - - - - - -<hr> -<h3><a name="1176"></a>1176. Make <tt>thread</tt> constructor non-variadic</h3> -<p><b>Section:</b> 30.3.1.2 [thread.thread.constr] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-07-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.thread.constr">issues</a> in [thread.thread.constr].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The variadic <tt>thread</tt> constructor is causing controversy, e.g. -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2901.pdf">N2901</a>. -This issue has been created as a placeholder for this course of action. -</p> - -<blockquote><pre> -template <class F<del>, class ...Args</del>> thread(F&& f<del>, Args&&... args</del>); -</pre></blockquote> - -<p> -See <a href="lwg-defects.html#929">929</a> for wording which specifies an rvalue-ref signature but -with "decay behavior", but using variadics. -</p> - -<p><i>[ -2009-11-17 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p> -<p> -The (tentative) concensus of the LWG is to keep the variadic thread constructor. -</p> - - - - - -<hr> -<h3><a name="1179"></a>1179. Probably editorial in [structure.specifications]</h3> -<p><b>Section:</b> 17.5.1.4 [structure.specifications] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Robert Klarer <b>Opened:</b> 2009-07-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#structure.specifications">issues</a> in [structure.specifications].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -While reviewing <a href="lwg-closed.html#971">971</a> I noted that 17.5.1.4 [structure.specifications]/7 says: -</p> - -<blockquote><p> --7- Error conditions specify conditions where a function may fail. The -conditions are listed, together with a suitable explanation, as the <tt>enum -class errc</tt> constants (19.5) that could be used as an argument to -function <tt>make_error_condition</tt> (19.5.3.6). -</p></blockquote> - -<p> -This paragraph should mention <tt>make_error_code</tt> or the text "that -could be used as an argument to function <tt>make_error_condition</tt> -(19.5.3.6)" should be deleted. I believe this is editorial. -</p> - -<p><i>[ -2009-07-21 Chris adds: -]</i></p> - - -<blockquote> -<p> -I'm not convinced there's a problem there, because as far as the "Error -conditions" clauses are concerned, make_error_condition() is used by a -user to test for the condition, whereas make_error_code is not. For -example: -</p> - -<blockquote><pre> -void foobar(error_code& ec = throws()); -</pre></blockquote> - -<p> - Error conditions: -</p> -<blockquote><p> -permission_denied - Insufficient privilege to perform operation. -</p></blockquote> - -<p> -When a user writes: -</p> - -<blockquote><pre> -error_code ec; -foobar(ec); -if (ec == errc::permission_denied) - ... -</pre></blockquote> - -<p> -the implicit conversion <tt>errc->error_condition</tt> makes the if-test -equivalent to: -</p> - -<blockquote><pre> -if (ec == make_error_condition(errc::permission_denied)) -</pre></blockquote> - -<p> -On the other hand, if the user had written: -</p> - -<blockquote><pre> -if (ec == make_error_code(errc::permission_denied)) -</pre></blockquote> - -<p> -the test is now checking for a specific error code. The test may -evaluate to <tt>false</tt> even though <tt>foobar()</tt> failed due to the documented -error condition "Insufficient privilege". -</p> -</blockquote> - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote> -<p> -NAD Editorial. -</p> -<p> -What the WP says right now is literally true: these codes can be used as -an argument to <tt>make_error_condition</tt>. (It is also true that they can be -used as an argument to <tt>make_error_code</tt>, which the WP doesn't say.) Maybe -it would be clearer to just delete "that could be used as an argument to -function <tt>make_error_condition</tt>", since that fact is already implied by -other things that we say. We believe that this is editorial. -</p> -</blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="1186"></a>1186. Forward list could model a stack</h3> -<p><b>Section:</b> 23.6.5 [stack] <b>Status:</b> <a href="lwg-active.html#NAD Concepts">NAD Concepts</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-07-31 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Concepts">NAD Concepts</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The library template <tt>forward_list</tt> could easily model the idea of a -<tt>stack</tt>, where the operations work on the front of the list rather than -the back. However, the standard library <tt>stack</tt> adaptor cannot support -this. -</p> - -<p> -It would be relatively easy to write a partial specialization for <tt>stack</tt> -to support <tt>forward_list</tt>, but that opens the question of which header to -place it in. A much better solution would be to add a <tt>concept_map</tt> for -the <tt>StackLikeContainer</tt> concept to the <tt><forward_list></tt> header and then -everything just works, including a user's own further uses in a -stack-like context. -</p> - -<p> -Therefore while I am submitting the issue now so that it is on record, I -<em>strongly recommend</em> we resolve as "NAD Concepts" as any non-concepts -based solution will be inferior to the final goal, and the feature is -not so compelling it must be supported ahead of the concepts-based -library. -</p> - -<p><i>[ -2009-11-02 Howard adds: -]</i></p> - - -<blockquote><p> -Moved to Tentatively NAD Concepts after 5 positive votes on c++std-lib. -</p></blockquote> - - -<p><b>Rationale:</b></p> -<p> -Any non-concepts based solution will be inferior to the final goal, and the -feature is not so compelling it must be supported ahead of the concepts-based -library. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1190"></a>1190. Setting the maximum load factor should return the previous value</h3> -<p><b>Section:</b> 23.2.5 [unord.req], 23.5 [unord] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2009-08-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#unord.req">active issues</a> in [unord.req].</p> -<p><b>View all other</b> <a href="lwg-index.html#unord.req">issues</a> in [unord.req].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The unordered associative container requirements table specifies that -<tt>a.set_max_load_factor(z)</tt> has return type <tt>void</tt>. However, there is a -useful piece of information to return: the previous value. Users who -don't need it can always ignore it. -</p> - - -<p><i>[ -2010 Rapperswil: -]</i></p> - - -<blockquote><p> -The benefit seems minor, while breaking with the getter/setter idiom these overloads support. - -Move to Tentatively NAD. -</p></blockquote> - -<p><i>[ -Moved to NAD at 2010-11 Batavia -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -In the unordered associative container requirements table, change: -</p> - -<blockquote> -<table border="1"> -<caption>Table 87 — Unordered associative container requirements -(in addition to container)</caption> - -<tr> -<th>Expression</th><th>Return type</th><th>Assertion/note pre-/post-condition</th> -<th>Complexity</th> -</tr> - -<tr> -<td><tt>a.max_load_factor(z)</tt></td> -<td><tt><del>void</del> <ins>float</ins></tt></td> -<td>Pre: <tt>z</tt> shall be positive. Changes the container's maximum -<del>load</del> load factor, using <tt>z</tt> as a hint. -<ins>Returns: the previous value of -<tt>a.max_load_factor()</tt>.</ins> -</td> -<td> -constant -</td> -</tr> -</table> -</blockquote> - -<p> -Change the return type of <tt>set_max_load_factor</tt> -in the class synopses in 23.5.4 [unord.map], 23.5.5 [unord.multimap], 23.5.6 [unord.set], -and 23.5.7 [unord.multiset]. -</p> - -<p> -If issue <a href="lwg-active.html#1188">1188</a> is also accepted, make the same changes for -<tt>min_load_factor</tt>. -</p> - - - - - -<hr> -<h3><a name="1200"></a>1200. "surprising" <tt>char_traits<T>::int_type</tt> requirements</h3> -<p><b>Section:</b> 21.2.2 [char.traits.typedefs] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Sean Hunt <b>Opened:</b> 2009-09-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#char.traits.typedefs">issues</a> in [char.traits.typedefs].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The footnote for <tt>int_type</tt> in 21.2.2 [char.traits.typedefs] says that -</p> - -<blockquote><p> -If <tt>eof()</tt> can be held in <tt>char_type</tt> then some iostreams implementations -may give surprising results. -</p></blockquote> - -<p> -This implies that <tt>int_type</tt> should be a superset of -<tt>char_type</tt>. However, the requirements for <tt>char16_t</tt> and <tt>char32_t</tt> define -<tt>int_type</tt> to be equal to <tt>int_least16_t</tt> and <tt>int_least32_t</tt> respectively. -<tt>int_least16_t</tt> is likely to be the same size as <tt>char_16_t</tt>, which may lead -to surprising behavior, even if <tt>eof()</tt> is not a valid UTF-16 code unit. -The standard should not prescribe surprising behavior, especially -without saying what it is (it's apparently not undefined, just -surprising). The same applies for 32-bit types. -</p> - -<p> -I personally recommend that behavior be undefined if <tt>eof()</tt> is a member -of <tt>char_type</tt>, and another type be chosen for <tt>int_type</tt> (my personal -favorite has always been a <tt>struct {bool eof; char_type c;}</tt>). -Alternatively, the exact results of such a situation should be defined, -at least so far that I/O could be conducted on these types as long as -the code units remain valid. Note that the argument that no one streams -<tt>char16_t</tt> or <tt>char32_t</tt> is not really valid as it would be perfectly -reasonable to use a <tt>basic_stringstream</tt> in conjunction with UTF character -types. -</p> - -<p><i>[ -2009-10-28 Ganesh provides two possible resolutions and expresses a preference -for the second: -]</i></p> - - -<blockquote> -<ol> -<li> -<p> -Replace 21.2.3.2 [char.traits.specializations.char16_t] para 3 with: -</p> - -<blockquote><p> -The member <tt>eof()</tt> shall return <del>an implementation-defined -constant that cannot appear as a valid UTF-16 code unit</del> -<ins><tt>UINT_LEAST16_MAX</tt> [<i>Note:</i> this value is guaranteed to -be a permanently reserved UCS-2 code position if <tt>UINT_LEAST16_MAX == -0xFFFF</tt> and it's not a UCS-2 code position otherwise — <i>end -note</i>]</ins>. -</p></blockquote> - -<p> -Replace 21.2.3.3 [char.traits.specializations.char32_t] para 3 with: -</p> - -<blockquote><p> -The member <tt>eof()</tt> shall return <del>an implementation-defined constant that -cannot appear as a Unicode code point</del> -<ins> -<tt>UINT_LEAST32_MAX</tt> [<i>Note:</i> this value is guaranteed to be a -permanently reserved UCS-4 code position if <tt>UINT_LEAST32_MAX == -0xFFFFFFFF</tt> and it's not a UCS-4 code position otherwise — <i>end -note</i>]</ins>. -</p></blockquote> -</li> -<li> -<p> -In 21.2.3.2 [char.traits.specializations.char16_t], in the -definition of <tt>char_traits<char16_t></tt> replace the definition of nested -typedef <tt>int_type</tt> with: -</p> - -<blockquote><pre> -namespace std { - template<> struct char_traits<char16_t> { - typedef char16_t char_type; - typedef <del>uint_least16_t</del> <ins>uint_fast16_t</ins> int_type; - ... -</pre></blockquote> - -<p> -Replace 21.2.3.2 [char.traits.specializations.char16_t] para 3 with: -</p> - -<blockquote><p> -The member <tt>eof()</tt> shall return <del>an implementation-defined -constant that cannot appear as a valid UTF-16 code unit</del> -<ins><tt>UINT_FAST16_MAX</tt> [<i>Note:</i> this value is guaranteed to -be a permanently reserved UCS-2 code position if <tt>UINT_FAST16_MAX == -0xFFFF</tt> and it's not a UCS-2 code position otherwise — <i>end -note</i>]</ins>. -</p></blockquote> - -<p> -In 21.2.3.3 [char.traits.specializations.char32_t], in the -definition of <tt>char_traits<char32_t></tt> replace the definition of nested -typedef <tt>int_type</tt> with: -</p> - -<blockquote><pre> -namespace std { - template<> struct char_traits<char32_t> { - typedef char32_t char_type; - typedef <del>uint_least32_t</del> <ins>uint_fast32_t</ins> int_type; - ... -</pre></blockquote> - -<p> -Replace 21.2.3.3 [char.traits.specializations.char32_t] para 3 with: -</p> - -<blockquote><p> -The member <tt>eof()</tt> shall return <del>an implementation-defined constant that -cannot appear as a Unicode code point</del> -<ins> -<tt>UINT_FAST32_MAX</tt> [<i>Note:</i> this value is guaranteed to be a -permanently reserved UCS-4 code position if <tt>UINT_FAST32_MAX == -0xFFFFFFFF</tt> and it's not a UCS-4 code position otherwise — <i>end -note</i>]</ins>. -</p></blockquote> -</li> -</ol> -</blockquote> - - -<p><i>[ -2010 Rapperswil: -]</i></p> - - -<blockquote><p> -This seems an overspecification, and it is not clear what problem is being solved - -these values can be used portably by using the named functions; there is no need -for the value itself to be portable. - -Move to Tentatively NAD. -</p></blockquote> - -<p><i>[ -Moved to NAD at 2010-11 Batavia -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="1202"></a>1202. <tt>integral_constant</tt> needs a spring clean</h3> -<p><b>Section:</b> 20.10.3 [meta.help] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-09-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.help">issues</a> in [meta.help].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The specification of <tt>integral_constant</tt> has been inherited -essentially unchanged from TR1: -</p> - -<blockquote><pre> -template <class T, T v> -struct integral_constant { - static const T value = v; - typedef T value_type; - typedef integral_constant<T,v> type; -}; -</pre></blockquote> - -<p> -In light of 0x language changes there are several things we might -consider changing, notably the form of specification for value. -</p> - -<p> -The current form requires a static data member have storage allocated -for it, where we could now implement without this using the new enum -syntax: -</p> - -<blockquote><pre> -template <class T, T v> -struct integral_constant { - <b>enum : T { value = v };</b> - typedef T value_type; - typedef integral_constant type; -}; -</pre></blockquote> - -<p> -The effective difference between these two implementation is: -</p> - -<ol style="list-style-type:lower-roman"> -<li> -No requirement to allocate storage for data member (which we hope but do -not guarantee compilers strip today) -</li> - -<li> -You can no longer take the address of the constant as -<tt>&integral_constant<T,v>::value;</tt> -</li> -</ol> - -<p> -Also note the editorial change to drop the explicit qualification of -<tt>integral_constant</tt> in the <tt>typedef type</tt>. This makes it quite clear we -mean the current instantiation, and cannot be mistaken for a recursive -metaprogram. -</p> - -<p> -Even if we don't mandate this implementation, it would be nice to give -vendors freedom under QoI to choose their preferred representation. -</p> - -<p> -The other side of this issue is if we choose to retain the static -constant form. In that case we should go further and insist on -<tt>constexpr</tt>, much like we did throughout <tt>numeric_limits</tt>: -</p> - -<blockquote><pre> -template <class T, T v> -struct integral_constant { - static <b>constexpr</b> T value = v; - typedef T value_type; - typedef integral_constant type; -}; -</pre></blockquote> - -<p> -[Footnote] It turns out <tt>constexpr</tt> is part of the Tentatively Ready -resolution for <a href="lwg-defects.html#1019">1019</a>. I don't want to interfere with that issue, but -would like a new issue to consider if the fixed-base enum implementation -should be allowed. -</p> - -<p><i>[ -2009-09-05 Daniel adds: -]</i></p> - - -<blockquote> -<p> -I think that the suggested resolution is incomplete and -may have some possible unwanted side-effects. To understand -why, note that <tt>integral_constant</tt> is <em>completely</em> specified -by code in 20.10.3 [meta.help]. While this is usually considered -as a good thing, let me give a possible user-defined -specialization that would break given the suggested changes: -</p> - -<blockquote><pre> -enum NodeColor { Red, Black }; - -std::integral_constant<NodeColor, Red> red; -</pre></blockquote> - -<p> -The reason why that breaks is due to the fact that -current core language rules does only allow integral -types as enum-bases, see 7.2 [dcl.enum]/2. -</p> - -<p> -So, I think that we cannot leave the implementation the -freedom to decide which way they would like to provide -the implementation, because that is easily user-visible -(I don't speak of addresses, but of instantiation errors), -therefore if applied, this should be either specified or -wording must be added that gives a note about this -freedom of implementation. -</p> - -<p> -Another possible disadvantage seems to me that user-expectations -are easy to disappoint if they see a failure -of the test -</p> - -<blockquote><pre> -assert(typeid(std::integral_constant<int, 0>::value) == typeid(int)); -</pre></blockquote> - -<p> -or of -</p> - -<blockquote><pre> -static_assert(std::is_same<decltype(std::integral_constant<int, 0>::value), const int>::value, "Bad library"); -</pre></blockquote> - -</blockquote> - -<p><i>[ -2010-01-14 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -We think that the suggested resolution is incomplete and may have some possible -unwanted side-effects. (see Daniel's 2009-09-05 comment for details). -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1219"></a>1219. unique_lock::lock and resource_deadlock_would_occur</h3> -<p><b>Section:</b> 30.4.2.2.2 [thread.lock.unique.locking] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Jeffrey Yasskin <b>Opened:</b> 2009-09-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.lock.unique.locking">issues</a> in [thread.lock.unique.locking].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1159">1159</a></p> -<p><b>Discussion:</b></p> - - - -<p> -<tt>unique_lock::lock</tt> and friends raise -"<tt>resource_deadlock_would_occur</tt> -- if the current thread already -owns the mutex (i.e., on entry, <tt>owns</tt> is <tt>true</tt>)." 1) -The current thread owning a mutex is not the same as any particular -<tt>unique_lock::owns</tt> being <tt>true</tt>. 2) There's no need to -raise this exception for a <tt>recursive_mutex</tt> if <tt>owns</tt> is -<tt>false</tt>. 3) If <tt>owns</tt> is true, we need to raise some -exception or the unique_lock will lose track of whether to unlock itself -on destruction, but "deadlock" isn't it. For (3), s/bool owns/int -ownership_level/ would fix it. -</p> - -<p><i>[ -2009-11-11 Alisdair notes that this issue is very closely related to <a href="lwg-defects.html#1159">1159</a>, -if not a dup. -]</i></p> - - -<p><i>[ -2009-11-14 Moved to Tentatively Dup after 5 positive votes on c++std-lib. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1223"></a>1223. condition_variable_any lock matching?</h3> -<p><b>Section:</b> 30.5.2 [thread.condition.condvarany] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Jeffrey Yasskin <b>Opened:</b> 2009-09-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.condition.condvarany">issues</a> in [thread.condition.condvarany].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -For <tt>condition_variable_any</tt>, must all lock arguments to concurrent wait calls -"match" in some way, similar to the requirement in -30.5.1 [thread.condition.condvar] that <tt>lock.mutex()</tt> returns the same -value for each of the lock arguments supplied by all concurrently -waiting threads (via <tt>wait</tt> or <tt>timed_wait</tt>)? -</p> - -<p><i>[ -2010-02-12 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -The rationale is that it doesn't matter, and you can't check: the lock types may -be different, or the same and user-defined, so the implementation must provide -internal synchronization anyway. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1224"></a>1224. condition_variable_any support for recursive mutexes?</h3> -<p><b>Section:</b> 30.5.2 [thread.condition.condvarany] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Jeffrey Yasskin <b>Opened:</b> 2009-09-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.condition.condvarany">issues</a> in [thread.condition.condvarany].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -For <tt>condition_variable_any</tt>, are recursive mutexes allowed? (I think "no") -</p> - -<p><i>[ -2009-11-17 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p> -<tt>condition_variable_any::wait</tt> accepts any type of mutex. It calls -<tt>unlock</tt> precisely once on entry and <tt>lock</tt> precisely once on -exit. It is up to the user to ensure that this provides the required -synchronization. Use of a recursive mutex is safe if either its lock count is 1, -so after the single unlock it can be acquired by another thread, or another -mechanism is used to synchronize the data. -</p> - - - - - -<hr> -<h3><a name="1228"></a>1228. User-specialized nothrow type traits</h3> -<p><b>Section:</b> 20.10.4.3 [meta.unary.prop] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-10-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#meta.unary.prop">active issues</a> in [meta.unary.prop].</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.unary.prop">issues</a> in [meta.unary.prop].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -According to p1 20.10.2 [meta.type.synop]: -</p> - -<blockquote><p> -The behavior of a program that adds specializations for any of the class -templates defined in this subclause is undefined unless otherwise -specified. -</p></blockquote> - -<p> -I believe we should 'otherwise specify' for the nothrow traits, are -these are exactly the use cases where the end user actually has more -information than the compiler. -</p> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Moved to Open. Definitely need to give the users the ability to ensure -that the traits give the right answers. Unsure we want to give them the -ability to say this in more than one way. Believes the noexcept proposal -already gives this. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: Moved to NAD, rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -We believe the solution offered by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3050.html">N3050</a> -is superior. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add the following comment: -</p> - -<blockquote><p> -user specialization permitted to derive from <tt>std::true_type</tt> when the -operation is known not to throw. -</p></blockquote> - -<p> -to the following traits in 20.10.4.3 [meta.unary.prop] Table 43 Type -property predicates. -</p> - -<p><i>[ -This may require a new Comments column -]</i></p> - - -<blockquote><pre> -has_nothrow_default_constructor -has_nothrow_copy_constructor -has_nothrow_assign -</pre></blockquote> - - - - - -<hr> -<h3><a name="1230"></a>1230. <tt>mem_fn</tt> and variadic templates</h3> -<p><b>Section:</b> 20.9.11 [func.memfn] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-10-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#func.memfn">issues</a> in [func.memfn].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#920">920</a></p> -<p><b>Discussion:</b></p> - - - -<p> -Since we have removed the entry in B [implimits] for the -library-specific limit for number of arguments passed to -<tt>function</tt>/<tt>tuple</tt>/etc. I believe we need to update the -spec for <tt>mem_fn</tt> to reflect this. -</p> - -<p> -The "<i>Remarks:</i> Implementations may implement <tt>mem_fn</tt> as a set of -overloaded function templates." no longer holds, as we cannot create an -arbitrary number of such overloads. I believe we should strike the -remark and add a second signature: -</p> - -<blockquote><pre> -template<class R, class T, typename ... ArgTypes> - unspecified mem_fn(R (T::*pm)(ArgTypes...)); -</pre></blockquote> - -<p> -I believe we need two signatures as pointer-to-data-member and -pointer-to-member-function-taking-no-args appear to use subtly different -syntax. -</p> - -<p><i>[ -<a href="lwg-defects.html#920">920</a> as a similar proposed resolution. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add to 20.9 [function.objects] and 20.9.11 [func.memfn]: -</p> -<blockquote><pre> -template<class R, class T> <i>unspecified</i> mem_fn(R T::* pm) - -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...));</ins> -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const);</ins> -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...) volatile);</ins> -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const volatile);</ins> - -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...)&);</ins> -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const&);</ins> -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...) volatile&);</ins> -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const volatile&);</ins> - -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...)&&);</ins> -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const&&);</ins> -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...) volatile&&);</ins> -<ins>template<class R, class T, class ...Args> <i>unspecified</i> mem_fn(R (T::* pm)(Args...) const volatile&&);</ins> -</pre></blockquote> - -<p> -Strike 20.9.11 [func.memfn], p5: -</p> - -<blockquote><p> -<del><i>Remarks:</i> Implementations may implement <tt>mem_fn</tt> as a set -of overloaded function templates.</del> -</p></blockquote> - - - - - - -<hr> -<h3><a name="1232"></a>1232. Still <tt>swap</tt>'s with rvalue-references</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2009-10-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The current library contains still rvalue reference-swaps that seem to be -overlooked in the process of switching back to lvalue-ref swaps. -</p> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Editor accepts as NAD Editorial. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -<p> -Change 20.3 [pairs]/1 as indicated: -</p> - -<blockquote><pre> -template <class T1, class T2> -struct pair { - ... - void swap(pair&<del>&</del> p); -}; -</pre></blockquote> -</li> - -<li> -<p> -Change 20.3 [pairs] before p. 17 as indicated: -</p> - -<blockquote><pre> -void swap(pair&<del>&</del> p); -</pre></blockquote> - -</li> - -<li> - -<p> -Change 20.3 [pairs] before p. 21 as indicated: -</p> - -<blockquote><pre> -template<class T1, class T2> void swap(pair<T1, T2>& x, pair<T1, T2>& y); -<del>template<class T1, class T2> void swap(pair<T1, T2>&& x, pair<T1, T2>& y);</del> -<del>template<class T1, class T2> void swap(pair<T1, T2>& x, pair<T1, T2>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 20.4.1 [tuple.general]/2, header <tt><tuple></tt> synopsis, as indicated: -</p> - -<blockquote><pre> -// 20.5.2.9, specialized algorithms: -template <class... Types> -void swap(tuple<Types...>& x, tuple<Types...>& y); -<del>template <class... Types> -void swap(tuple<Types...>&& x, tuple<Types...>& y); -template <class... Types> -void swap(tuple<Types...>& x, tuple<Types...>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 20.4.2 [tuple.tuple] as indicated: -</p> - -<blockquote><pre> -// 20.5.2.3, tuple swap -void swap(tuple&<del>&</del>) -</pre></blockquote> - -</li> - -<li> -<p> -Change 20.4.2.3 [tuple.swap] before 1 as indicated: -</p> - -<blockquote><pre> -void swap(tuple&<del>&</del> rhs); -</pre></blockquote> - -</li> - -<li> -<p> -Change 20.9 [function.objects]/2, header <tt><functional></tt> synopsis, as indicated: -</p> - -<blockquote><pre> -template<class R, class... ArgTypes> -void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&); -<del>template<class R, class... ArgTypes> -void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&); -template<class R, class... ArgTypes> -void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)&&);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 20.9.12.2 [func.wrap.func], as indicated: -</p> - -<blockquote><pre> -// 20.7.15.2.2, function modifiers: -void swap(function&<del>&</del>); -template<class F, class A> void assign(F, const A&); - -[..] - -// 20.7.15.2.7, specialized algorithms: -template <class R, class... ArgTypes> -void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&); -<del>template <class R, class... ArgTypes> -void swap(function<R(ArgTypes...)>&&, function<R(ArgTypes...)>&); -template <class R, class... ArgTypes> -void swap(function<R(ArgTypes...)>&, function<R(ArgTypes...)>&&);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 20.9.12.2.7 [func.wrap.func.alg] before 1 as indicated: -</p> - -<blockquote><pre> -template<class R, class... ArgTypes> -void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>& f2); -<del>template<class R, class... ArgTypes> -void swap(function<R(ArgTypes...)>&& f1, function<R(ArgTypes...)>& f2); -template<class R, class... ArgTypes> -void swap(function<R(ArgTypes...)>& f1, function<R(ArgTypes...)>&& f2);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 20.8.2.2 [util.smartptr.shared]/1 as indicated: -</p> - -<blockquote><pre> -// 20.8.12.2.4, modifiers: -void swap(shared_ptr&<del>&</del> r); - -[..] - -// 20.8.12.2.9, shared_ptr specialized algorithms: -template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>& b); -<del>template<class T> void swap(shared_ptr<T>&& a, shared_ptr<T>& b); -template<class T> void swap(shared_ptr<T>& a, shared_ptr<T>&& b);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 21.3 [string.classes]/1, header <tt><string></tt> synopsis, as indicated: -</p> - -<blockquote><pre> -// 21.4.8.8: swap -template<class charT, class traits, class Allocator> -void swap(basic_string<charT,traits,Allocator>& lhs, basic_string<charT,traits,Allocator>& rhs); -<del>template<class charT, class traits, class Allocator> -void swap(basic_string<charT,traits,Allocator>&& lhs, basic_string<charT,traits,Allocator>& rhs); -template<class charT, class traits, class Allocator> -void swap(basic_string<charT,traits,Allocator>& lhs, basic_string<charT,traits,Allocator>&& rhs);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3 [sequences]/1, header <tt><deque></tt> synopsis, as indicated: -</p> - -<blockquote><pre> -template <class T, class Allocator> -void swap(deque<T,Allocator>& x, deque<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(deque<T,Allocator>&& x, deque<T,Allocator>& y); -template <class T, class Allocator> -void swap(deque<T,Allocator>& x, deque<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3 [sequences]/1, header <tt><list></tt> synopsis, as indicated: -</p> - -<blockquote><pre> -template <class T, class Allocator> -void swap(list<T,Allocator>& x, list<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(list<T,Allocator>&& x, list<T,Allocator>& y); -template <class T, class Allocator> -void swap(list<T,Allocator>& x, list<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3 [sequences]/1, header <tt><queue></tt> synopsis, as indicated: -</p> - -<blockquote><pre> -template <class T, class Allocator> -void swap(queue<T, Container>& x, queue<T, Container>& y); -<del>template <class T, class Container> -void swap(queue<T, Container>&& x, queue<T, Container>& y); -template <class T, class Container> -void swap(queue<T, Container>& x, queue<T, Container>&& y);</del> - -template <class T, class Container = vector<T>, class Compare = less<typename Container::value_type> > -class priority_queue; -template <class T, class Container, class Compare> -void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>& y); -<del>template <class T, class Container, class Compare> -void swap(priority_queue<T, Container, Compare>&& x, priority_queue<T, Container, Compare>& y); -template <class T, class Container, class Compare> -void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3 [sequences]/1, header <tt><stack></tt> synopsis, as indicated: -</p> - -<blockquote><pre> -template <class T, class Container> -void swap(stack<T, Container>& x, stack<T, Container>& y); -<del>template <class T, class Container> -void swap(stack<T, Container>&& x, stack<T, Container>& y); -template <class T, class Container> -void swap(stack<T, Container>& x, stack<T, Container>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3 [sequences]/1, header <tt><vector></tt> synopsis, as indicated: -</p> - -<blockquote><pre> -template <class T, class Allocator> -void swap(vector<T,Allocator>& x, vector<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(vector<T,Allocator>&& x, vector<T,Allocator>& y); -template <class T, class Allocator> -void swap(vector<T,Allocator>& x, vector<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.3 [deque]/2 as indicated: -</p> - -<blockquote><pre> -iterator erase(const_iterator position); -iterator erase(const_iterator first, const_iterator last); -void swap(deque<T,Allocator>&<del>&</del>); -void clear(); - -[..] - -// specialized algorithms: -template <class T, class Allocator> -void swap(deque<T,Allocator>& x, deque<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(deque<T,Allocator>&& x, deque<T,Allocator>& y); -template <class T, class Allocator> -void swap(deque<T,Allocator>& x, deque<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.3.5 [deque.special] as indicated: -</p> - -<blockquote><pre> -template <class T, class Allocator> -void swap(deque<T,Allocator>& x, deque<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(deque<T,Allocator>&& x, deque<T,Allocator>& y); -template <class T, class Allocator> -void swap(deque<T,Allocator>& x, deque<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.4 [forwardlist]/2 as indicated: -</p> - -<blockquote><pre> -iterator erase_after(const_iterator position); -iterator erase_after(const_iterator position, iterator last); -void swap(forward_list<T,Allocator>&<del>&</del>); - -[..] - -// 23.3.3.6 specialized algorithms: -template <class T, class Allocator> -void swap(forward_list<T,Allocator>& x, forward_list<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(forward_list<T,Allocator>&& x, forward_list<T,Allocator>& y); -template <class T, class Allocator> -void swap(forward_list<T,Allocator>& x, forward_list<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.4.7 [forwardlist.spec] as indicated: -</p> - -<blockquote><pre> -template <class T, class Allocator> -void swap(forward_list<T,Allocator>& x, forward_list<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(forward_list<T,Allocator>&& x, forward_list<T,Allocator>& y); -template <class T, class Allocator> -void swap(forward_list<T,Allocator>& x, forward_list<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.5 [list]/2 as indicated: -</p> - -<blockquote><pre> -iterator erase(const_iterator position); -iterator erase(const_iterator position, const_iterator last); -void swap(list<T,Allocator>&<del>&</del>); -void clear(); - -[..] - -// specialized algorithms: -template <class T, class Allocator> -void swap(list<T,Allocator>& x, list<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(list<T,Allocator>&& x, list<T,Allocator>& y); -template <class T, class Allocator> -void swap(list<T,Allocator>& x, list<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.5.6 [list.special] as indicated: -</p> - -<blockquote><pre> -template <class T, class Allocator> -void swap(list<T,Allocator>& x, list<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(list<T,Allocator>&& x, list<T,Allocator>& y); -template <class T, class Allocator> -void swap(list<T,Allocator>& x, list<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.6.3.1 [queue.defn] as indicated: -</p> - -<blockquote><pre> -void swap(queue&<del>&</del> q) { c.swap(q.c); } - -[..] - -template <class T, class Container> -void swap(queue<T, Container>& x, queue<T, Container>& y); -<del>template <class T, class Container> -void swap(queue<T, Container>&& x, queue<T, Container>& y); -template <class T, class Container> -void swap(queue<T, Container>& x, queue<T, Container>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.6.3.5 [queue.special] as indicated: -</p> - -<blockquote><pre> -template <class T, class Container> -void swap(queue<T, Container>& x, queue<T, Container>& y); -<del>template <class T, class Container> -void swap(queue<T, Container>&& x, queue<T, Container>& y); -template <class T, class Container> -void swap(queue<T, Container>& x, queue<T, Container>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.6.4 [priority.queue]/1 as indicated: -</p> - -<blockquote><pre> -void swap(priority_queue&<del>&</del>); - -// no equality is provided -template <class T, class Container, class Compare> -void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>& y); -<del>template <class T, class Container, class Compare> -void swap(priority_queue<T, Container, Compare>&& x, priority_queue<T, Container, Compare>& y); -template <class T, class Container, class Compare> -void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.6.4.4 [priqueue.special] as indicated: -</p> - -<blockquote><pre> -template <class T, class Container, Compare> -void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>& y); -<del>template <class T, class Container, Compare> -void swap(priority_queue<T, Container, Compare>&& x, priority_queue<T, Container, Compare>& y); -template <class T, class Container, Compare> -void swap(priority_queue<T, Container, Compare>& x, priority_queue<T, Container, Compare>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.6.5.2 [stack.defn] as indicated: -</p> - -<blockquote><pre> -void swap(stack&<del>&</del> s) { c.swap(s.c); } - -[..] - -template <class T, class Allocator> -void swap(stack<T,Allocator>& x, stack<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(stack<T,Allocator>&& x, stack<T,Allocator>& y); -template <class T, class Allocator> -void swap(stack<T,Allocator>& x, stack<T,Allocator>&& y);</del> -</pre></blockquote> - - -</li> - -<li> -<p> -Change 23.6.5.6 [stack.special] as indicated: -</p> - -<blockquote><pre> -template <class T, class Container> -void swap(stack<T, Container>& x, stack<T, Container>& y); -<del>template <class T, class Container> -void swap(stack<T, Container>&& x, stack<T, Container>& y); -template <class T, class Container> -void swap(stack<T, Container>& x, stack<T, Container>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.6 [vector]/2 as indicated: -</p> - -<blockquote><pre> -void swap(vector<T,Allocator>&<del>&</del>); -void clear(); - -[..] - -// specialized algorithms: -template <class T, class Allocator> -void swap(vector<T,Allocator>& x, vector<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(vector<T,Allocator>&& x, vector<T,Allocator>& y); -template <class T, class Allocator> -void swap(vector<T,Allocator>& x, vector<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.6.3 [vector.capacity] before p. 8 as indicated: -</p> - -<blockquote><pre> -void swap(vector<T,Allocator>&<del>&</del> x); -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.6.6 [vector.special] as indicated: -</p> - -<blockquote><pre> -template <class T, class Allocator> -void swap(vector<T,Allocator>& x, vector<T,Allocator>& y); -<del>template <class T, class Allocator> -void swap(vector<T,Allocator>&& x, vector<T,Allocator>& y); -template <class T, class Allocator> -void swap(vector<T,Allocator>& x, vector<T,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.3.7 [vector.bool]/1 as indicated: -</p> - -<blockquote><pre> -iterator erase(const_iterator first, const_iterator last); -void swap(vector<bool,Allocator>&<del>&</del>); -static void swap(reference x, reference y); -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.4 [associative]/1, header <tt><map></tt> synopsis as indicated: -</p> - -<blockquote><pre> -template <class Key, class T, class Compare, class Allocator> -void swap(map<Key,T,Compare,Allocator>& x, map<Key,T,Compare,Allocator>& y); -<del>template <class Key, class T, class Compare, class Allocator> -void swap(map<Key,T,Compare,Allocator&& x, map<Key,T,Compare,Allocator>& y); -template <class Key, class T, class Compare, class Allocator> -void swap(map<Key,T,Compare,Allocator& x, map<Key,T,Compare,Allocator>&& y);</del> - -[..] - -template <class Key, class T, class Compare, class Allocator> -void swap(multimap<Key,T,Compare,Allocator>& x, multimap<Key,T,Compare,Allocator>& y); -<del>template <class Key, class T, class Compare, class Allocator> -void swap(multimap<Key,T,Compare,Allocator&& x, multimap<Key,T,Compare,Allocator>& y); -template <class Key, class T, class Compare, class Allocator> -void swap(multimap<Key,T,Compare,Allocator& x, multimap<Key,T,Compare,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.4 [associative]/1, header <tt><set></tt> synopsis as indicated: -</p> - -<blockquote><pre> -template <class Key, class Compare, class Allocator> -void swap(set<Key,Compare,Allocator>& x, set<Key,Compare,Allocator>& y); -<del>template <class Key, class T, class Compare, class Allocator> -void swap(set<Key,T,Compare,Allocator&& x, set<Key,T,Compare,Allocator>& y); -template <class Key, class T, class Compare, class Allocator> -void swap(set<Key,T,Compare,Allocator& x, set<Key,T,Compare,Allocator>&& y);</del> - -[..] - -template <class Key, class Compare, class Allocator> -void swap(multiset<Key,Compare,Allocator>& x, multiset<Key,Compare,Allocator>& y); -<del>template <class Key, class T, class Compare, class Allocator> -void swap(multiset<Key,T,Compare,Allocator&& x, multiset<Key,T,Compare,Allocator>& y); -template <class Key, class T, class Compare, class Allocator> -void swap(multiset<Key,T,Compare,Allocator& x, multiset<Key,T,Compare,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.4.4 [map]/2 as indicated: -</p> - -<blockquote><pre> -iterator erase(const_iterator first, const_iterator last); -void swap(map<Key,T,Compare,Allocator>&<del>&</del>); -void clear(); - -[..] - -// specialized algorithms: -template <class Key, class T, class Compare, class Allocator> -void swap(map<Key,T,Compare,Allocator>& x, map<Key,T,Compare,Allocator>& y); -<del>template <class Key, class T, class Compare, class Allocator> -void swap(map<Key,T,Compare,Allocator&& x, map<Key,T,Compare,Allocator>& y); -template <class Key, class T, class Compare, class Allocator> -void swap(map<Key,T,Compare,Allocator& x, map<Key,T,Compare,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.4.4.5 [map.special] as indicated: -</p> - -<blockquote><pre> -template <class Key, class T, class Compare, class Allocator> -void swap(map<Key,T,Compare,Allocator>& x, map<Key,T,Compare,Allocator>& y); -<del>template <class Key, class T, class Compare, class Allocator> -void swap(map<Key,T,Compare,Allocator>&& x, map<Key,T,Compare,Allocator>& y); -template <class Key, class T, class Compare, class Allocator> -void swap(map<Key,T,Compare,Allocator>& x, map<Key,T,Compare,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.4.5 [multimap]/2 as indicated: -</p> - -<blockquote><pre> -iterator erase(const_iterator first, const_iterator last); -void swap(multimap<Key,T,Compare,Allocator>&<del>&</del>); -void clear(); - -[..] - -// specialized algorithms: -template <class Key, class T, class Compare, class Allocator> -void swap(multimap<Key,T,Compare,Allocator>& x, multimap<Key,T,Compare,Allocator>& y); -<del>template <class Key, class T, class Compare, class Allocator> -void swap(multimap<Key,T,Compare,Allocator&& x, multimap<Key,T,Compare,Allocator>& y); -template <class Key, class T, class Compare, class Allocator> -void swap(multimap<Key,T,Compare,Allocator& x, multimap<Key,T,Compare,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.4.5.4 [multimap.special] as indicated: -</p> - -<blockquote><pre> -template <class Key, class T, class Compare, class Allocator> -void swap(multimap<Key,T,Compare,Allocator>& x, multimap<Key,T,Compare,Allocator>& y); -<del>template <class Key, class T, class Compare, class Allocator> -void swap(multimap<Key,T,Compare,Allocator>&& x, multimap<Key,T,Compare,Allocator>& y); -template <class Key, class T, class Compare, class Allocator> -void swap(multimap<Key,T,Compare,Allocator>& x, multimap<Key,T,Compare,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.4.6 [set]/2 and 23.4.6.3 [set.special] as indicated: (twice!) -</p> - -<blockquote><pre> -// specialized algorithms: -template <class Key, class Compare, class Allocator> -void swap(set<Key,Compare,Allocator>& x, set<Key,Compare,Allocator>& y); -<del>template <class Key, class Compare, class Allocator> -void swap(set<Key,Compare,Allocator&& x, set<Key,Compare,Allocator>& y); -template <class Key, class Compare, class Allocator> -void swap(set<Key,Compare,Allocator& x, set<Key,Compare,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.4.7 [multiset]/2 as indicated: -</p> - -<blockquote><pre> -iterator erase(const_iterator first, const_iterator last); -void swap(multiset<Key,Compare,Allocator>&<del>&</del>); -void clear(); - -[..] - -// specialized algorithms: -template <class Key, class Compare, class Allocator> -void swap(multiset<Key,Compare,Allocator>& x, multiset<Key,Compare,Allocator>& y); -<del>template <class Key, class Compare, class Allocator> -void swap(multiset<Key,Compare,Allocator&& x, multiset<Key,Compare,Allocator>& y); -template <class Key, class Compare, class Allocator> -void swap(multiset<Key,Compare,Allocator& x, multiset<Key,Compare,Allocator>&& y);</del> -</pre></blockquote> - -</li> - -<li> -<p> -Change 23.4.7.3 [multiset.special] as indicated: -</p> - -<blockquote><pre> -template <class Key, class Compare, class Allocator> -void swap(multiset<Key,Compare,Allocator>& x, multiset<Key,Compare,Allocator>& y); -<del>template <class Key, class Compare, class Allocator> -void swap(multiset<Key,Compare,Allocator>&& x, multiset<Key,Compare,Allocator>& y); -template <class Key, class Compare, class Allocator> -void swap(multiset<Key,Compare,Allocator>& x, multiset<Key,Compare,Allocator>&& y);</del> -</pre></blockquote> - -</li> -</ol> - - - - - -<hr> -<h3><a name="1233"></a>1233. Missing <tt>unique_ptr</tt> signatures in synopsis</h3> -<p><b>Section:</b> 20.7 [memory] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2009-10-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#memory">issues</a> in [memory].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Related to <a href="lwg-defects.html#296">296</a>. Some <tt>unique_ptr</tt> signatures are missing -from the synopsis in 20.7 [memory]. -</p> - -<p><i>[ -2009-11-04 Howard adds: -]</i></p> - - -<blockquote><p> -Moved to Tentatively NAD Editorial. The editor has adopted the fix. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -Add in 20.7 [memory], Header <tt><memory></tt> synopsis -missing declarations as shown below: -</p> - -<blockquote><pre> -// 20.8.11 Class unique_ptr: -template <class X> class default_delete; -<ins>template<class T> struct default_delete<T[]>;</ins> -template <class X, class D = default_delete<T>> class unique_ptr; -<ins>template<class T, class D> class unique_ptr<T[], D>;</ins> - -<ins>template<class T, class D> void swap(unique_ptr<T, D>& x, unique_ptr<T, D>& y);</ins> - -<ins>template<class T1, class D1, class T2, class D2> -bool operator==(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);</ins> -<ins>template<class T1, class D1, class T2, class D2> -bool operator!=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);</ins> -<ins>template<class T1, class D1, class T2, class D2> -bool operator<(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);</ins> -<ins>template<class T1, class D1, class T2, class D2> -bool operator<=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);</ins> -<ins>template<class T1, class D1, class T2, class D2> -bool operator>(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);</ins> -<ins>template<class T1, class D1, class T2, class D2> -bool operator>=(const unique_ptr<T1, D1>& x, const unique_ptr<T2, D2>& y);</ins> -</pre></blockquote> - - - - - -<hr> -<h3><a name="1236"></a>1236. reserved identifiers in programs not using the library</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Sean Hunt <b>Opened:</b> 2009-10-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I wasn't sure whether to consider this a library or a language issue, -because the issue is I think it's incorrectly categorized as being part -of the library, so I thought I'd send a message to both of you and let -you sort it out. -</p> - -<p> -Most reserved identifiers are treated as unilaterally available to the -implementation, such as to implement language extensions, or provide -macros documenting its functionality. However, the requirements for -reserved identifers are in 17.6.4.3 [reserved.names], which are a -subsection of 17.6.4 [constraints]. 17.6.4.1 [constraints.overview] appears only to apply to "C++ programs -that use the facilities of the C++ standard library", meaning that, in -theory, all implementations are erroneous in having any non-standard -identifiers predefined for programs that do not, at some point, include -a standard library header. -</p> - -<p> -Furthermore, it's unclear whether the use of certain identifiers is UB -or results in an ill-formed program. In particular, 17.6.4.3.1 [macro.names] uses a "shall not", where [global.names] says that names are "reserved to the -implementation". 17.6.4.3 [reserved.names] seems only to cover the -instance of a name being described as "reserved", so are implementations -required to diagnose a program that performs, as an example, "<tt>#undef -get</tt>"? -</p> - -<p><i>[ -2009 Santa Cruz: -]</i></p> - - -<blockquote><p> -Move to NAD. There may in theory be multiple interpretations possible, -but there's no evidence that this causes any genuine problems or -uncertainty about what implementations are allowed to do. We do not -believe this rises to the level of a defect. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1239"></a>1239. Defect report</h3> -<p><b>Section:</b> 20.10.4.3 [meta.unary.prop] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2009-10-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#meta.unary.prop">active issues</a> in [meta.unary.prop].</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.unary.prop">issues</a> in [meta.unary.prop].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Table 43 defines a number of traits that yield true for arrays of class -types with the trait's property, but not arrays of other types with that -property. For example, <tt>has_trivial_default_constructor</tt>: -</p> - -<blockquote><p> -<tt>T</tt> is a trivial type (3.9) or a class type with a trivial default -constructor (12.1) or an array of such a class type. -</p></blockquote> - -<p><i>[ -2009-10 post-Santa Cruz: -]</i></p> - - -<blockquote> -<p> -An array of a trivial type is a trivial type. -</p> -<p> -Mark as Tentatively NAD Editorial. The wording is OK as is, -since an array of a trivial type is a trivial type, but the wording as -proposed might be clearer. -</p> -</blockquote> - - - -<p><b>Rationale:</b></p> -<p> -The wording is OK as is, since an array of a trivial type is a trivial type. -Project editor may wish to accept the suggested wording as editorial. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change all the traits in question following this pattern: -</p> - -<blockquote><p> -<tt>T</tt> is a trivial type (3.9) or a class type with a trivial default - constructor (12.1)<ins>,</ins> or an array of such a <del>class</del> type. -</p></blockquote> - -<p> -i.e., add a comma and delete a "class." -</p> - - - - - -<hr> -<h3><a name="1243"></a>1243. Missing <tt>operator+= (initializer_list<T>)</tt> for <tt>valarray</tt></h3> -<p><b>Section:</b> 26.6.2.7 [valarray.cassign] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2009-10-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#valarray.cassign">issues</a> in [valarray.cassign].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses JP 64</b></p> - -<p> -During the additions of <tt>initializer_list</tt> overloads -<tt>basic_string</tt> added: -</p> - -<blockquote><pre> -basic_string& operator+=(initializer_list<charT>); -</pre></blockquote> - -<p> -but -</p> - -<blockquote><pre> -valarray<T>& operator+= (initializer_list<T>); -</pre></blockquote> - -<p> -was not defined. -</p> - -<p><i>[ -Daniel adds on opening: -]</i></p> - - -<blockquote><p> -Recommend NAD. The <tt>operator+=</tt> overload of <tt>basic_string</tt> -behaves as-if calling <tt>append</tt>, which is completely different in -meaning as the existing <tt>operator+=</tt> overloads in -<tt>valarray</tt> which just sum the value or values to the existing -elements. The suggestion to add a corresponding append function to -<tt>valarray</tt> was not considered as appropriate and the request was -withdrawn (c++std-lib-24968). -</p></blockquote> - -<p><i>[ -2009-10 Santa Cruz: -]</i></p> - - -<blockquote><p> -Mark as NAD. Request has been withdrawn by NB. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add to 26.6.2.7 [valarray.cassign]: -</p> - -<blockquote><pre> -valarray<T>& operator+= (initializer_list<T>); -</pre></blockquote> - - - - - -<hr> -<h3><a name="1246"></a>1246. <tt>vector::resize()</tt> missing efficiency guarantee</h3> -<p><b>Section:</b> 23.3.6.3 [vector.capacity] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2009-10-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#vector.capacity">active issues</a> in [vector.capacity].</p> -<p><b>View all other</b> <a href="lwg-index.html#vector.capacity">issues</a> in [vector.capacity].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -If <tt>v</tt> is a <tt>vector</tt>, I think repeated calls to -<tt>v.resize( v.size() + 1 )</tt> should be amortized O(1), but it's not -clear that's true from the text of the standard: -</p> - -<blockquote><pre> -void resize(size_type sz); -</pre> -<blockquote><p> -<i>Effects:</i> If <tt>sz < size()</tt>, equivalent to <tt>erase(begin() + sz, end());</tt>. If -<tt>size() < sz</tt>, appends <tt>sz - size()</tt> default constructed elements to the -sequence. -</p></blockquote> -</blockquote> - -<p> -Seems to me if we used <tt>push_back</tt> instead of appends, we might be giving -the guarantee I'd like. Thoughts? -</p> - -<p><i>[ -2009-11-10 Howard adds: -]</i></p> - - -<blockquote><p> -Moved to Tentatively NAD after 5 positive votes on c++std-lib. Rationale added -below. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<p> -In 23.3.6.3 [vector.capacity]/10, change -</p> - -<blockquote><pre> -void resize(size_type sz); -</pre> -<blockquote><p> -<i>Effects:</i> If <tt>sz < size()</tt>, equivalent to <tt>erase(begin() + sz, end());</tt>. If -<tt>size() < sz</tt>, <del>appends <tt>sz - size()</tt> default constructed elements to the -sequence</del> -<ins>equivalent to <tt>sz - size()</tt> consecutive evaluations of <tt>push_back(T())</tt></ins>. -</p></blockquote> -</blockquote> - - - -<p><b>Rationale:</b></p> -<p> -The description in terms of <tt>push_back</tt> led some to believe that -one could expect the exact same growth pattern from both <tt>resize</tt> and -<tt>push_back</tt> (e.g.) which could lead to sub-optimal implementations. -Additionally, 23.3.6 [vector], p1 includes a statement that this container -"supports (amortized) constant time insert and erase operations at the end;", -therefore addressing the concern of this issue. -</p> - - - - - -<hr> -<h3><a name="1251"></a>1251. move constructing <tt>basic_stringbuf</tt></h3> -<p><b>Section:</b> 27.8.2.1 [stringbuf.cons] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2009-10-29 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#stringbuf.cons">issues</a> in [stringbuf.cons].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I just came across issue <a href="lwg-defects.html#1204">1204</a> -- Global permission to move, which -seems to address the concern raised by the example in c++std-lib-25030. -</p> -<p> -IIUC, the example violates the permission to assume that arguments -bound to rvalue references are unnamed temporaries granted to -implementations by the resolution of issue <a href="lwg-defects.html#1204">1204</a> - Global permission -to move. -</p> - -<p> -I.e., the <tt>ostringstream(ostringstream &&rhs)</tt> ctor can leave the <tt>rhs</tt> -pointers pointing to the newly constructed object's buffer just as -long as the dtor doesn't change or invalidate the buffer. The caller -may not make any assumptions about rhs after the move beyond it being -safe to destroy or reassign. -</p> - -<p> -So unless I misunderstood something, I still think the <tt>basic_stringbuf</tt> -move ctor is overspecified. Specifically, I think the third sentence -in the Effects clause and the last 6 bullets in the Postconditions -clause can, and IMO should, be stricken. -</p> - -<p><i>[ -2010-01-31 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - -<p><b>Rationale:</b></p> -<p> -The sense of 1251 appears to be that the <tt>basic_stringbuf</tt> move -constructor offers more guarantees than the minimum. This is true, and quite -correct. The additional words guarantee that the internal buffer has genuinely -transferred from one object to another, and further operations on the original -will not affect the buffer of the newly created object. This is a very -important guarantee, much as we see that a moved-from <tt>unique_ptr</tt> is -guaranteed to be empty. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Strike from 27.8.2.1 [stringbuf.cons]: -</p> - -<blockquote><pre> -basic_stringbuf(basic_stringbuf&& rhs); -</pre> -<blockquote> -<p> -<i>Effects:</i> Move constructs from the rvalue <tt>rhs</tt>. It is -implementation-defined whether the sequence pointers in <tt>*this</tt> -(<tt>eback()</tt>, <tt>gptr()</tt>, <tt>egptr()</tt>, <tt>pbase()</tt>, -<tt>pptr()</tt>, <tt>epptr()</tt>) obtain the values which <tt>rhs</tt> -had. <del>Whether they do or not, <tt>*this</tt> and <tt>rhs</tt> reference -separate buffers (if any at all) after the construction.</del> The openmode, -locale and any other state of <tt>rhs</tt> is also copied. -</p> - -<p> -<i>Postconditions:</i> Let <tt>rhs_p</tt> refer to the state of -<tt>rhs</tt> just prior to this construction and let <tt>rhs_a</tt> -referto the state of <tt>rhs</tt> just after this construction. -</p> -<ul> -<li> -<tt>str() == rhs_p.str()</tt> -</li> -<li> -<tt>gptr() - eback() == rhs_p.gptr() - rhs_p.eback()</tt> -</li> -<li> -<tt>egptr() - eback() == rhs_p.egptr() - rhs_p.eback()</tt> -</li> -<li> -<tt>pptr() - pbase() == rhs_p.pptr() - rhs_p.pbase()</tt> -</li> -<li> -<tt>epptr() - pbase() == rhs_p.epptr() - rhs_p.pbase()</tt> -</li> -<li><del> -if <tt>(eback()) eback() != rhs_a.eback()</tt> -</del></li> -<li><del> -if <tt>(gptr()) gptr() != rhs_a.gptr()</tt> -</del></li> -<li><del> -if <tt>(egptr()) egptr() != rhs_a.egptr()</tt> -</del></li> -<li><del> -if <tt>(pbase()) pbase() != rhs_a.pbase()</tt> -</del></li> -<li><del> -if <tt>(pptr()) pptr() != rhs_a.pptr()</tt> -</del></li> -<li><del> -if <tt>(epptr()) epptr() != rhs_a.epptr()</tt> -</del></li> -</ul> -</blockquote> -</blockquote> - - - - - - -<hr> -<h3><a name="1259"></a>1259. Should initializer-list constructors move elements?</h3> -<p><b>Section:</b> 23.2.3 [sequence.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Sean Hunt <b>Opened:</b> 2009-11-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#sequence.reqmts">issues</a> in [sequence.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -According to 23.2.3 [sequence.reqmts], <tt>X(il)</tt> is -equivalent to <tt>X(il.begin(), il.end())</tt>. Should it instead be -equivalent to <tt>X(move_iterator(il.begin()), -move_iterator(il.end()))</tt> so that needless copies are not made? This -doesn't seem ideal either - it may make more sense to provide two -overloads for the constructor, one for move and one for copy. -</p> - -<p><i>[ -2009-11-10 Howard adds: -]</i></p> - - -<blockquote><p> -I've moved this issue to Tentatively NAD after 5 positive votes on c++std-lib, -and added a rationale below. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - -<p><b>Rationale:</b></p> -<p> -There is no consensus at this time within EWG or CWG to make the -required language changes. Therefore this is not something that the LWG -can even consider. Should such language changes be made for a future -standard, no doubt there would need to be an accompanying library impact -survey. -</p> - - - - - -<hr> -<h3><a name="1263"></a>1263. missing <tt>swap</tt> overloads for <tt>regex</tt></h3> -<p><b>Section:</b> 28.4 [re.syn] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2009-11-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#re.syn">issues</a> in [re.syn].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p><b>Addresses: UK 314</b></p> - -<p> -In Message c++std-lib-25529, Alisdair writes: -</p> - -<blockquote> -<p> -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n3009.html#UK314">UK comment 314</a> -requests rvalue swap overloads in a couple of places they -were missed. -</p> - -<p> -We have in general reverted to the single swap signature taking lvalue -references, which could be seen as the alternative solution to -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n3009.html#UK314">UK 314</a>, -bringing consistency to the standard <g> -</p> - -<p> -Either way, I no longer expect to see any work to resolve this comment - -the work is complete and it should be either marked Rejected, or -Accepted with Modifications (namely, removing all other rvalue swaps!) -</p> -</blockquote> - -<p><i>[ -Moved to Tentatively NAD after 5 positive votes on c++std-lib. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p> -<p> -We have in general reverted to the single swap signature taking -lvalue references, which could be seen as the alternative solution to -UK 314, bringing consistency to the standard. -</p> - - - - - -<hr> -<h3><a name="1265"></a>1265. <tt>longjmp</tt> and destructors</h3> -<p><b>Section:</b> 18.10 [support.runtime] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Sean Hunt <b>Opened:</b> 2009-11-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#support.runtime">active issues</a> in [support.runtime].</p> -<p><b>View all other</b> <a href="lwg-index.html#support.runtime">issues</a> in [support.runtime].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -18.10 [support.runtime]/4 says that <tt>longjmp</tt> is undefined if -unwinding by the mechanism used by catch and throw would invoke any nontrivial -destructors. However, the text as written is rather vague, in particular when -dealing with <tt>catch(...)</tt>: -</p> - -<blockquote><pre> -void foo() { - jump_buf buf; - non_trivial_dtor n1; // 1 - if (!setjmp(buf)) { - non_trivial_dtor n2; // 2 - try { - longjmp(buf, 1); - } catch (...) { - } - } -} -</pre></blockquote> - -<p> -My interpretation of the meaning of 18.10 [support.runtime]/4 is that -declaration 2, but not 1, would cause the <tt>longjmp</tt> to be undefined -behavior. However, it's not entirely clear from the text. Arguably, replacing -the <tt>setjmp</tt> and <tt>longjmp</tt> with <tt>catch</tt> would still cause -the destructor for <tt>n1</tt> to be called after the unwinding, which would -lead to undefined behavior. This is clearly not an intended consequence of the -wording. However, it is probably still UB, as <tt>n1</tt> now has -"indeterminate" value, and running its destructor on <tt>foo</tt>'s exit will -cause Bad Things. -</p> - -<p> -Declarations 2 has a more interesting issue. The <tt>catch(...)</tt> muddles up -the definition that uses <tt>throw</tt> and <tt>catch</tt> - if -<tt>longjmp()</tt> were indeed a <tt>throw</tt>, control would never return to -the <tt>setjmp</tt>. As such, <tt>n2</tt>'s destructor wouldn't be called -(except by the argument for <tt>n1</tt>, which is that the destructor would be -called later as the frame was left in the normal control flow). -</p> - -<p> -I suggest that paragraph 4 of 18.10 [support.runtime] should be replaced -with the following, or something that reads better but has the same effect: -</p> - -<blockquote><p> -The function signature <tt>longjmp(jmp_buf jbuf, int val)</tt> has more -restricted behavior in this International Standard. A call to <tt>longjmp</tt> -has undefined behavior if any non-trivial destructors would be called were the -<tt>longjmp</tt> call replaced with a throw-expression whose nearest matching -handler were a (possibly imaginary) function-try-block on the function -containing the corresponding <tt>setjmp</tt> call. -</p></blockquote> - -<p><i>[ -2009-11-17 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Change 18.10 [support.runtime]/4: -</p> - -<blockquote><p> -The function signature <tt>longjmp(jmp_buf jbuf, int val)</tt> has more -restricted behavior in this International Standard. <del>A -<tt>setjmp</tt>/<tt>longjmp</tt> call pair has undefined behavior if replacing -the <tt>setjmp</tt> and <tt>longjmp</tt> by <tt>catch</tt> and <tt>throw</tt> -would invoke any non-trivial destructors for any automatic objects.</del> -<ins>A call to <tt>longjmp</tt> has undefined behavior if any non-trivial -destructors would be called were the <tt>longjmp</tt> call replaced with a -throw-expression whose nearest matching handler were a (possibly imaginary) -function-try-block on the function containing the corresponding <tt>setjmp</tt> -call.</ins> -</p></blockquote> - - -<p><b>Rationale:</b></p> -<p> -In the given example, it is clear that it is only <tt>n2</tt> and not -<tt>n1</tt> that is destroyed by the <tt>longjmp</tt>. -</p> -<p> -At this late stage in the standards process, we are focusing on issues that -impact users or implementers. Trying to rewrite complex wording just for the -sake of improved clarity is likely to do more harm than good. -</p> - - - - - -<hr> -<h3><a name="1296"></a>1296. <tt>map</tt> and <tt>multimap value_compare</tt> overspecified</h3> -<p><b>Section:</b> 23.4.4 [map] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2009-12-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#map">issues</a> in [map].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The container class templates <tt>map</tt> and <tt>multimap</tt> both contain a -nested type called <tt>value_compare</tt>, that is used to compare the -<tt>value_type pair</tt> elements, an adaptor of the user-supplied comparison -function-like object. -</p> - -<p> -I believe these types are over-specified, as we require a distinct type for each -template, even though the allocator plays no part in the comparator, and -<tt>map</tt> and <tt>multimap value_compare</tt> classes could easily be shared. - The benefits are similar to the SCARY iterator proposal (although on a much -smaller scale!) but unlike SCARY, this is not a QoI issue today but actively -prohibited. -</p> - -<p> -If the <tt>value_compare</tt> classes were marked 'exposition only', a vendor -would be free to experiment with implementations that do not produce so many -template instantiations with negligible impact on conforming programs. (There -is a minor risk that programs could no longer portably overload functions taking -<tt>value_compare</tt> types. This scenario is extremely unlikely outside -conformance suites.) -</p> - -<p> -(Note that there are no similar problems for unordered maps, nor any of the set -variants) -</p> - -<p><i>[ -2010-01-31 Moved to Tentatively NAD after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - -<p><b>Rationale:</b></p> -<p> -The <tt>value_compare</tt> specification is an unfortunate bit from the past -that we have to live with. Fortunately vendors can work around the problems -mentioned in this issue. -</p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -p2 23.4.4 [map]: -Above the declaration of class <tt>value_compare</tt> in the map synopsis, add: -</p> - -<blockquote><pre> -template <class Key, class T, class Compare = less<Key>, - class Allocator = allocator<pair<const Key, T> > > -class map { -public: - // types: - ... - <ins>// exposition only.</ins> - class value_compare - : public binary_function<value_type,value_type,bool> { - ... -</pre></blockquote> - - - -<p> -p2 23.4.5 [multimap]: -Above the declaration of class <tt>value_compare</tt> in the map synopsis, add: -</p> - -<blockquote><pre> -template <class Key, class T, class Compare = less<Key>, - class Allocator = allocator<pair<const Key, T> > > -class multimap { -public: - // types: - ... - <ins>// exposition only.</ins> - class value_compare - : public binary_function<value_type,value_type,bool> { - ... -</pre></blockquote> - - - - - -<hr> -<h3><a name="1301"></a>1301. <tt>clear()</tt> and assignment</h3> -<p><b>Section:</b> 23.2.3 [sequence.reqmts] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Nicolai Josuttis <b>Opened:</b> 2010-01-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#sequence.reqmts">issues</a> in [sequence.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I propose that <tt>clear()</tt> be defined to be equivalent to -<tt>erase(begin(),end())</tt> except not using copy or move of elements. -</p> - -<blockquote> -<p> -To: C++ libraries mailing list<br/> -Message c++std-lib-26465 -</p> - -<p> -and specifiying as post: <tt>size()==0</tt> might also not be appropriate -because forward-Lists provide no <tt>size()</tt>, this it should be: -post: <tt>empty()==true</tt> -</p> - -<p> -Bjarne Stroustrup schrieb/wrote: -</p> - -<blockquote> -<p> -To: C++ libraries mailing list<br/> -Message c++std-lib-26458 -</p> - -<p> -in table 94 we define <tt>clear()</tt> as: -</p> - -<blockquote><pre> -a.clear() void erase(begin(), end()) -post: size() == 0 -</pre></blockquote> - -<p> -Now <tt>erase</tt> requires assignment (<tt>MoveAssignable</tt>) which makes -sense if we have to move an element, but why should that be required from -<tt>clear()</tt> where all elements are destroyed? -</p> -</blockquote> -</blockquote> - -<p><i>[ -2010-01-23 Alisdiar provides wording. -]</i></p> - - -<p><i>[ -2010-01-30 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]</i></p> - - -<p><i>[ -2010-01-30 Daniel opens: -]</i></p> - - -<blockquote> -<p> -First, I read the newly proposed spec for <tt>clear()</tt> that it does in -general <em>not</em> invalidate a previous past-the-end iterator value, but -<tt>deque</tt> says in 23.3.3.4 [deque.modifiers] for the semantics of -<tt>erase</tt> that erasures at the end will invalidate the past-the-end -iterator. With removal of a direct binding between <tt>clear()</tt> and -<tt>erase()</tt> there seem to be some fixes necessary. One way to fix that -would be to mention in Table 94 that this "may also invalidate the past-the-end -iterator" and then to mention for all specific containers where this does not -happen, the exception, [1] e.g. in <tt>std::vector</tt>. <tt>std::vector</tt> -has no own specification of <tt>clear()</tt> and one aspect of the closed issue -<a href="lwg-closed.html#1102">1102</a> was to realize just that (indirectly via <tt>erase</tt>). IMO -we should now add an extra specification for <tt>clear()</tt>. Btw.: -<tt>std::vector::erase</tt> reads to me that it would invalidate previous -past-the-end values (and that seems correct in general). -</p> -<p> -Before I will provide explicit wording, I would like to -discuss these points. -</p> - -<p> -[1] <tt>std::list</tt> does fortunately specify that clear does not invalidate -the past-the-end iterator. -</p> -</blockquote> - -<p><i>[ -2010-02-08 Moved to Tentatively NAD Editorial after 5 positive votes on c++std-lib. -Rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -Solved as proposed by LWG <a href="lwg-defects.html#704">704</a>. -</p> - - -<p><b>Proposed resolution:</b></p> - -<p> -Change 23.2.1 [container.requirements.general]/10: -</p> - -<blockquote> -<p> -Unless otherwise specified (see 23.2.4.1, 23.2.5.1, 23.3.2.3, and 23.3.6.4) all -container types defined in this Clause meet the following additional -requirements: -</p> - -<ul> -<li> -.. -</li> - -<li> -no <tt>erase()</tt>, <ins><tt>clear()</tt>,</ins> <tt>pop_back()</tt> or -<tt>pop_front()</tt> function throws an exception. -</li> - -<li> -... -</li> -</ul> - -</blockquote> - -<p> -Replace the following words from Table 94 — Sequence container -requirements (in addition to container) in 23.2.3 [sequence.reqmts]: -</p> - -<blockquote> -<table border="1"> -<caption>Table 94 — Sequence container requirements (in addition to -container)</caption> -<tr> -<th>Expression</th> -<th>Return type</th> -<th>Assertion/note<br/>pre-/post-condition</th> -</tr> - -<tr> -<td><tt>a.clear()</tt></td> -<td><tt>void</tt></td> -<td><del><tt>erase(begin(), end())</tt></del><br/> -<ins>Destroys all elements in the container a. Invalidates all references, -pointers, and iterators referring to the elements of <tt>a</tt> and may -invalidate the past-the-end iterator.</ins><br/> -post: <tt><del>size() == 0</del> <ins>a.empty() == true</ins></tt>. </td> -</tr> -</table> -</blockquote> - -<p> -Add a new paragraph after 23.3.4.5 [forwardlist.modifiers]/23: -</p> - -<blockquote><pre> -void clear(); -</pre> - -<blockquote> -<p> -23 <i>Effects:</i> Erases all elements in the range <tt>[begin(),end())</tt>. -</p> -<p><ins> -<i>Remarks:</i> Does not invalidate past-the-end iterators. -</ins></p> -</blockquote> -</blockquote> - - - - - - -<hr> -<h3><a name="1302"></a>1302. different <tt>emplace</tt> semantics for sequence and associated containers</h3> -<p><b>Section:</b> 23.2.4 [associative.reqmts], 23.2.5 [unord.req] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nicolai Josuttis <b>Opened:</b> 2010-01-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#associative.reqmts">active issues</a> in [associative.reqmts].</p> -<p><b>View all other</b> <a href="lwg-index.html#associative.reqmts">issues</a> in [associative.reqmts].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -According to the new naming scheme introduced with -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2680.pdf">N2680</a> -</p> - -<blockquote><pre> -vector<T> v; -v.emplace(v.begin(),x,y,z) -</pre></blockquote> - -<p> -now has a different semantics than -</p> - -<blockquote><pre> -set<T> s; -s.emplace(s.begin(),x,y,z); -</pre></blockquote> - -<p> -While the version for <tt>vector</tt>s takes the first argument as position and -the remaining for construction, the version for <tt>set</tt>s takes all -arguments for construction. -</p> - -<p> -IMO, this is a serious design mistake for a couple of reasons: -</p> - -<ul> -<li> -<p> -First, in principle, all STL member functions should have the same behavior with -the same member function to avoid confusion and allow to write proper generic -code. -</p> -<p> -In fact, when I write the following simple function template: -</p> -<blockquote><pre> -template <typename T> -void doEmplace (T& cont) -{ - cont.emplace(cont.begin(),"nico","josuttis",42); -} -</pre></blockquote> -<p> -the semantics depends on the type of the container. -</p> -</li> -<li> -<p> -In addition, I also guess using the name <tt>emplace_hint()</tt> instead of -<tt>emplace()</tt> for associative containers is a design mistake. According to -my knowledge, it was a design goal of the original STL to provide ONE -<tt>insert</tt> function, which works for ALL containers. This was -<tt>insert(pos,val)</tt>. -</p> -<p> -The trick to declare <tt>pos</tt> as a hint, allowed that we could implement a -generic <tt>insert</tt> for all containers. Now, with the new <tt>emplace</tt> -naming scheme, this trick is gone for the new kind of insertion. -</p> -</li> -</ul> - -<p> -I consider this to be a serious design penalty because once this -is specified we can't fix that without breaking backward compatibility. -</p> - -<p> -However, we have two choices for a fix: -</p> - -<ul> -<li> -rename <tt>emplace_hint(pos,val)</tt> for associative containers back to -<tt>emplace(pos,val)</tt>. However to avoid the overloading problems, we also -have to rename the existing <tt>emplace(val)</tt> functions to something else (I -don't have a good name here at hand). -</li> -<li> -Keep <tt>emplace(val)</tt> for associative containers as it is, but rename -<tt>emplace(pos,val)</tt> for sequence containers and -<tt>emplace_hint(pos,val)</tt> to something like <tt>emplace_at(pos,val)</tt>, -declaring that <tt>pos</tt> is a hint for associative containers. -</li> -</ul> - -<p><i>[ -2010 Pittsburgh: Moved to NAD, rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -There was no consensus to make this change. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> In 23.2.5 [unord.req], change: </p> -<blockquote> - <table border="1"> - <caption>Table 96 — Associative container requirements (in addition to - container)</caption> - <tr> - <th>expression</th> - <th>Return type</th> - <th>Assertion/note pre-/post-condition</th> - <th>Post-condition</th> - </tr> - <tr> - <td colspan="4">...</td> - </tr> - <tr> - <td><tt>a_uniq.emplace<ins>_value</ins>(args)</tt></td> - <td><tt>pair<iterator, bool></tt></td> - <td>inserts a T object t constructed with std::forward<Args>(args)...<br/> - if and only if there is no element in the container with key equivalent - to the key of t.<br/> - The bool component of the returned pair is true if and only if the insertion - takes place, and the iterator component of the pair points to the element - with key equivalent to the key of t.</td> - <td>logarithmic</td> - </tr> - <tr> - <td><tt>a_eq.emplace<ins>_value</ins>(args)</tt></td> - <td><tt>iterator</tt></td> - <td>inserts a T object t constructed with std::forward<Args>(args)... - and returns the iterator pointing to the newly inserted element.</td> - <td>logarithmic</td> - </tr> - <tr> - <td><tt>a.emplace<del>_hint</del>(p,args)</tt></td> - <td><tt>iterator</tt></td> - <td>equivalent to - <tt>a.emplace<ins>_value</ins>(std::forward<Args>(args)...)</tt>. - Return value is an iterator pointing to the element with the key - equivalent to the newly inserted element. The const_iterator p is a hint - pointing to where the search should start. Implementations are permitted - to ignore the hint.</td> <td>logarithmic in general, but amortized - constant if the element is inserted right after p</td> - </tr> - <tr> - <td colspan="4">... </td> - </tr> - </table> - -</blockquote> -<p> In 23.2.5 [unord.req], change: </p> -<blockquote> - <table border="1"> - <caption>Table 98 — Unordered associative container requirements (in - addition to container)</caption> - <tr> - <th>expression</th> - <th>Return type</th> - <th>Assertion/note pre-/post-condition</th> - <th>Post-condition</th> - </tr> - <tr> - <td colspan="4">...</td> - </tr> - <tr> - <td><tt>a_uniq.emplace<ins>_value</ins>(args)</tt></td> - <td><tt>pair<iterator, bool></tt></td> - <td>inserts a <tt>T</tt> object <tt>t</tt> constructed with <tt>std::forward<Args>(args)...</tt> if - and only if there is no element in the container with key equivalent to - the key of <tt>t</tt>. The bool component of the returned pair is true if and only - if the insertion takes place, and the iterator component of the pair points - to the element with key equivalent to the key of t.</td> - <td>Average case O(1), worst case O(a_uniq.size()).</td> - </tr> - <tr> - <td><tt>a_eq.emplace<ins>_value</ins>(args)</tt></td> - <td><tt>iterator</tt></td> - <td>inserts a T object t constructed with std::forward<Args>(args)... - and returns the iterator pointing to the newly inserted element.</td> - <td>Average case O(1), worst case O(a_eq.size()).</td> - </tr> - <tr> - <td><tt>a.emplace<del>_hint</del>(p,args)</tt></td> - <td><tt>iterator</tt></td> - <td>equivalent to - <tt>a.emplace<ins>_value</ins>(std::forward<Args>(args)...)</tt>. - Return value is an iterator pointing to the element with the key - equivalent to the newly inserted element. The const_iterator p is a hint - pointing to where the search should start. Implementations are permitted - to ignore the hint.</td> <td>Average case O(1), worst case - O(a.size()).</td> - </tr> - <tr> - <td colspan="4">... </td> - </tr> - </table> -</blockquote> - -<p> -In 23.4.4 [map], 23.4.6 [set], 23.5.4 [unord.map], 23.5.6 [unord.set], change: -</p> -<blockquote> - <p><i>// modifiers:</i><br/> - <tt>template <class... Args> pair<iterator, bool> emplace<ins>_value</ins>(Args&&... - args);<br/> - template <class... Args> iterator emplace<del>_hint</del>(const_iterator - position, Args&&... args);</tt></p> -</blockquote> - -<p> -In 23.4.5 [multimap], 23.4.7 [multiset], 23.5.5 [unord.multimap], 23.5.7 [unord.multiset], change: -</p> -<blockquote> - <p><i>// modifiers:<br/></i><tt>template <class... Args> iterator emplace<ins>_value</ins>(Args&&... - args);<br/> - template <class... Args> iterator emplace<del>_hint</del>(const_iterator position, - Args&&... args);<br/> - </tt> </p> -</blockquote> - - - - - -<hr> -<h3><a name="1308"></a>1308. Concerns about <tt>initializer_list</tt> overloads of <tt>min</tt>, -<tt>max</tt>, and <tt>minmax</tt></h3> -<p><b>Section:</b> 25.4.7 [alg.min.max] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Niels Dekker <b>Opened:</b> 2010-02-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.min.max">issues</a> in [alg.min.max].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In San Francisco, June 2008, -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2722.pdf">N2722</a> -was adopted, replacing the variadic templates <tt>min</tt>, <tt>max</tt>, and -<tt>minmax</tt> by overloads that have an <tt>initializer_list<T></tt> -parameter. The paper showed benchmark results wherein <tt>initializer_list</tt> -versions of <tt>min</tt> appeared to outperform the corresponding variadic -template. Unfortunately, in October 2009 a very serious error was detected in -the benchmark. (<a href="http://accu.org/cgi-bin/wg21/message?wg=lib&msg=25210">c++std-lib-25210</a>). -In fact, an <tt>initializer_list<T></tt> version of <tt>min</tt> often -appears to perform <i>worse</i> than the corresponding variadic template, -especially when <tt>T</tt> has an expensive copy constructor -(<a href="http://accu.org/cgi-bin/wg21/message?wg=lib&msg=25253">c++std-lib-25253</a>, -<a href="http://www.xs4all.nl/~nd/dekkerware/issues/n2772_fix">http://www.xs4all.nl/~nd/dekkerware/issues/n2772_fix</a>). -</p> -<p> -IMO, the biggest problem of the <tt>initializer_list</tt> overloads is that they -pass and return <tt>T</tt> objects <i>by value</i>. Which has the following -consequences: -</p> - -<ol> -<li> -They require that <tt>T</tt> is <tt>CopyConstructible</tt>. IMO that is too much of a -constraint for a generic, general purpose function like -<tt>std::min<T></tt>. -</li> -<li> -They potentially throw an exception, even if <tt>T</tt>'s less-than-operator -throws nothing. (And of course, less-than typically throws nothing.) -</li> -<li> -They are inconsistent with C++03 <tt>std::min</tt> and <tt>std::max</tt>. -Consider the subtle difference between <tt>const T& c1 = min(a,b);</tt> and -<tt>const T& c2 = min({a,b});</tt> -(<a href="http://accu.org/cgi-bin/wg21/message?wg=lib&msg=25265">c++std-lib-25265</a>) -</li> -<li> -They do not conveniently support use cases that need to have a reference to the -minimum or maximum object <i>itself</i>, rather than just a copy. -</li> -<li> -They potentially perform badly: possibly <i>O(n)</i>, when the arguments -themselves have a size of <i>n</i>. -</li> -</ol> - -<p> -In the future, this problem might be solvable by using an -<tt>initializer_list</tt> of <i>const references</i>, instead: -</p> -<blockquote><pre> -const T& min(initializer_list<const T&>); -const T& max(initializer_list<const T&>); -pair<const T&, const T&> minmax(initializer_list<const T&>); -</pre></blockquote> - -<p> -It is unlikely that C++0x will support <tt>initializer_list<const T&></tt>, -but technically it seems possible to add such a language -feature after C++0x -(<a href="http://accu.org/cgi-bin/wg21/message?wg=core&msg=15428">c++std-core-15428</a>). -</p> -<p> -Variadic templates of <tt>min</tt>, <tt>max</tt>, and <tt>minmax</tt>, as -proposed by -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2551.pdf">N2551</a> -(Sylvain Pion), do have some other advantages over <tt>initializer_list</tt> -overloads: -</p> -<ol> -<li> -It is likely that those variadic templates can be declared <tt>constexpr</tt>, -now that -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n3006.html#991"> -CWG issue #991</a> is in drafting status. -</li> -<li> -They provide complete compile-time protection against accidentally passing zero -arguments. -</li> -</ol> - -<p> -Unfortunately, the variadic templates of <tt>min</tt>, <tt>max</tt>, and -<tt>minmax</tt> may still need further improvement, before having them in the -Standard Library. Especially the optional <tt>Compare</tt> parameter appears to -be a concern. So for this moment I recommend to keep both versions out of C++0x, -and postpone further discussion until after C++0x. -</p> - -<p><i>[ -2010 Pittsburgh: Discussed and the LWG still prefers the initializer list -solution of -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2772.pdf">N2772</a>. -]</i></p> - - - - -<p><b>Rationale:</b></p><p> -We prefer the solution of -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2772.pdf">N2772</a> -which will be reapplied. -</p> - -<p><b>Proposed resolution:</b></p> -<p> -Remove both variadic templates and <tt>initializer_list</tt> overloads of -<tt>min</tt>, <tt>max</tt>, and <tt>minmax</tt> from the synopsis in -25.1 [algorithms.general] and from 25.4.7 [alg.min.max]. -</p> - -<blockquote> -<p><i>[ -Note: This proposed resolution will resolve LWG <a href="lwg-closed.html#915">915</a> as NAD. -]</i></p> - -</blockquote> - - - - - -<hr> -<h3><a name="1313"></a>1313. Seed sequence's param function not useful for pure output iterator</h3> -<p><b>Section:</b> 26.5.7.1 [rand.util.seedseq] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2010-02-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.util.seedseq">issues</a> in [rand.util.seedseq].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The Seed sequence requirements (26.5.1.2 [rand.req.seedseq]) require the -existence of a member function -</p> - -<blockquote><pre> -template<typename OutputIterator> -void param(OutputIterator ob); -</pre></blockquote> - -<p> -The fact that this function returns <tt>void</tt> instead of the value of -<tt>ob</tt> after accepting the sequence data leads to the same problem as in -issue <a href="lwg-defects.html#865">865</a> - In case of pure output iterators there is no way to -serialize further data into that data sink. -</p> - -<p><i>[ -2010-02-07 Howard adds: -]</i></p> - - -<blockquote><p> -At the time this issue was opened, the suggested changes are with respect to an -anticipated draft which does not yet exist. -</p></blockquote> - -<p><i>[ -2010 Pittsburgh: -]</i></p> - - -<blockquote><p> -No technical counterarguments, but it is simply too late in the process -to make this change at this point. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -<p> -In Table 109 — Seed sequence requirements, expression "<tt>r.param(ob)</tt>" -change the<br/> -Return type entry: -</p> - -<blockquote><pre> -<del>void</del><ins>OutputIterator</ins> -</pre></blockquote> -</li> - -<li> -<p> -In 26.5.7.1 [rand.util.seedseq], class seed_seq synopsis change -</p> - -<blockquote><pre> -template<class OutputIterator> -<del>void</del><ins>OutputIterator</ins> param(OutputIterator dest) const; -</pre></blockquote> -</li> - -</ol> - - - - - - -<hr> -<h3><a name="1314"></a>1314. <tt>NULL</tt> and <tt>nullptr</tt></h3> -<p><b>Section:</b> 18.2 [support.types] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Sean Hunt <b>Opened:</b> 2010-02-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#support.types">issues</a> in [support.types].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Currently, the 18.2 [support.types]/3 allows <tt>NULL</tt> to be any -null pointer constant. The footnote marks that 0 or 0L might be appropriate. -However, this definition also allows the implementation to define <tt>NULL</tt> -to be <tt>nullptr</tt>. This may lead to overload and conversion issues more -serious than with the C++98 version: -</p> - -<blockquote><pre> -void f(void*); -void f(int); - -void g() -{ - // calls f(int) if NULL is integral - // calls f(void*) if NULL is nullptr - f(NULL); -} -</pre></blockquote> - -<p> -Possible resolutions: -</p> -<ul> -<li> -Forbid <tt>NULL</tt> from being <tt>nullptr</tt> -</li> -<li> -Require <tt>NULL</tt> to be <tt>nullptr</tt> -</li> -<li> -Leave it as is -</li> -</ul> - -<p> -Making <tt>NULL</tt> <tt>nullptr</tt> would improve code correctness, and -breaking backwards compatibility shouldn't be a huge concern as <tt>NULL</tt> -shouldn't be used except as a null pointer constant anyways. -</p> - -<p><i>[ -2010-02-10 Chris provided wording. -]</i></p> - - -<p><i>[ -2010 Pittsburgh: Moved to NAD, rationale added below. -]</i></p> - - - - -<p><b>Rationale:</b></p> -<p> -The LWG discussed the proposed resolution and several other options. There was -no concensus to make this or any other changes. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -18.2 [support.types] -</p> - -<blockquote> -<p> -3 The macro <tt>NULL</tt> <ins>is defined to be <tt>nullptr</tt>.</ins> <del>is -an implementation-defined C++ null pointer constant in this International -Standard (4.10).<sup>196</sup></del> -</p> - -<p><del> -196) Possible definitions include <tt>0</tt> and <tt>0L</tt>, but not -<tt>(void*)0</tt>. -</del></p> -</blockquote> - -<p> -20.7.13 [c.malloc] -</p> - -<blockquote><p> -7 The contents are the same as the Standard C library header -<tt><string.h></tt>, with the change to <tt>memchr()</tt> specified in -21.6 <ins>and the macro <tt>NULL</tt> defined to be <tt>nullptr</tt></ins>. -</p></blockquote> - - -<p> -20.12.8 [date.time] -</p> - -<blockquote><p> -2 The contents are the same as the Standard C library header -<tt><time.h></tt><del>.</del><sup>232</sup> <ins>except the macro -<tt>NULL</tt>, which is defined to be <tt>nullptr</tt>.</ins> The functions -<tt>asctime</tt>, <tt>ctime</tt>, <tt>gmtime</tt>, and <tt>localtime</tt> are -not required to avoid data races (17.6.4.8). -</p></blockquote> - - -<p> -22.6 [c.locales] -</p> - -<blockquote><p> -2 The contents are the same as the Standard C library header -<tt><locale.h></tt> <ins>except the macro <tt>NULL</tt>, which is defined -to be <tt>nullptr</tt></ins>. -</p></blockquote> - -<p> -C.5.2.4 [diff.null] -</p> - -<blockquote><p> -1 The macro <tt>NULL</tt>, defined in any of <tt><clocale></tt>, -<tt><cstddef></tt>, <tt><cstdio></tt>, <tt><cstdlib></tt>, -<tt><cstring></tt>, <tt><ctime></tt>, or <tt><cwchar></tt>, is -<ins>nullptr</ins> <del>an implementation-defined C++ null pointer constant in -this International Standard (18.2).</del> -</p></blockquote> - - - - - - -<hr> -<h3><a name="1315"></a>1315. return type of <tt>async</tt></h3> -<p><b>Section:</b> 30.6.8 [futures.async] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Jonathan Wakely <b>Opened:</b> 2009-02-09 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.async">issues</a> in [futures.async].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Both overloads of <tt>async</tt> return <tt>future<typename -F::result_type></tt> which requires that <tt>F</tt> has a nested type. This -prevents <tt>async</tt> being used with function pointers and makes the example -in 30.6.8 [futures.async] invalid. I believe this is unintentional. -</p> - -<p> -The proposed resolution also addresses editorial issues with the -<tt>launch_policy</tt> function parameter. -</p> - -<p> -For the first overload it is not sufficient to return <tt>future<typename -result_of<F(ArgTypes...)>::type></tt>. Calling <tt>async(launch::xxx, -foo, bar)</tt> performs argument deduction on both <tt>async</tt> overloads, -which for the first overload attempts to instantiate <tt>result_of<launch(F, -ArgTypes...)></tt>, which is invalid. SFINAE must be used to prevent that. -</p> - -<p><i>[ -2010-02-12 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]</i></p> - - -<p><i>[ -2010-02-12 Daniel opens: -]</i></p> - - -<blockquote> -<p> -[..] if <tt>decay<F>::type</tt> is of type <tt>std::launch</tt>. -</p> -<p> -or -</p> -<p> -[..] if <tt>remove_cv<remove_reference<F>::type>::type</tt> is of -type <tt>std::launch</tt>. -</p> - -<p> -The latter is the more specific form, but the former is equivalent to -the latter for all cases that can occur here. I suggest to use the -former for simplicity, but expect that implementations can effectively -use the latter. - -</p> -</blockquote> - -<p><i>[ -2010-02-12 Moved to Tentatively Ready after 5 positive votes on c++std-lib. -]</i></p> - - -<p><i>[ -2010 Pittsburgh: -]</i></p> - - -<blockquote><p> -Moved to NAD Editorial. Rationale added below. -</p></blockquote> - - - -<p><b>Rationale:</b></p> -<p> -Solved by N3058. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In 30.6.1 [futures.overview] paragraph 1: -</p> - -<blockquote><pre> -template <class F, class... Args> - <del>future<typename F::result_type></del> - <ins>future<typename result_of<F(Args...)>::type></ins> - async(F&& f, Args&&... args); -template <class F, class... Args> - <del>future<typename F::result_type></del> - <ins>future<typename result_of<F(Args...)>::type></ins> - async(launch policy, F&& f, Args&&... args); -</pre></blockquote> - -<p> -In 30.6.8 [futures.async] before paragraph 1 -</p> - -<blockquote><pre> -template <class F, class... Args> - <del>future<typename F::result_type></del> - <ins>future<typename result_of<F(Args...)>::type></ins> - async(F&& f, Args&&... args); -template <class F, class... Args> - <del>future<typename F::result_type></del> - <ins>future<typename result_of<F(Args...)>::type></ins> - async(launch policy, F&& f, Args&&... args); -</pre> -<blockquote> -<p>...</p> -<p><ins> -<i>Remarks:</i> The first signature shall not participate in overload resolution -if <tt>decay<F>::type</tt> is <tt>std::launch</tt>. -</ins></p> -</blockquote> -</blockquote> - - - - - - -<hr> -<h3><a name="1318"></a>1318. N2982 removes previous allocator capabilities</h3> -<p><b>Section:</b> 20.7.8.1 [allocator.traits.types] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2010-02-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-closed.html#1375">1375</a></p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-87</b></p> -<p> -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2982.pdf">N2982</a> -says that containers should have a nested typedef that defines their -<tt>reference_type</tt> as <tt>value_type&</tt>; the previous -standard deferred to the allocator to define its -<tt>reference_type</tt>, and containers simply passed the allocator's -typedef on. This change is a mistake. Allocators should define both a -<tt>pointer</tt> type and a <tt>reference</tt> type. That's essential -for their original purpose, which was to make different memory models -transparent. If an allocator defines a <tt>pointer</tt> type that isn't -compatible with a normal pointer it also has to define a corresponding -<tt>reference</tt> type. For example (and please forgive a Windows-ism), -if an allocator's pointer is <tt>T __far*</tt>, then it's -<tt>reference</tt> has to be <tt>T __far&</tt>. Otherwise everything -crashes (under the hood, references are pointers and have to have the -same memory access mechanics). Extensions such as this for more general -memory models were explicitly encouraged by C++03, and the allocator's -<tt>pointer</tt> and <tt>reference</tt> typedefs were the hooks for such -extensions. Removing the allocator's <tt>reference</tt> and -<tt>const_reference</tt> typedefs makes those extensions unimplementable -and breaks existing implementations that rely on those hooks. -</p> - -<p><i>[ -2010-02-25 Alisdair adds: -]</i></p> - - -<blockquote> -<p> -<tt>vector<bool>::reference</tt> is a nested class, and not a typedef. It -should be removed from the list of containers when this change is made. -</p> - -<p> -In general, I am uncomfortable placing this reference requirement on each -container, as I would prefer to require: -</p> - -<blockquote><pre> -is_same<Container::reference, Container::iterator::reference> -</pre></blockquote> - -<p> -This distinction is important, if we intend to support proxy iterators. The -iterator paper in the pre-Pittsburgh mailing -(<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3046.html">N3046</a>) -does <em>not</em> make this proposal, but organises clause 24 in such a way this -will be much easier to specify. -</p> - -<p> -The changes to clause 20 remain important for all the reasons Pete highlights. -</p> -</blockquote> - -<p><i>[ -2010 Batavia -]</i></p> - - -<p> -Removed <tt>vector</tt> from list of templates that should be adjusted as of meeting outcome. -</p> - -<p><i>[ -2010 post-Batavia -]</i></p> - - -<p> -Replaced <tt>vector<bool></tt> reference by <tt>vector</tt> reference because of misinterpreting meeting typo. -Additional corrected numbering in P/R to N3225 wording. -</p> - -<p><i>[ -2010-12-06 Daniel reopens -]</i></p> - - -<p> -Unfortunately, the current P/R is defective for several reasons: -</p> -<ol> -<li> Table 43 — Descriptive variable definitions still contains three -references to <tt>T&</tt>, namely in: -<blockquote> -<table border="1"> -<tr> -<td> -<tt>t</tt> -</td> -<td>a value of type <tt>const T&</tt></td> -</tr> -<tr> -<td> -<tt>r</tt> -</td> -<td>a value of type <tt>T&</tt> obtained by the expression <tt>*p</tt></td> -</tr> -<tr> -<td> -<tt>s</tt> -</td> -<td>a value of type <tt>const T&</tt> obtained by the expression <tt>*q</tt> -or by conversion from a value <tt>r</tt></td> -</tr> -</table> -</blockquote> -Especially the second and third items are misses in the 1318 P/R, -e.g. in N2723 or in C++03 these were referring -to <tt>X::reference</tt> and <tt>X::const_reference</tt>, resp. -None of them is referenced anywhere in the allocator requirements -table: <tt>r</tt> and <tt>s</tt> where historically needed to -define the expressions <tt>a.address(r)</tt> and <tt>a.address(s)</tt> which are gone now, -and <tt>t</tt> was needed to define the expression <tt>a.construct(p, t)</tt> which has been -replaced by <tt>a.construct(p,args)</tt>. -<p/> -The easiest fix seems to be to remove all three rows from Table 43. -</li> -<li> -Further-on, the current P/R suggests to replace the the current -definitions of the adaptor classes -<blockquote><pre> -stack -priority_queue -queue -</pre></blockquote> -similar to the other container types, i.e. to define <tt>reference</tt> and -<tt>const_reference</tt> now as -<blockquote><pre> -typedef typename allocator_traits<Allocator>::reference reference; -typedef typename allocator_traits<Allocator>::const_reference const_reference; -</pre></blockquote> -This would not only be an ill-formed definition (because there is no name -<tt>Allocator</tt> in scope), but it would also introduce a breakage compared to C++03, -where these definitions where already referring to the definition of the wrapped -containers. So, the adaptor class templates should be removed from the current list. -</li> -<li> -Then the current P/R wording leads to one further unexpected and unwanted change due to -the general formular used: <tt>match_result::reference</tt> is currently defined as -<blockquote><pre> -typedef const_reference reference; -</pre></blockquote> -because it is an <em>immutable</em> container (And we had this definition -already in N2723). The application of the rule would change this silently. -</li> -<li> -Finally the suggested wording for the <tt>unordered_</tt> containers is incomplete. -The reason is a current inconsistency between these containers and the rest: While -normally the definition of the pointer types is -<blockquote><pre> -typedef typename allocator_traits<Allocator>::pointer pointer; -typedef typename allocator_traits<Allocator>::const_pointer const_pointer; -</pre></blockquote> -for the unordered containers they are -<blockquote><pre> -typedef typename allocator_type::pointer pointer; -typedef typename allocator_type::const_pointer const_pointer; -</pre></blockquote> -These definitions are <em>not</em> equivalent, because allocators are no longer -required to define typedefs <tt>pointer</tt> and <tt>const_pointer</tt>, the -<tt>allocator_traits</tt> were invented as a further indirection to cope -with that. I.e. for the unordered containers we need to bring both the definition -of references <em>and</em> pointers in sync. -</li> -</ol> - -<p><i>[ -2011-02-23 Daniel updates the proposed wording with support from Pablo -]</i></p> - - -<p>The update attempts to fix the backward-compatibility problem that we have -introduced by ignoring the C++03 member function overloads <tt>address</tt> -of allocator types in C++0x completely. The resolution attempts to fix that -by adding these functions as optional members of allocators that are considered -first before falling back to <tt>pointer_traits::pointer_to</tt>. This still -allows us to remove the unused symbol <tt>t</tt> from the table, but we adapt -the symbols <tt>r</tt> and <tt>s</tt> to purely refer to the typenames -<tt>reference</tt> and <tt>const_reference</tt>.</p> - -<p><i>[2011-03-06 Daniel adapts numbering to N3242]</i></p> - - -<p><i>[2011-03-11 Daniel removes <tt>noexcept</tt> specifiers from <tt>address</tt> functions]</i></p> - - -<p><i>[2011-03-12 Further wording improvements by Daniel and Pablo]</i></p> - - -<p><i>[2011-03-22 Madrid]</i></p> - - -<p>Closed as NAD, no consensus to make a change</p> - - - -<p><b>Rationale:</b></p><p>No consensus to make a change</p> - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1330"></a>1330. Move container requirements into requirements tables</h3> -<p><b>Section:</b> 23.2 [container.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nicolai Josuttis <b>Opened:</b> 2010-03-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#container.requirements">active issues</a> in [container.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#container.requirements">issues</a> in [container.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Abstract: -</p> -<p> -In general, it seems that in a couple of places container behavior is -not described in requirement tables although it is a general behavior. -</p> - -<p> -History: -</p> - -<p> -Issue <a href="lwg-defects.html#676">676</a> added move semantics to unordered containers. -For the added insert functions the Editor requested to put their -semantic description into a requirements table rather than describing -them for each container individually. The text however was taken from -the associative containers, where we also have the semantics for each -container described. Also, <a href="lwg-defects.html#1034">1034</a> is to some extend -requesting a clarification of the requirement tables and it turned out -that in other places we have the same problem (e.g. we have no general -requirement for type pointer and const_pointer although each container -has them with issue <a href="lwg-defects.html#1306">1306</a>). -</p> - -<p> -From my personal list of functions in requirement tables -and containers, the following types/functions are missing in -requirement tables: -</p> - -<ul> -<li> -<tt>pointer</tt>, <tt>const_pointer</tt> in Table 91 (container requirements) -</li> -<li> -<p> -all copy constructors, copy constructors with allocator, - assignment operators, and insert operators - with move semantics for associative and unordered containers -</p> -<blockquote><pre> -ContType c1(c2&&) -ContType c1(c2&&,alloc) -c1 = c2&& -c.insert(val&&) -c.insert(pos,val&&) -</pre></blockquote> -</li> -</ul> - -<p> -As a special case, we lack the following requirements for all sequence -containers BUT array (so special wording or a new container category is -required): -</p> - -<ul> -<li> -<p> -constructor with only a size argument -</p> -<blockquote><pre> -ContType c(num) -</pre></blockquote> -</li> -<li> -<p> -copy constructor with allocator and move semantics -</p> -<blockquote><pre> -ContType c1(c2&&,alloc) -</pre></blockquote> -</li> -<li> -<p> -all constructors that insert multiple elements with additional allocator -</p> -<blockquote><pre> -ContType c(num, val,alloc) -ContType c(beg, end,alloc) -ContType c(initlist,alloc) -</pre></blockquote> -</li> -<li> -<p> -all resize functiuons: -</p> -<blockquote><pre> -c.resize(num) -c.resize(num,val) -</pre></blockquote> -</li> -</ul> - -<p> -Note that we also might have to add additional requirements on other -places for sequence containers because having an allocator requires -additional statements for the treatment of the allocators. E.g. swap for -containers with allocators is not specified in any requirement table. -</p> - -<p> -And finally, if we have the requirements in the requirements tables, we -can remove the corresponding descriptions for the individual container. -However, note that sequence container requirements have NO complexity -column, so that we still need container specific descriptions for the -functions listed there. -</p> - -<p><i>[ -2010 Batavia -]</i></p> - -<p> -While there is consensus that further cleaning up the container requirement -tables would be a good thing, there is no feeling that this <em>must</em> -be done in time for 0x. The issue remains open, but Deferred. -</p> - -<p><i>[ -2011 Bloomington -]</i></p> - - -<p> -Closes as NAD. There are a number of deficiencies in the way the container -requirements tables are presented, and the LWG welcomes further papers that -will help clear up this presentation. -</p> - - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1331"></a>1331. incorporate move special member functions into library</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Martin Sebor <b>Opened:</b> 2010-03-10 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Review the library portion of the spec and incorporate the newly added -core feature Move Special Member Functions (N3044). -</p> - -<p><b>Rationale:</b></p><p> -2010 Batavia: This has now been done to a large extent. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1348"></a>1348. Exception safety of unspecified types</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-64</b></p> -<p> -There are a number of unspecified types used throughout -the library, such as the container iterators. Many of these -unspecified types have restrictions or expectations on -their behaviour in terms of exceptions. Are they permitted -or required to use exception specifications, more -specifically the new <tt>noexcept</tt> specification? For example, -if <tt>vector<T>::iterator</tt> is implemented as a native pointer, -all its operations will have an (effective) <tt>noexcept</tt> -specification. If the implementation uses a class type to -implement this iterator, is it permitted or required to -support that same guarantee? -</p> - -<p><i>[ -Resolution proposed by ballot comment -]</i></p> - -<p> -Clearly state the requirements for exception -specifications on all unspecified library types. For -example, all container iterator operations should -be conditionally <tt>noexcept</tt>, with the condition -matching the same operation applied to the -allocator's <tt>pointer_type</tt>, a certain subset of which -are already required not to throw. -</p> - -<p><i>[2011-03-24 Madrid meeting]</i></p> - - -<p>Discussion:</p> -<p>Alisdair: Probably an NAD Future at least but could be NAD. -<p/> -Daniel K: Approach is not consistent with what we've decided with <tt>noexcept</tt>. -<p/> -Alisdair: Any objection to marking 1348 as NAD? -<p/> -No objections. -</p> - - - -<p><b>Rationale:</b></p><p>Standard is correct as written</p> -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1350"></a>1350. Implicit contructors accidentally made some library types move-only</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1421">1421</a></p> -<p><b>Discussion:</b></p> -<p><b>Addresses CH-15</b></p> -<p> -Due to the new rules about implicit copy and move -constructors some library facilities are now move-only. -</p> - -<p><i>[ -Resolution proposed by ballot comment -]</i></p> - -<p> -Make them copyable again. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1351"></a>1351. Replace dynamic exception specifications with <tt>noexcept</tt></h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1344">1344</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses CH-16</b></p> -<p> -Dynamic exception specifications are deprecated. -Deprecated features shouldn't be used in the Standard. -</p> - -<p><i>[ -Resolution proposed by ballot comment -]</i></p> - -<p> -Replace dynamic exception specifications with <tt>noexcept</tt>. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1352"></a>1352. Apply <tt>noexcept</tt> where library specification says "Throws: Nothing"</h3> -<p><b>Section:</b> 17 [library] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#library">active issues</a> in [library].</p> -<p><b>View all other</b> <a href="lwg-index.html#library">issues</a> in [library].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1346">1346</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses CH-17</b></p> -<p> -The introduction of <tt>noexcept</tt> makes "Throws: Nothing" clauses looking strange. -</p> - -<p><i>[ -Resolution proposed by ballot comment -]</i></p> - -<p> -Consider replacing "Throws: Nothing." clause by -the respective noexcept specification. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1358"></a>1358. Add <tt><chrono></tt> and <tt><ratio></tt> to -freestanding implementations</h3> -<p><b>Section:</b> 17.6.1.3 [compliance] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#compliance">issues</a> in [compliance].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-55</b></p> -<p> -The <tt><thread></tt> header uses <tt>duration</tt> types, found in the -<tt><chrono></tt> header, and which rely on the <tt>ratio</tt> types -declared in the <tt><ratio></tt> header. -</p> - -<p><i>[ -Extracts from lengthy Rapperswil discussion: -]</i></p> - -<p> -There is a concern that this issue is a misunderstanding of the actual -requirements of a free-standing implementation to support the <tt><thread></tt> -header. In general, a free-standanding implementation will provide an <em>empty</em> -header, specifically so that a user can test for the absence of the -<tt>_ _ STDCPP_THREADS _ _</tt> macro. This idiom as used as there is no portable -way to test for the lack of a header. -</p> -<p> -At this point, it was suggested the NB comment is trying to solve the wrong problem, -and that <tt>_ _ STDCPP_THREADS _ _</tt> should be a pre-defined macro in clause 16 -that can be tested before including <tt><thread></tt>. That would remove the -need to add additional headers to the free-standanding requirements. -</p> -<p> -It is worth noting that Japan requested <tt><ratio></tt> as a free-standing header -in their CD1 comments. No-one seemed keen to require clocks of a free-standing -implementation though. -</p> - -<p>Detlef volunteers to look at a way to redraft 17.6.1.3 p3.</p> - -<p><i>[ -Original resolution proposed by NB comment: -]</i></p> - - -<blockquote> -<p> -Add the <tt><chrono></tt> and <tt><ratio></tt> headers to the -freestanding requirements. -</p> -<p> -It might be necessary to address scaled-down -expectations of clock support in a freestanding -environment, much like <tt><thread></tt>. -</p> -</blockquote> - -<p><i>[2011-02-25: Alberto drafts wording]</i></p> - - -<p><i>[2011-03-06: Daniel observes:]</i></p> - - -<p>Accepting the proposal <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3256.html">n3256</a> -would solve this issue.</p> - -<p><i>[2011-03-24 Madrid meeting]</i></p> - - -<p>Freestanding no longer requires <tt><thread></tt> header</p> - - -<p><b>Rationale:</b></p><p>We are not adding new headers to freestanding at this point.</p> - -<p><b>Proposed resolution:</b></p> - -<ol> -<li><p>Add a new entry in Table 14 — C++ library headers:</p> - -<blockquote> -<table border="1"> -<caption>Table 14 — C++ library headers</caption> -<tr> -<td style="text-align:center;">…</td> -</tr> -<tr> -<td><tt><iterator></tt></td> -</tr> -<tr> -<td><ins><tt><library_support></tt></ins></td> -</tr> -<tr> -<td><tt><limits></tt></td> -</tr> -<tr> -<td style="text-align:center;">…</td> -</tr> -</table> -</blockquote> -</li> - -<li><p>Remove the last row 30.3 [thread.threads] <tt><threads></tt> -from Table 16 — C++ headers for freestanding implementations and insert -a new one instead (To the editor: For the actual target Clause please see the comment -in bullet 5 of this proposed resolution):</p> - -<blockquote> -<table border="1"> -<caption>Table 16 — C++ headers for freestanding implementations</caption> - -<tr> -<th>Subclause</th> -<th>Header(s)</th> -</tr> - -<tr> -<td colspan="2" style="text-align:center;">…</td> -</tr> - -<tr> -<td><del>30.3 [thread.threads] Threads</del></td> -<td><del><tt><thread></tt></del></td> -</tr> - -<tr> -<td><ins>?? Library support</ins></td> -<td><ins><tt><library_support></tt></ins></td> -</tr> - -</table> - -</blockquote> - </li> - - <li><p>Modify paragraph 17.6.1.3 [compliance] p. 3:</p> - <blockquote><p> - 3 The supplied version of the header <tt><cstdlib></tt> shall declare at least the functions - <tt>abort</tt>, <tt>atexit</tt>, <tt>at_quick_exit</tt>, <tt>exit</tt>, and <tt>quick_exit</tt> - (18.5). <del>The supplied version of the header <tt><thread></tt> shall meet the -same requirements as for a hosted implementation or including it shall have no effect</del>. The -other headers listed in this table shall meet the same requirements as for a hosted -implementation. <ins>A program can detect the presence of standard headers not listed in Table -16 using the facilities provided by the <tt><library_support></tt> header.</ins> -</p></blockquote> -</li> - -<li><p>Remove the following line from the header <tt><thread></tt> synopsis in -30.3 [thread.threads] p. 1:</p> -<blockquote><pre> -namespace std { - <del>#define __STDCPP_THREADS__ __cplusplus</del> - - class thread; - [...] -} -</pre></blockquote> -</li> - -<li><p>Add a new section in Clause 18 or 20 (or any other suitable place at -the editor's discretion):</p> - -<blockquote> -<p><ins>?? Library support [library.support]</ins></p> -<blockquote><p> -<ins>The header <tt><library_support></tt> defines an implementation-defined set -of macros to allow a program detect the presence of standard headers in freestanding -implementations. [<i>Note</i>: Hosted implementations shall provide all -standard headers, thus shall provide all macros. — <i>end note</i>]</ins> -</p></blockquote> -<blockquote><p> -<ins>For each standard header listed in Tables 14 (C++ library headers) and 15 (C++ headers for C library facilities) -that is provided by the implementation, <tt><library_support></tt> shall define a macro with name -<code>_ _HAS_<i>XXX</i>_HEADER_ _</code> where <code><i>XXX</i></code> is replaced by the uppercase version of the -name of the header. Each such macro shall expand to the value <code>_ _cplusplus</code>. -[<i>Example</i>:</ins></p> -<blockquote><pre> -<ins>#include <library_support> - -#ifdef _ _HAS_THREADS_HEADER_ _ - #include <threads> - // code that exploit the presence of threads -#else - // fallback code that doesn't rely on threads -#endif</ins> -</pre></blockquote> -<p><ins>— <i>end example</i>]</ins></p> -</blockquote> -<blockquote><p> -<ins>No other standard header shall define macros with a name beginning with <code>_ _HAS_</code> -and ending with <code>_HEADER_ _</code>.</ins> -</p></blockquote> - -</blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="1359"></a>1359. Add <tt><tuple></tt> and <tt><utility></tt> to freestanding implementations</h3> -<p><b>Section:</b> 17.6.1.3 [compliance] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#compliance">issues</a> in [compliance].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-56</b></p> -<p> -The <tt><utility></tt> header provides support for several -important C++ idioms with <tt>move</tt>, <tt>forward</tt> and <tt>swap</tt>. -Likewise, <tt>declval</tt> will be frequently used like a type trait. -In order to complete cycles introduced by <tt>std::pair</tt>, the -<tt><tuple></tt> header should also be made available. This is a -similarly primitive set of functionality, with no dependency -of a hosted environment, but does go beyond the minimal -set of functionality otherwise suggested by the -freestanding libraries. -</p> -<p> -Alternatively, split the <tt>move</tt>/<tt>forward</tt>/<tt>swap</tt>/<tt>declval</tt> -functions out of <tt><utility></tt> and into a new primitive header, -requiring only that of freestanding implementation. -</p> - -<p><i>[ -Summary of Rapperswil discusions -]</i></p> - -<p> -The preference of the meeting was to extract the rvalue-reference related utilities -and swap into a freestanding header, but there was no clear preference for a name. -Howard suggested simply dropping them into <tt><type_traits></tt> as both -these utilities and type traits are used pretty much everywhere in the library -implementation, it is the most convenient place to keep them (from an implementer's -perspective). -</p> - -<p> -Poll: Two-way: New header for forward, move, swap, move_with_noexcept and declval vs. -calling out forward, move, swap, move_with_noexcept and declval as freestanding explicitly? - -SF new header: 4 WF new header: 3 WF call out as freestanding: 1 SF call out as freestanding: 2 - -Alisdair: Willing to write up both solutions, give us some time to think on it. - -Action: Need an issue and proposed wording for GB 56 - Alisdair to draft both options as in the last poll. -</p> - -<p><i>[ -Resolution proposed by ballot comment -]</i></p> - -<blockquote> -<p> -Add <tt><utility></tt> and <tt><tuple></tt> to table 15, headers -required for a free-standing implementation. -</p> -</blockquote> - -<p><i>[ -2010-Batavia: -]</i></p> - -<p> -Closed as NAD, reversing the decision at Rapperswil. -</p> -<p> -The consensus was that -any freestanding implementation is going to feel compelled to offer the important -features of <tt><utility></tt> even if we do not make them a freestanding -requirement; breaking out additional small headers may have additional costs at -compile time, and while the critical <tt>move</tt>-related functions could migrate -to <tt><type_traits></tt>, the header name is far from appealing; adding the -whole of <tt><utility></tt> starts to drag in dependencies on <tt><tuple></tt> -and <tt><memory></tt>, so we prefer to place the burden of slicing or supporting -this whole header on free-standing vendors. -</p> - - - -<p><b>Proposed resolution:</b></p> - - -<p><b>Rationale:</b></p><p>No consensus for a change at this time.</p> - - - - -<hr> -<h3><a name="1361"></a>1361. Does use of <tt>std::size_t</tt> in a header imply that typedef name is available to users?</h3> -<p><b>Section:</b> 17.6.2 [using] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-58</b></p> -<p> -It is not clear whether a library header specified in terms -of a typedef name makes that same typedef name -available for use, or if it simply requires that the specified -type is an alias of the same type, and so the typedef name -cannot be used without including the specific header that -defines it. For example, is the following code required to -be accepted: -</p> -<blockquote><pre> -#include <vector> -std::size_t x = 0; -</pre></blockquote> -<p> -Most often, this question concerns the typedefs defined in -header <tt><cstddef></tt> -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<p> -Add a paragraph under 17.6.2 [using] clarifying whether -or not headers specified in terms of <tt>std::size_t</tt> can -be used to access the typedef <tt>size_t</tt>, or whether -the header <tt><cstddef></tt> must be included to reliably -use this name. -</p> -<p><i>[Batavia: NAD - see rationale below]</i></p> - - - - -<p><b>Proposed resolution:</b></p> - -<p><b>Rationale:</b></p><p>The standard is correct as written.</p> - - - - -<hr> -<h3><a name="1369"></a>1369. <tt>rethrow_exception</tt> may introduce data races</h3> -<p><b>Section:</b> 18.8.5 [propagation] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#propagation">issues</a> in [propagation].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-74</b></p> -<p> -One idea for the <tt>exception_ptr</tt> type was that a reference-counted -implementation could simply 'reactivate' the same -exception object in the context of a call to -<tt>rethrow_exception</tt>. Such an implementation would allow -the same exception object to be active in multiple threads -(such as when multiple threads join on a <tt>shared_future</tt>) -and introduce potential data races in any exception -handler that catches exceptions by reference - notably -existing library code written before this capability was -added. <tt>rethrow_exception</tt> should <em>always</em> make a copy -of the target exception object. -</p> - -<p><i>[Resolution suggested by NB comment]</i></p> - - -<p> -Add the following to 18.8.5, [propogation] -</p> -<blockquote><p><ins> -<i>Throws</i>: a copy of the exception object to which <tt>p</tt> refers. -</ins></p></blockquote> - -<p><i>[2011-03-15: Anthony drafts wording]</i></p> - - -<p><i>[2011-03-23 Madrid meeting]</i></p> - - -<p>No consensus for a change</p> - - - -<p><b>Rationale:</b></p><p>It would break too many existing implementations</p> - -<p><b>Proposed resolution:</b></p> - -<ol> -<li><p>Alter 15.1 [except.throw] p. 5 as follows:</p> - -<blockquote><p> -5 When the thrown object is a class object, the copy/move constructor and the destructor shall be accessible, -even if the copy/move operation is elided (12.8 [class.copy]). <ins>The copy constructor shall be -accessible, and is odr-used (3.2 [basic.def.odr]), even if the copy operation is elided, -or a move constructor used to construct the exception object.</ins> -</p></blockquote> -</li> - -<li><p>Alter 18.8.5 [propagation] p. 7 as follows:</p> - -<blockquote><pre> -exception_ptr current_exception() noexcept; -</pre><blockquote> -<p> -7 <i>Returns</i>: An <tt>exception_ptr</tt> object that refers to <del>the currently handled exception -(15.3 [except.handle]) or</del> a copy of the currently handled exception, or a null <tt>exception_ptr</tt> -object if no exception is being handled. The referenced object shall remain valid at least as long as there -is an <tt>exception_ptr</tt> object that refers to it. If the function needs to allocate memory and the -attempt fails, it returns an <tt>exception_ptr</tt> object that refers to an instance of <tt>bad_alloc</tt>. -It is unspecified whether the return values of two successive calls to <tt>current_exception</tt> refer to -the same exception object. [ <i>Note</i>: That is, it is unspecified whether <tt>current_exception</tt> -creates a new copy each time it is called. — <i>end note</i> ] If the attempt to copy the current -exception object throws an exception,<ins> or is otherwise not possible,</ins> the function returns an -<tt>exception_ptr</tt> object that refers to the thrown exception <ins>if any</ins> or, <del>if this is not possible,</del> -to an instance of <tt>bad_exception</tt>. [ <i>Note</i>: The copy constructor of the thrown exception -may also fail, so the implementation is allowed to substitute a <tt>bad_exception</tt> object to avoid -infinite recursion. — <i>end note</i> ] -</p> -</blockquote></blockquote> -</li> - -<li><p>Alter 18.8.5 [propagation] p. 9 and add a new paragraph after p. 9 as follows:</p> - -<blockquote><pre> -[[noreturn]] void rethrow_exception(exception_ptr p); -</pre><blockquote> -<p> -8 <i>Requires</i>: <tt>p</tt> shall not be a null pointer. -<p/> -9 <i>Throws</i>: <ins>a copy of</ins> the exception object to which <tt>p</tt> refers<ins>, or any exception -thrown by the attempt to copy the exception object to which <tt>p</tt> refers</ins>. -<p/> -<ins>? <i>Synchronization</i>: Calls to <tt>rethrow_exception</tt> on <tt>exception_ptr</tt> objects -that refer to the same exception object shall appear to occur in a single total order. The completion -of each call shall synchronize with (1.10 [intro.multithread]) the next call in that total order.</ins> -</p> -</blockquote></blockquote> -</li> -</ol> - - - - - - -<hr> -<h3><a name="1371"></a>1371. Standard exceptions require stronger no-throw guarantees</h3> -<p><b>Section:</b> 19 [diagnostics] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-75</b></p> -<p> -None of the exception types defined in clause 19 are -allowed to throw an exception on copy or move -operations, but there is no clear specification that the -operations have an exception specification to prove it. -Note that the implicitly declared constructors, taking the -exception specification from their base class (ultimately -<tt>std::exception</tt>) will implicitly generate a <tt>noexcept</tt> -exception specification if all of their data members -similarly declare <tt>noexcept</tt> operations. As the -representation is unspecified, we cannot assume nonthrowing -operations unless we explicitly state this as a -constraint on the implementation. -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<p> -Add a global guarantee that all exception types -defined in clause 19 that rely on implicitly declared -operations have a non-throwing exception -specification on those operations. -</p> - -<p><i>[ -2010 Batavia: -]</i></p> - -<p> -This is addressed by the current words in 18.8.1 [exception], p2 -</p> -<blockquote><p> -Each standard library class <tt>T</tt> that derives from class <tt>exception</tt> -shall have a publicly accessible copy constructor and a publicly accessible copy -assignment operator that do not exit with an exception. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1373"></a>1373. Customizable traits should have their own headers</h3> -<p><b>Section:</b> 20.2 [utility] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#utility">active issues</a> in [utility].</p> -<p><b>View all other</b> <a href="lwg-index.html#utility">issues</a> in [utility].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-79</b></p> -<p> -The library provides several traits mechanisms intended a -customization points for users. Typically, they are -declared in headers that are growing quite large. This is -not a problem for standard library vendors, who can -manage their internal file structure to avoid large -dependencies, but can be a problem for end users who -have no option but to include these large headers. -</p> - -<p><i>[ -2010 Rapperswil -]</i></p> - -<p> -There was no enthusiasm for touching <tt>char_traits</tt> or <tt>regex_traits</tt>. -Consensus to move <tt>iterator_traits</tt>, <tt>allocator_traits</tt> -and <tt>pointer_traits</tt> to their own respective headers once wording supplied. -</p> - -<p><i>[ -2010 Rapperswil -]</i></p> - -<p> -After some discussion, consensus is that moving these features into separate -headers does not buy much in practice, as the larger headers will inevitably -be included anyway. Resolve as NAD. -</p> - -<p><i>[ -Resolution proposed in ballot comment -]</i></p> - -<p> -Move the following traits classes into their own -headers, and require the existing header to -<tt>#include</tt> the traits header to support backwards -compatibility: -</p> -<blockquote><pre> -iterator_traits (plus the iterator tag-types) -allocator_traits -pointer_traits -char_traits -regex_traits -</pre></blockquote> - -<p><i>[ -2010 Batavia: -]</i></p> - -<p> -Closed as NAD with the rationale below. -</p> - - - -<p><b>Rationale:</b></p><p> -This suggest is not a defect, as the likely benefit is small, if any, -compared to the cost of not just implementating the feature, but also -explaining/teaching it. -</p> - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1374"></a>1374. Clarify moved-from objects are "toxic"</h3> -<p><b>Section:</b> 17.6.3.1 [utility.arg.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#utility.arg.requirements">issues</a> in [utility.arg.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-85</b></p> -<p> -20.2.1 Table 34 "MoveConstructible requirements" says -"Note: rv remains a valid object. Its state is unspecified". -Some components give stronger guarantees. For -example, moved-from <tt>shared_ptr</tt>s are guaranteed <tt>empty</tt> -(20.9.11.2.1/25). -In general, what the standard really should say (preferably -as a global blanket statement) is that moved-from objects -can be destroyed and can be the destination of an -assignment. Anything else is radioactive. For example, -containers can be "emptier than empty". This needs to be -explicit and required generally. -</p> -<p> -Note: The last time that one of us mentioned "emptier -than empty" (i.e. containers missing sentinel nodes, etc.) -the objection was that containers can store sentinel nodes -inside themselves in order to avoid dynamically allocating -them. This is unacceptable because -</p> -<p> -(a) it forces existing implementations (i.e. Dinkumware's, Microsoft's, -IBM's, etc.) to change for no good reason (i.e. permitting more -operations on moved-from objects), and -</p> -<p> -(b) it invalidates end-iterators when swapping containers. (The Working -Paper currently permits end-iterator invalidation, which we -consider to be wrong, but that's a separate argument. In -any event, <em>mandating</em> end-iterator invalidation is very -different from permitting it.) -</p> - -<p><i>[ -Resolution proposed in ballot comment -]</i></p> - -<p> -State as a general requirement that moved-from -objects can be destroyed and can be the -destination of an assignment. Any other use is -undefined behavior. -</p> - - -<p><b>Proposed resolution:</b></p> -<p>Resolved by <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3241.html">N3241</a></p> - - - - - -<hr> -<h3><a name="1375"></a>1375. <tt>reference_type</tt> should not have been removed from the -allocator requirements</h3> -<p><b>Section:</b> 17.6.3.5 [allocator.requirements] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#allocator.requirements">active issues</a> in [allocator.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#allocator.requirements">issues</a> in [allocator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-closed.html#1318">1318</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US-87</b></p> -<p> -<tt>reference_type</tt> should not have been removed from the -allocator requirements. Even if it is always the same as -<tt>value_type&</tt>, it is an important customization point for -extensions and future features. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -In [allocator.requirements] Table 42 - Allocotor Requirements, -Add a row (after <tt>value_type</tt>) with columns: -</p> -<blockquote><p> -Expression: <ins><tt>X::reference_type</tt></ins><BR/> -Return type: <ins><tt>T&</tt></ins><BR/> -Assertion/note...: (empty)<BR/> -Default: <ins><tt>T&</tt></ins><BR/> -</p></blockquote> -<p> -[allocator.traits]: -</p> -<blockquote><pre> -namespace std { - template <class Alloc> struct allocator_traits { - typedef Alloc allocator_type; - - typedef typename Alloc::value_type value_type; - - typedef <i>see below</i> pointer; - typedef <i>see below</i> const_pointer; - typedef <i>see below</i> void_pointer; - typedef <i>see below</i> const_void_pointer; - <ins>typedef value_type& reference_type;</ins> -</pre></blockquote> -<p> -Add <tt>reference_type</tt> to -allocator_traits template, defaulted to -value_type&. -</p> - - - - - -<hr> -<h3><a name="1376"></a>1376. Allocator interface is not backward compatible</h3> -<p><b>Section:</b> 17.6.3.5 [allocator.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#allocator.requirements">active issues</a> in [allocator.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#allocator.requirements">issues</a> in [allocator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-88</b></p> -<p> -Allocator interface is not backward compatible. -</p> - -<p><i>[ -Resolution proposed by ballot comment -]</i></p> - -<p> -See Appendix 1 - Additional Details -</p> - -<p><i>[ -2010-10-24 Daniel adds: -]</i></p> - - -<blockquote><p> -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3165.pdf">n3165</a> provides an alternative resolution. -</p></blockquote> - -<p><i>[ -2910 Batavia: -]</i></p> - -<p> -Closed as NAD - withdrawn by the submitter. -</p> - - -<p><b>Proposed resolution:</b></p><p> -See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3165.pdf">n3165</a> -</p> - -<p><b>Rationale:</b></p><p>Withdrawn by the submitter.</p> - - - - -<hr> -<h3><a name="1395"></a>1395. Inconsistent reference links should be unified</h3> -<p><b>Section:</b> 20.10.6 [meta.rel] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Japan <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#meta.rel">issues</a> in [meta.rel].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses JP-32</b></p> -<p> -Representations of reference link are not unified. -Most reference links to clause (table) number, say X, are -in the form "Clause X" ("Table X") capitalized, and -subsection Y.Y.Y is referenced with its number only in the -form "Y.Y.Y". Whether they are parenthesized or not -depends on the context. -However there are some notations "(Z)" consisting of only -a number Z in parentheses to confer Clause or Table -number Z. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change "(10)" to "(Clause 10)". -</p> - - - - - -<hr> -<h3><a name="1398"></a>1398. Users should be able to specialize functors without depending on whole <tt><functional></tt> header</h3> -<p><b>Section:</b> 20.9 [function.objects] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#function.objects">issues</a> in [function.objects].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-96</b></p> -<p> -The function templates <tt>hash</tt>, <tt>less</tt> and <tt>equal_to</tt> -are important customization points for user-defined types to -be supported by several standard containers. These are -accessed through the <tt><functional></tt> header which has -grown significantly larger in C++0x, exposing many more -facilities than a user is likely to need through there own -header, simply to declare the necessary specialization. -There should be a smaller header available for users to -make the necessary customization. -</p> - -<p><i>[ -Resolution proposed by ballot comment -]</i></p> - -<p> -Provide a tiny forwarding header for important -functor types in the <tt><functional></tt> header that a -user may want to specialize. This should contain -the template declaration for <tt>equal_to</tt>, <tt>hash</tt> and -<tt>less</tt>. -</p> - -<p><i>[ -Rapperswill summary -]</i></p> - -<p>Alisdair: Would recommend NAD unless someone takes the issue. </p> - -<p>Daniel: Volunteers to write a paper for this. </p> - -<p><i>[ -2010-11-07 Daniel provides a paper available on the Batavia document list -]</i></p> - - -<p><i>[ -2010 Batavia: -]</i></p> - -<p> -Closed as NAD - the consensus was that forwarding headers such as -<tt><iosfwd></tt> do not bring the expected benefits, and are -not widely used (to the surprise of some active users in the room!). -Without real experience reporting a benefit, there is no further interest -in pursuing this issue as an extension - hence NAD rather than NAD Future. -</p> - - - -<p><b>Rationale:</b></p><p>No consensus to make a change</p> - -<p><b>Proposed resolution:</b></p> -<p> -See paper "Forwarding <tt><functional></tt> functor templates" -on the Batavia LWG document list -</p> - - - - - -<hr> -<h3><a name="1411"></a>1411. Add a compile-time flag to detect <tt>monotonic_clock</tt></h3> -<p><b>Section:</b> X [time.clock.monotonic] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> DIN <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#time.clock.monotonic">issues</a> in [time.clock.monotonic].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1410">1410</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses DE-20</b></p> -<p> -The library component <tt>monotonic_clock</tt> is conditionally -supported, but no compile-time flag exists that allows -user-code to query its existence. Further-on there exist no -portable means to simulate such a query. (To do so, user -code would be required to add types to namespace -<tt>std::chrono</tt>.) -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Provide a compile-time flag (preferably a macro) -that can be used to query the existence of -<tt>monotonic_clock</tt>. -</p> - - - - - -<hr> -<h3><a name="1413"></a>1413. Specify whether <tt>high_resolution_clock</tt> is a distinct type or a typedef</h3> -<p><b>Section:</b> 20.12.7.3 [time.clock.hires] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-112</b></p> -<p> -What it means for <tt>high_resolution_clock</tt> to be a synonym -is undefined. If it may or may not be a typedef, then -certain classes of programs become unportable. -</p> - -<p><i>[ -Resolution proposed in ballot comment -]</i></p> - -<p> -Require that it be a distinct class type. -</p> - -<p><i>[ -2010 Batavia -]</i></p> - -<p> -This is not a defect. Threre are a number of places in the standard where -we allow implentations to choose their preferred technique, the most obvious -example being the <tt>iterator</tt>/<tt>const_iterator</tt> types of <tt>set</tt>. -</p> -<p> -Typically, this means it is not portable to declare function overloads that differ -only in their use of these types. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1415"></a>1415. Iterator stability bans the short-string optimization</h3> -<p><b>Section:</b> 23.2.1 [container.requirements.general] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#container.requirements.general">active issues</a> in [container.requirements.general].</p> -<p><b>View all other</b> <a href="lwg-index.html#container.requirements.general">issues</a> in [container.requirements.general].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Requirements on iterators swapping allegiance would -disallow the small-string optimization. -</p> -<p><i>[ -Resolved in Rapperswil by paper N3108. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -Add an exclusion for <tt>basic_string</tt> to the sentence -beginning “Every iterator referring to an -element...”. Add a sentence to 21.4.6.8/2 saying -that iterators and references to string elements -remain valid, but it is not specified whether they -refer to the same string or the other string. -</p> - - - - - -<hr> -<h3><a name="1419"></a>1419. <tt>forward_list::erase_after</tt> should return an iterator</h3> -<p><b>Section:</b> 23.3.4 [forwardlist] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#forwardlist">issues</a> in [forwardlist].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-117</b></p> -<p> -<tt>forward_list::erase_after</tt> should return an iterator. -</p> -<p><i>[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -See Appendix 1 - Additional Details -</p> - - - - - -<hr> -<h3><a name="1433"></a>1433. <tt>random_shuffle</tt> and <tt>shuffle</tt> should have consistent signatures</h3> -<p><b>Section:</b> 25.3.12 [alg.random.shuffle] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.random.shuffle">issues</a> in [alg.random.shuffle].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1432">1432</a></p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-119</b></p> -<p> -The functions <tt>random_shuffle</tt> and <tt>shuffle</tt> both take -arguments providing a source of randomness, but one -take its argument by rvalue reference, and the other -requires an lvalue reference. The technical merits of which -form of argument passing should be settled for this -specific case, and a single preferred form used -consistently. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -[DEPENDS ON WHETHER RVALUE OR -LVALUE REFERENCE IS THE PREFERRED -FORM] -</p> - - - - - -<hr> -<h3><a name="1434"></a>1434. For <tt>min/max</tt> functions replace variadic arguments by <tt>initializer_list</tt> argument</h3> -<p><b>Section:</b> 25.4.7 [alg.min.max] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.min.max">issues</a> in [alg.min.max].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-122</b></p> -<p> -It was the LWG's intent in Pittsburgh that N2772 be applied to the WP. -</p> -<p><i>[ -Resolved in Rapperswil by paper N3106. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p>Apply N2772 to the WP.</p> - - - - - -<hr> -<h3><a name="1442"></a>1442. "happens-before" should be "synchronizes-with"</h3> -<p><b>Section:</b> 30 [thread] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Canada <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread">issues</a> in [thread].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-closed.html#1443">1443</a></p> -<p><b>Discussion:</b></p> -<p><b>Addresses CA-9, GB-122</b></p> - -<p><i>[CA-9:]</i></p> - -<p> -Imposed happens-before edges should be in -synchronizes-with<br/> -Each use of the words "happens-before" should be -replaced with the words "synchronizes-with" in the -following sentences:<br/> -27.2.3p2<br/> -30.3.1.2p6<br/> -30.3.1.5p7<br/> -30.6.4p7<br/> -30.6.9p5<br/> -30.6.10.1p23<br/> -Rationale: Happens-before is defined in 1.10p11 in a way -that (deliberately) does not make it explicitly transitively -closed. Adding edges to happens-before directly, as in -27.2.3p2 etc., does not provide transitivity with -sequenced-before or any other existing happens-before -edge. This lack of transitivity seems to be unintentional. -</p> - -<p><i>[GB-122]</i></p> - - -<p>At various points in the standard new edges are added to -happens-before, for example 27.2.3:2 adds happens-before edges between -writes and reads from a stream:</p> - -<p>If one thread makes a library call a that writes a value to a -stream and, as a result, another thread reads this value from the -stream through a library call b such that this does not result in a -data race, then a happens before b.</p> - -<p>Happens-before is defined in 1.10:11 in a deliberate way that makes it -not explicitly transitively closed. Adding edges to happens-before -directly, as in 27.2.3:2, does not provide transitivity with -sequenced-before or any other existing happens-before edge. This lack -of transitivity seems to be unintentional. In order to achieve -transitivity we suggest each edge be added to -inter-thread-happens-before as a synchronises-with edge (as per -conversation with Hans Boehm). In the standard, each use of the words -"happens-before" should be replaced with the words "synchronizes-with" -in the following sentences:</p> - -<p>27.2.3:2, -30.3.1.2:6, -30.3.1.5:7, -30.6.4:7, -30.6.9:5, -30.6.10.1:23</p> - -<p><b>Proposed resolution:</b></p> - -<p><i>[Beman provided specific wording for the proposed resolution.]</i></p> - - -<p>Change 27.2.3 Thread Safety [iostreams.threadsafety] paragraph 2:</p> - -<p>If one thread makes a library call <tt>a</tt> that writes a value to a stream -and, as a result, another thread reads this value from the stream through a library -call <tt>b</tt> such that this does not result in a data race, then <tt>a</tt> -<del>happens before</del> <ins>synchronizes with</ins> <tt>b</tt>.</p> - -<p>Change 30.3.1.2 thread constructors [thread.thread.constr] paragraph 6:</p> - -<p><i>Synchronization:</i> The invocation of the constructor <del>happens -before</del> <ins>synchronizes with</ins> the invocation of the copy of <tt>f</tt>.</p> - -<p>Change 30.3.1.5 thread members [thread.thread.member] paragraph 7:</p> - -<p><i>Synchronization:</i> The completion of the thread represented by <tt>*this</tt> -<del>happens before</del> <ins>synchronizes with</ins> (1.10) <tt>join()</tt> -<del>returns</del> <ins>returning</ins>. [ Note: Operations on <tt>*this</tt> -are not synchronized. --end note ]</p> - -<p>Change 30.6.4 Associated asynchronous state [futures.state] paragraph 7:</p> - -<p>Calls to functions that successfully set the stored result of an associated -asynchronous state synchronize with (1.10) calls to functions successfully detecting -the ready state resulting from that setting. The storage of the result (whether normal -or exceptional) into the associated asynchronous state <del>happens before</del> -<ins>synchronizes with</ins> (1.10) that state <del>is</del> <ins>being</ins> set to ready.</p> - -<p>Change 30.6.9 Function template async [futures.async] paragraph 5:</p> - -<p><i>Synchronization:</i> the invocation of <tt>async</tt> <del>happens before</del> -<ins>synchronizes with</ins> (1.10) the invocation of <tt>f</tt>. [ <i>Note</i>: this -statement applies even when the corresponding future object is moved to another thread. — <i>end -note</i> ] If the invocation is not deferred, a call to a waiting function on an asynchronous return object -that shares the associated asynchronous state created by this async call shall block until the associated -thread has completed. If the invocation is not deferred, the <tt>join()</tt> on the created thread -<del>happens before</del> <ins>synchronizes with</ins> (1.10) the first function that successfully -detects the ready status of the associated asynchronous state returns or before the function that -gives up the last reference to the associated asynchronous state returns, whichever happens first. -If the invocation is deferred, the completion of the invocation of the deferred function <del>happens -before</del> <ins>synchronizes with</ins> the calls to the waiting functions return.</p> - -<p>Change 30.6.10.1 packaged_task member functions [futures.task.members] paragraph 23:</p> - -<p><i>Synchronization:</i> a successful call to <tt>operator()</tt> synchronizes with (1.10) a call -to any member function of a <tt>future</tt>, <tt>shared_future</tt>, or <tt>atomic_future</tt> object -that shares the associated asynchronous state of <tt>*this</tt>. The completion of the invocation -of the stored task and the storage of the result (whether normal or exceptional) into the associated -asynchronous state <del>happens before</del> <ins>synchronizes with</ins> (1.10) the state <del>is</del> -<ins>being</ins> set to ready. [ Note: <tt>operator()</tt> synchronizes and serializes with other -functions through the associated asynchronous state. —end note ]</p> - - - - - - -<hr> -<h3><a name="1443"></a>1443. Imposed happens-before edges are not made transitive</h3> -<p><b>Section:</b> 30 [thread] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread">issues</a> in [thread].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-closed.html#1442">1442</a></p> -<p><b>Discussion:</b></p> - - -<p><b>Addresses GB-122</b></p> - -<p>At various points in the standard new edges are added to -happens-before, for example 27.2.3:2 adds happens-before edges between -writes and reads from a stream:</p> - -<p>If one thread makes a library call a that writes a value to a -stream and, as a result, another thread reads this value from the -stream through a library call b such that this does not result in a -data race, then a happens before b.</p> - -<p>Happens-before is defined in 1.10:11 in a deliberate way that makes it -not explicitly transitively closed. Adding edges to happens-before -directly, as in 27.2.3:2, does not provide transitivity with -sequenced-before or any other existing happens-before edge. This lack -of transitivity seems to be unintentional. In order to achieve -transitivity we suggest each edge be added to -inter-thread-happens-before as a synchronises-with edge (as per -conversation with Hans Boehm). In the standard, each use of the words -"happens-before" should be replaced with the words "synchronizes-with" -in the following sentences:</p> - -<p>27.2.3:2, -30.3.1.2:6, -30.3.1.5:7, -30.6.4:7, -30.6.9:5, -30.6.10.1:23</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Request the concurrency working group to -determine if changes are needed -</p> - - - - - -<hr> -<h3><a name="1444"></a>1444. <tt>OFF_T</tt> is not defined</h3> -<p><b>Section:</b> 27.5.4.2 [fpos.operations] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#fpos.operations">issues</a> in [fpos.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1414">1414</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses GB-123</b></p> -<p> -Several rows in table 124 specify a Return type of -'OFF_T', which does not appear to be a type defined in -this standard. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Resolve outstanding references to the removed type 'OFF_T'. -</p> - - - - - -<hr> -<h3><a name="1446"></a>1446. Move and swap for I/O streams</h3> -<p><b>Section:</b> 27.7 [iostream.format] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iostream.format">issues</a> in [iostream.format].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-138</b></p> - -<p> -For istreams and ostreams, the move-constructor does -not move-construct, the move-assignment operator does -not move-assign, and the swap function does not swap -because these operations do not manage the <tt>rdbuf()</tt> -pointer. Useful applications of these operations are -prevented both by their incorrect semantics and because -they are protected. -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<p> -In short: reverse the resolution of issue 900, then -change the semantics to move and swap the -<tt>rdbuf()</tt> pointer. Add a new protected constructor -that takes an rvalue reference to a stream and a -pointer to a streambuf, a new protected <tt>assign()</tt> -operator that takes the same arguments, and a -new protected <tt>partial_swap()</tt> function that doesn't -swap <tt>rdbuf()</tt>. -See Appendix 1 - Additional Details -</p> - -<p><i>[ -2010-10-24 Daniel adds: -]</i></p> - - -<blockquote><p> -Accepting <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3179.pdf">n3179</a> would solve this issue. -</p></blockquote> - -<p><i>[ -2010-11 Batavia -]</i></p> - -<p> -Closed as NAD. -</p> -<blockquote><p> -The Library Working Group reviewed <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3179.pdf">n3179</a> and -concluded that this change alone was not sufficient, as it would require changes to some of the derived stream types in the library. -The preference is to not make such a broad fix, and retain the current semantics. This is closed as NAD rather than NAD future as it -will be difficult to rename the new functions introduced in the C++0x revision of the standard at a later date. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1451"></a>1451. <tt>regex</tt> should support allocators</h3> -<p><b>Section:</b> 28.8 [re.regex] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#re.regex">issues</a> in [re.regex].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-active.html#1396">1396</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US-141</b></p> - -<p> -<tt>std::basic_regex</tt> should have an allocator for all the -reasons that a <tt>std::string</tt> does. For example, I can use -<tt>boost::interprocess</tt> to put a <tt>string</tt> or <tt>vector</tt> -in shared memory, but not a regex. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add allocators to regexes; see paper <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3171.pdf">N3171</a> -in the pre-Batavia mailing. -</p> - - - - - -<hr> -<h3><a name="1452"></a>1452. "target sequence" is not defined</h3> -<p><b>Section:</b> 28.10.4 [re.results.acc] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#re.results.acc">issues</a> in [re.results.acc].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-125</b></p> - -<p>The term "target sequence" is not defined (28.10.4 [re.results.acc] p. 2).</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<p> -Replace "target sequence" with "string being searched/matched" -</p> - -<p><i>[ -2010-11-01 Daniel comments: -]</i></p> - -<p> -The proposed resolution looks incomplete to me, there are more normative -usages of the term <em>target sequence</em> in clause 28, e.g. -28.12.2 [re.tokiter] p. 7. -</p> - -<p><i>[2011-03-22 Madrid meeting: Moved to NAD]</i></p> - - - - -<p><b>Rationale:</b></p><p>Standard is correct as written</p> - -<p><b>Proposed resolution:</b></p> -<p> -Wording changes are against N3126. They are intended not to conflict with the wording changes -suggested by <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3158.html">n3158</a>. -</p> -<p> -Change 28.10.4 [re.results.acc] p. 2 as indicated: -</p> -<blockquote><pre> -difference_type position(size_type sub = 0) const; -</pre><blockquote><p> -2 <em>Returns</em>: The distance from the start of the <del>target sequence</del><ins>string being matched</ins> to <tt>(*this)[sub].first</tt>. -</p></blockquote></blockquote> - - - - - -<hr> -<h3><a name="1454"></a>1454. Ensure C compatibility for atomics</h3> -<p><b>Section:</b> 29 [atomics] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics">issues</a> in [atomics].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1455">1455</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses GB-128</b></p> -<p> -WG14 has made some late changes to their specification -of atomics, and care should be taken to ensure that we -retain a common subset of language/library syntax to -declare headers that are portable to both languages. -Ideally, such headers would not require users to define -their own macros, especially not macros that map to -keywords (which remains undefined behaviour) -</p> - - -<p><i>[ -Resolution proposed by ballot comment -]</i></p> - -<p> -Depends on result of the review of WG14 work, -which is expected to be out to ballot during the -time wg21 is resolving its own ballot comments. -Liaison may also want to file comments in WG14 -to ensure compatibity from both sides. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1456"></a>1456. Missing fixed-size <tt>atomic_</tt> typedefs</h3> -<p><b>Section:</b> 29 [atomics] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics">issues</a> in [atomics].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-129</b></p> -<p> -Table 143 lists the typedefs for various atomic types -corresponding to the various standard integer typedefs, -such as <tt>atomic_int_least8_t</tt> for <tt>int_least8_t</tt>, and -<tt>atomic_uint_fast64_t</tt> for <tt>uint_fast64_t</tt>. However, there are -no atomic typedefs corresponding to the fixed-size -standard typedefs <tt>int8_t</tt>, <tt>int16_t</tt>, and so forth. -</p> -<p><i>[ -2010-10-24 Daniel adds: -]</i></p> - - -<blockquote><p> -Accepting <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3164.html">n3164</a> would solve this issue. -</p></blockquote> - -<p><i>[ -2011-02-15 Anthony corrects numbering/naming for N3225, Howard suggests improvement for the position -of '(optional)', Daniel reorders rows in harmony to remaining entries and suggests specific optionality -comments: -]</i></p> - - -<p><i>[2011-02-16 Reflector discussion]</i></p> - -<p> -Moved to Tentatively Ready after 5 votes. -</p> - -<p><i>[2011-03-16: Hans reopenes and comments]</i></p> - - -<p>WG14 briefly discussed LWG 1456. It turns out that they had previously made a conscious decision not to make a -similar change. If C++ would deviate, this would introduce a C divergence. -<p/> -We should reopen the issue and, in my opinion, probably resolve it as NAD instead. This is in a part of the standard -that is there mostly for C compatibility, so introducing divergence here seems to make no sense. -</p> - -<p><i>[2011-03-24 Madrid]</i></p> - -<p><b>Rationale:</b></p><p> -WG14 does not require these typedefs, and we see no reason to be gratuitously different. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Add the following entries to table 143: -</p> -<blockquote> -<table border="1"> -<caption>Table 146 — <tt>atomic</tt> <tt><inttypes.h></tt> typedefs</caption> -<tr> -<th>Atomic typedef</th> -<th><tt><inttypes.h></tt> type</th> -</tr> -<tr> -<td><tt>...</tt></td> -<td><tt>...</tt></td> -</tr> -<tr> -<td><tt>atomic_intmax_t</tt></td> -<td><tt>intmax_t</tt></td> -</tr> -<tr> -<td><tt>atomic_uintmax_t</tt></td> -<td><tt>uintmax_t</tt></td> -</tr> -<tr> -<td><ins><tt>atomic_int8_t </tt>// <em>iff <tt>int8_t</tt> is provided</em></ins></td> -<td><ins><tt>int8_t</tt></ins></td> -</tr> -<tr> -<td><ins><tt>atomic_uint8_t </tt>// <em>iff <tt>uint8_t</tt> is provided</em></ins></td> -<td><ins><tt>uint8_t</tt></ins></td> -</tr> -<tr> -<td><ins><tt>atomic_int16_t </tt>// <em>iff <tt>int16_t</tt> is provided</em></ins></td> -<td><ins><tt>int16_t</tt></ins></td> -</tr> -<tr> -<td><ins><tt>atomic_uint16_t </tt>// <em>iff <tt>uint16_t</tt> is provided</em></ins></td> -<td><ins><tt>uint16_t</tt></ins></td> -</tr> -<tr> -<td><ins><tt>atomic_int32_t </tt>// <em>iff <tt>int32_t</tt> is provided</em></ins></td> -<td><ins><tt>int32_t</tt></ins></td> -</tr> -<tr> -<td><ins><tt>atomic_uint32_t </tt>// <em>iff <tt>uint32_t</tt> is provided</em></ins></td> -<td><ins><tt>uint32_t</tt></ins></td> -</tr> -<tr> -<td><ins><tt>atomic_int64_t </tt>// <em>iff <tt>int64_t</tt> is provided</em></ins></td> -<td><ins><tt>int64_t</tt></ins></td> -</tr> -<tr> -<td><ins><tt>atomic_uint64_t </tt>// <em>iff <tt>uint64_t</tt> is provided</em></ins></td> -<td><ins><tt>uint64_t</tt></ins></td> -</tr> -</table> -</blockquote> - - - - - -<hr> -<h3><a name="1458"></a>1458. Overlapping evaluations are allowed</h3> -<p><b>Section:</b> 29.3 [atomics.order] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#atomics.order">active issues</a> in [atomics.order].</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.order">issues</a> in [atomics.order].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-active.html#1459">1459</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses GB-131</b></p> - -<p> -29.4 [atomics.lockfree] p.8 states: -</p> -<blockquote><p> -An atomic store shall only store a value that has been computed -from constants and program input values by a finite sequence of -program evaluations, such that each evaluation observes the values -of variables as computed by the last prior assignment in the -sequence. -</p></blockquote> -<p> -... but 1.9 [intro.execution] p.13 states: -</p> -<blockquote><p> -If A is not sequenced before B and B is not sequenced before A, -then A and B are unsequenced. [ <em>Note</em>: The execution of unsequenced -evaluations can overlap. — <em>end note</em> ] -</p></blockquote> -<p> -Overlapping executions can make it impossible to construct the sequence -described in 29.4 [atomics.lockfree] p.8. We are not sure of the intention here and do not -offer a suggestion for change, but note that 29.4 [atomics.lockfree] p.8 is the condition -that prevents out-of-thin-air reads. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Request the concurrency working group to -determine if changes are needed. Consider -changing the use of "sequence" in 29.4 [atomics.lockfree] -</p> - - - - - -<hr> -<h3><a name="1461"></a>1461. Rename all <tt>ATOMIC_*</tt> macros as <tt>STD_ATOMIC_*</tt></h3> -<p><b>Section:</b> 29 [atomics] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Canada <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics">issues</a> in [atomics].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses CA-1</b></p> -<p> -All <tt>ATOMIC_</tt>... macros should be prefixed with <tt>STD_</tt> as -in <tt>STD_ATOMIC_</tt>... to indicate they are <tt>STD</tt> macros as -other standard macros. The rationale that they all seem too long seems weak. -</p> - -<p><i>[2011-03-06: Daniel adapts suggested wording to N3242 and comments]</i></p> - - -<p>I suggest to declare this issue as NAD. Reason for this suggestion is, that -C1x is currently going to suggest exactly the same macros as additions to -header <tt><stdatomic.h></tt>, therefore C++0x should not define a -whole new set. I'm making this suggestion with the understanding that -C1x is intending to keep in sync in this regard. For example, the most -<a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf">recent -draft of C1x</a> does contain the macro <tt>ATOMIC_ADDRESS_LOCK_FREE</tt> -which has recently been removed from the C++ working draft.</p> - -<p><i>[2011-03-24]</i></p> - -<p><b>Rationale:</b></p><p> -C is not going to change the name of these macros, and it is -important they have the same name for compatibility -</p> - - - -<p><b>Proposed resolution:</b></p> -<ol> -<li><p>Change sub-clause 29.2 [atomics.syn] as indicated:</p> -<blockquote><pre> -[..] -// <em>[atomics.lockfree], lock-free property</em> -#define <ins>STD_</ins>ATOMIC_CHAR_LOCK_FREE <em>unspecified</em> -#define <ins>STD_</ins>ATOMIC_CHAR16_T_LOCK_FREE <em>unspecified</em> -#define <ins>STD_</ins>ATOMIC_CHAR32_T_LOCK_FREE <em>unspecified</em> -#define <ins>STD_</ins>ATOMIC_WCHAR_T_LOCK_FREE <em>unspecified</em> -#define <ins>STD_</ins>ATOMIC_SHORT_LOCK_FREE <em>unspecified</em> -#define <ins>STD_</ins>ATOMIC_INT_LOCK_FREE <em>unspecified</em> -#define <ins>STD_</ins>ATOMIC_LONG_LOCK_FREE <em>unspecified</em> -#define <ins>STD_</ins>ATOMIC_LLONG_LOCK_FREE <em>unspecified</em> - -// <em>[atomics.types.operations.req], operations on atomic types</em> -#define <ins>STD_</ins>ATOMIC_VAR_INIT(value) <em>see below</em> -[..] -</pre></blockquote> -</li> -<li> -<p>Change 29.4 [atomics.lockfree] p. 1 as indicated:</p> -<blockquote><pre> -#define <ins>STD_</ins>ATOMIC_CHAR_LOCK_FREE <em>implementation-defined</em> -#define <ins>STD_</ins>ATOMIC_CHAR16_T_LOCK_FREE <em>implementation-defined</em> -#define <ins>STD_</ins>ATOMIC_CHAR32_T_LOCK_FREE <em>implementation-defined</em> -#define <ins>STD_</ins>ATOMIC_WCHAR_T_LOCK_FREE <em>implementation-defined</em> -#define <ins>STD_</ins>ATOMIC_SHORT_LOCK_FREE <em>implementation-defined</em> -#define <ins>STD_</ins>ATOMIC_INT_LOCK_FREE <em>implementation-defined</em> -#define <ins>STD_</ins>ATOMIC_LONG_LOCK_FREE <em>implementation-defined</em> -#define <ins>STD_</ins>ATOMIC_LLONG_LOCK_FREE <em>implementation-defined</em> -</pre><blockquote> -<p> -1 The <tt><ins>STD_</ins>ATOMIC_..._LOCK_FREE</tt> macros indicate the lock-free property of the corresponding atomic types, [..] -</p></blockquote></blockquote> -</li> -<li> -<p>Change 29.6.5 [atomics.types.operations.req] p. 6 as indicated:</p> -<blockquote><pre> -#define <ins>STD_</ins>ATOMIC_VAR_INIT(value) <em>see below</em> -</pre><blockquote><p> -5 <em>Remarks</em>: The macro expands to a token sequence suitable for constant initialization -an atomic variable of static storage duration of a type that is initialization-compatible -with <i>value</i>. [ <i>Note</i>: This operation may need to initialize locks. — <i>end note</i> ] -Concurrent access to the variable being initialized, even via an atomic operation, constitutes -a data race. [ <em>Example:</em> -</p><blockquote><pre> -atomic<int> v = <ins>STD_</ins>ATOMIC_VAR_INIT(5); -</pre></blockquote> -<p>— <em>end example</em> ]</p> -</blockquote></blockquote> -</li> -<li> -<p>Change 29.7 [atomics.flag] p. 1+4 as indicated:</p> -<blockquote><pre> -namespace std { - [..] - #define <ins>STD_</ins>ATOMIC_FLAG_INIT <em>see below</em> -} -</pre><blockquote><p> -[..] -4 The macro <tt><ins>STD_</ins>ATOMIC_FLAG_INIT</tt> shall be defined in such a way that it can be used to initialize an object of -type <tt>atomic_flag</tt> to the clear state. For a static-duration object, that initialization shall be static. It is -unspecified whether an unitialized <tt>atomic_flag</tt> object has an initial state of set or clear. [ <em>Example:</em> -</p><blockquote><pre> -atomic_flag guard = <ins>STD_</ins>ATOMIC_FLAG_INIT; -</pre></blockquote> -<p>— <em>end example</em> ]</p> -</blockquote></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="1463"></a>1463. Inconsistent value assignment for <tt>atomic_bool</tt></h3> -<p><b>Section:</b> X [atomics.types.integral] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.types.integral">issues</a> in [atomics.types.integral].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1462">1462</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US-157</b></p> - -<p> -<tt>atomic_bool</tt> has a <tt>volatile</tt> assignment operator but not a -non-<tt>volatile</tt> operator. The other integral types have both. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Add a non-volatile assignment operator to <tt>atomic_bool</tt>. -</p> - - - - - -<hr> -<h3><a name="1470"></a>1470. "Same-ness" curiosities</h3> -<p><b>Section:</b> 29.6 [atomics.types.operations] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.types.operations">issues</a> in [atomics.types.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1474">1474</a></p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-165</b></p> - -<p> -According to 29.6 [atomics.types.operations] p. 23: -</p> -<blockquote><p> -“is the same that same as that of” is not grammatical (and is not clear) -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1471"></a>1471. Default constructor of atomics needs specification</h3> -<p><b>Section:</b> 29.6 [atomics.types.operations] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.types.operations">issues</a> in [atomics.types.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-168</b></p> - -<p> -29.6 [atomics.types.operations] around p. 4: The definition of the default constructor needs exposition. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Insert a new general prototype description following the current 29.6 [atomics.types.operations] p. 3 as indicated: -</p> -<blockquote><p> -3 [<em>Note</em>: Many operations are volatile-qualified. The “volatile as device register” semantics have not changed -in the standard. This qualification means that volatility is preserved when applying these operations to -volatile objects. It does not mean that operations on non-volatile objects become volatile. Thus, volatile -qualified operations on non-volatile objects may be merged under some conditions. -- <em>end note</em>] -</p></blockquote> -<blockquote><pre> -<ins>A::A() = default;</ins> -</pre><blockquote><p> -<ins>? <em>Effects</em>: Leaves the atomic object in an uninitialized state. -[<em>Note</em>: These semantics ensure compatiblity with <tt>C</tt>. -- <em>end note</em>]</ins> -</p></blockquote></blockquote> -<blockquote><pre> -constexpr A::A(C desired); -[..] -</pre></blockquote> - - - - - -<hr> -<h3><a name="1472"></a>1472. Incorrect semantics of <tt>atomic_init</tt></h3> -<p><b>Section:</b> 29.6 [atomics.types.operations] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.types.operations">issues</a> in [atomics.types.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-171</b></p> - -<p> -As of 29.6 [atomics.types.operations] p. 7: -<p/> -The <tt>atomic_init</tt> definition "Non-atomically assigns the -value" is not quite correct, as the <tt>atomic_init</tt> purpose is -initialization. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Change 29.6 [atomics.types.operations] p. 7 as indicated: -</p> -<blockquote><pre> -void atomic_init(volatile A *object, C desired); -void atomic_init(A *object, C desired); -</pre><blockquote><p> -7 <em>Effects</em>: <del>Non-atomically assigns the value desired to <tt>*object</tt></del><ins>Initializes <tt>*object</tt> with value -<tt>desired</tt></ins>. Concurrent access from another thread, even via an atomic operation, constitutes a data race. -<ins>[<em>Note</em>: This function should only be applied to objects that have been default constructed. These semantics ensure -compatibility with <tt>C</tt>. — <em>end note</em>]</ins> -</p></blockquote></blockquote> - - - - - -<hr> -<h3><a name="1473"></a>1473. Incomplete memory order specifications</h3> -<p><b>Section:</b> 29.6 [atomics.types.operations] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.types.operations">issues</a> in [atomics.types.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-172</b></p> - -<p> -As of 29.6 [atomics.types.operations] p. 9, 13, 17, 20: -<p/> -The order specifications are incomplete because the non-<tt>_explicit</tt> -functions do not have such parameters. -<p/> -Add a new sentence: "If the program does not specify an order, it shall be -<tt>memory_order_seq_cst</tt>." Or perhaps: "The non-_explicit -non-member functions shall affect memory as though they were _explicit with -<tt>memory_order_seq_cst</tt>." -</p> - -<p><i>[ -2010 Batavia -]</i></p> - -<p> -The Concurrency subgroup reviewed this, and deemed it NAD according to -29.6 [atomics.types.operations] paragraph 2, bullet 4. -</p> - -<p><b>Rationale:</b></p><p>The working paper is correct as written.</p> - - - -<p><b>Proposed resolution:</b></p> -<ol> -<li>Change 29.6 [atomics.types.operations] p. 9 as indicated: -<blockquote><pre> -void atomic_store(volatile A* object, C desired); -void atomic_store(A* object, C desired); -void atomic_store_explicit(volatile A *object, C desired, memory_order order); -void atomic_store_explicit(A* object, C desired, memory_order order); -void A::store(C desired, memory_order order = memory_order_seq_cst) volatile; -void A::store(C desired, memory_order order = memory_order_seq_cst); -</pre><blockquote><p> -8 <em>Requires</em>: The order argument shall not be <tt>memory_order_consume</tt>, <tt>memory_order_acquire</tt>, nor -<tt>memory_order_acq_rel</tt>. -<p/> -9 <em>Effects</em>: Atomically replaces the value pointed to by <tt>object</tt> or by this with the value of <tt>desired</tt>. -Memory is affected according to the value of <tt>order</tt>. <ins>If the program does not specify an order, it shall be -<tt>memory_order_seq_cst</tt>.</ins> -</p> -</blockquote></blockquote> -</li> -<li>Change 29.6 [atomics.types.operations] p. 13 as indicated: -<blockquote><pre> -C atomic_load(const volatile A* object); -C atomic_load(const A* object); -C atomic_load_explicit(const volatile A* object, memory_order); -C atomic_load_explicit(const A* object, memory_order); -C A::load(memory_order order = memory_order_seq_cst) const volatile; -C A::load(memory_order order = memory_order_seq_cst) const; -</pre><blockquote><p> -12 <em>Requires</em>: The order argument shall not be <tt>memory_order_release</tt> nor <tt>memory_order_acq_rel</tt>. -<p/> -13 <em>Effects</em>: Memory is affected according to the value of <tt>order</tt>. <ins>If the program does not specify an order, it shall be -<tt>memory_order_seq_cst</tt>.</ins> -<p/> -14 <em>Returns</em>: Atomically returns the value pointed to by <tt>object</tt> or by <tt>this</tt>. -</p> -</blockquote></blockquote> -</li> -<li>Change 29.6 [atomics.types.operations] p. 17 as indicated: -<blockquote><pre> -C atomic_exchange(volatile A* object, C desired); -C atomic_exchange(A* object, C desired); -C atomic_exchange_explicit(volatile A* object, C desired, memory_order); -C atomic_exchange_explicit(A* object, C desired, memory_order); -C A::exchange(C desired, memory_order order = memory_order_seq_cst) volatile; -C A::exchange(C desired, memory_order order = memory_order_seq_cst); -</pre><blockquote><p> -17 <em>Effects</em>: Atomically replaces the value pointed to by <tt>object</tt> or by <tt>this</tt> with <tt>desired</tt>. Memory -is affected according to the value of <tt>order</tt>. These operations are atomic read-modify-write operations -(1.10). <ins>If the program does not specify an order, it shall be <tt>memory_order_seq_cst</tt>.</ins> -<p/> -18 <em>Returns</em>: Atomically returns the value pointed to by <tt>object</tt> or by <tt>this</tt> immediately before the effects. -</p> -</blockquote></blockquote> -</li> -<li>Change 29.6 [atomics.types.operations] p. 20 as indicated: -<blockquote><pre> -bool atomic_compare_exchange_weak(volatile A* object, C * expected, C desired); -bool atomic_compare_exchange_weak(A* object, C * expected, C desired); -bool atomic_compare_exchange_strong(volatile A* object, C * expected, C desired); -bool atomic_compare_exchange_strong(A* object, C * expected, C desired); -bool atomic_compare_exchange_weak_explicit(volatile A* object, C * expected, C desired, - memory_order success, memory_order failure); -bool atomic_compare_exchange_weak_explicit(A* object, C * expected, C desired, - memory_order success, memory_order failure); -bool atomic_compare_exchange_strong_explicit(volatile A* object, C * expected, C desired, - memory_order success, memory_order failure); -bool atomic_compare_exchange_strong_explicit(A* object, C * expected, C desired, - memory_order success, memory_order failure); -bool A::compare_exchange_weak(C & expected, C desired, - memory_order success, memory_order failure) volatile; -bool A::compare_exchange_weak(C & expected, C desired, - memory_order success, memory_order failure); -bool A::compare_exchange_strong(C & expected, C desired, - memory_order success, memory_order failure) volatile; -bool A::compare_exchange_strong(C & expected, C desired, - memory_order success, memory_order failure); -bool A::compare_exchange_weak(C & expected, C desired, - memory_order order = memory_order_seq_cst) volatile; -bool A::compare_exchange_weak(C & expected, C desired, - memory_order order = memory_order_seq_cst); -bool A::compare_exchange_strong(C & expected, C desired, - memory_order order = memory_order_seq_cst) volatile; -bool A::compare_exchange_strong(C & expected, C desired, - memory_order order = memory_order_seq_cst); -</pre><blockquote><p> -19 <em>Requires</em>: The <tt>failure</tt> argument shall not be <tt>memory_order_release</tt> nor <tt>memory_order_acq_rel</tt>. -The <tt>failure</tt> argument shall be no stronger than the success argument. -<p/> -20 <em>Effects</em>: Atomically, compares the contents of the memory pointed to by <tt>object</tt> or by <tt>this</tt> for equality -with that in <tt>expected</tt>, and if true, replaces the contents of the memory pointed to by <tt>object</tt> or by -<tt>this</tt> with that in <tt>desired</tt>, and if false, updates the contents of the memory in expected with the -contents of the memory pointed to by <tt>object</tt> or by <tt>this</tt>. Further, if the comparison is true, memory -is affected according to the value of <tt>success</tt>, and if the comparison is false, memory is affected -according to the value of <tt>failure</tt>. When only one <tt>memory_order</tt> argument is supplied, the value of -<tt>success</tt> is <tt>order</tt>, and the value of <tt>failure</tt> is <tt>order</tt> except that a value of -<tt>memory_order_acq_rel</tt> shall be replaced by the value <tt>memory_order_acquire</tt> and a value of -<tt>memory_order_release</tt> shall be replaced by the value <tt>memory_order_relaxed</tt>. <ins>If -the program does not specify an order, it shall be <tt>memory_order_seq_cst</tt>.</ins> If the operation returns <tt>true</tt>, -these operations are atomic read-modify-write operations (1.10). Otherwise, these operations are atomic load operations. -<p/> -[..] -</p> -</blockquote></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="1475"></a>1475. weak compare-and-exchange confusion II</h3> -<p><b>Section:</b> 29.6 [atomics.types.operations] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.types.operations">issues</a> in [atomics.types.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1474">1474</a></p> -<p><b>Discussion:</b></p> -<p><b>Addresses CH-23</b></p> - -<p> -29.6 [atomics.types.operations] p. 23: The first sentence has non-English syntax. -</p> - -<p><i>[ -Resolution proposed in ballot comment: -]</i></p> - - -<p> -Change to "The weak compare-and-exchange -operations may fail spuriously, that is, return false -while leaving the contents of memory pointed to -by expected unchanged." -</p> - -<p><i>[ -Daniel translates NB comment in a proposed resolution -]</i></p> - - -<p>Change 29.6 [atomics.types.operations] p. 23 as indicated:</p> - -<blockquote><p> -23 <em>Remark</em>: <del>The weak compare-and-exchange operations may fail spuriously, that is, return false while -leaving the contents of memory pointed to by <tt>expected</tt> before the operation is the same that same -as that of the <tt>object</tt> and the same as that of <tt>expected</tt> after the operation</del><ins>The weak -compare-and-exchange operations may fail spuriously, that is, return false while leaving the contents of memory -pointed to by <tt>expected</tt> unchanged.</ins>. [ <em>Note</em>: This spurious failure enables implementation of -compare-and-exchange on a broader class of machines, e.g., loadlocked store-conditional machines. A consequence of -spurious failure is that nearly all uses of weak compare-and-exchange will be in a loop. -<p/> -When a compare-and-exchange is in a loop, the weak version will yield better performance on some -platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the -strong one is preferable. — <em>end note</em> ] -</p></blockquote> - -<p><i>[ -See <a href="lwg-defects.html#1474">1474</a> for the proposed resolution -]</i></p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1476"></a>1476. Meaningless specification of spurious failure</h3> -<p><b>Section:</b> 29.6 [atomics.types.operations] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.types.operations">issues</a> in [atomics.types.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1474">1474</a></p> -<p><b>Discussion:</b></p> - -<p><b>Addresses US-177</b></p> - -<p> -The first sentence of this paragraph doesn't make sense. -</p> - -<p><i>[ -Resolution proposed in ballot comment -]</i></p> - -<p> -Figure out what it's supposed to say, and say it. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1477"></a>1477. weak compare-and-exchange confusion III</h3> -<p><b>Section:</b> 29.6 [atomics.types.operations] <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a> - <b>Submitter:</b> BSI <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#atomics.types.operations">issues</a> in [atomics.types.operations].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p> -<p><b>Duplicate of:</b> <a href="lwg-defects.html#1474">1474</a></p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB-135</b></p> - -<p> -The first sentence of 29.6 [atomics.types.operations] p.23 was changed by n2992 but -now makes no sense: "that is, return <tt>false</tt> while leaving -the contents of memory pointed to by <tt>expected</tt> before the -operation is the same that same as that of the <tt>object</tt> and -the same as that of <tt>expected</tt> after the operation." -There's a minor editorial difference between n2992 ("is -that same as that" vs "is the same that same as that") but -neither version makes sense. -Also, the remark talks about "<tt>object</tt>" which should -probably be "<tt>object</tt> or <tt>this</tt>" to cover the member functions -which have no object parameter. -</p> - -<p><i>[ -Resolution proposed in ballot comment: -]</i></p> - -<p> -Fix the Remark to say whatever was intended. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1483"></a>1483. <tt>__STDCPP_THREADS spelling</tt></h3> -<p><b>Section:</b> 30.3 [thread.threads] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> DIN <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses DE-23</b></p> - -<p> -Predefined macros usually start and end with two -underscores, see 16.8 and FDIS 29124 = WG21 N3060 -clause 7. <tt>__STDCPP_THREADS</tt> should blend in. -</p> - -<p><i>[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -Change the macro name to <tt>__STDCPP_THREADS__</tt>. -</p> - - - - - -<hr> -<h3><a name="1485"></a>1485. Unclear <tt>thread::id</tt> specification</h3> -<p><b>Section:</b> 30.3.1.1 [thread.thread.id] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.thread.id">issues</a> in [thread.thread.id].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-184</b></p> -<p> -It is unclear when a <tt>thread::id</tt> ceases to be meaningful. -The sentence "The library may reuse the value of a -<tt>thread::id</tt> of a terminated thread that can no longer be -joined." implies that some terminated threads can be -joined. It says nothing about detached threads. -</p> -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<blockquote><p> -Require a unique <tt>thread::id</tt> for every thread that is -(1) detached and not terminated or (2) has an associated <tt>std::thread</tt> -object. -</p></blockquote> - -<p><i>[ -2010-11-22 Howard Hinnant observes -]</i></p> - - -<p> -A thread can either be running or terminated. Additionally a thread can be joined, detached, or neither. -These combine into the five possible states shown in this table: -</p> - -<table border="1"> -<tr> -<th></th><th>Running</th><th>Terminated</th> -</tr> -<tr> -<th>Neither joined nor detached</th><td>shall not reuse id</td><td>shall not reuse id</td> -</tr> -<tr> -<th>detached</th><td>shall not reuse id</td><td>may reuse id</td> -</tr> -<tr> -<th>joined</th><td>impossible state</td><td>may reuse id</td> -</tr> -</table> -<p> -Only if a thread is neither joined nor detached can it be joined. Or said differently, if a -thread has already been joined or detached, then it can not be joined. The sentence: -</p> -<blockquote><p> -The library may reuse the value of a <tt>thread::id</tt> of a terminated thread that can no longer be joined. -</p></blockquote> -<p> -precisely defines the two states shown in the above table where a thread::id may be reused. -</p> -<p> -The following program illustrates all of the possibilities: -</p> -<blockquote><pre> -#include <mutex> -#include <thread> -#include <iostream> -#include <chrono> - -std::mutex mut; - -void f() -{ - std::lock_guard<std::mutex> _(mut); - std::cout << "f id = " << std::this_thread::get_id() << " terminating\n"; -} - -void g() -{ - std::lock_guard<std::mutex> _(mut); - std::cout << "g id = " << std::this_thread::get_id() << " terminating\n"; -} - -int main() -{ - std::cout << "main id = " << std::this_thread::get_id() << "\n"; - std::thread t1(f); - std::thread(g).detach(); - std::this_thread::sleep_for(std::chrono::seconds(1)); - std::cout << "g's thread::id can be reused here because g has terminated and is detached.\n"; - std::cout << "f's thread::id can't be reused here because f has terminated but is still joinable.\n"; - std::cout << "f id = " << t1.get_id() << "\n"; - t1.join(); - std::cout << "f's thread::id can be reused here because f has terminated and is joined.\n"; - std::cout << "f id = " << t1.get_id() << "\n"; -} - -main id = 0x7fff71197ca0 -f id = 0x100381000 terminating -g id = 0x100581000 terminating -g's thread::id can be reused here because g has terminated and is detached. -f's thread::id can't be reused here because f has terminated but is still joinable. -f id = 0x100381000 -f's thread::id can be reused here because f has terminated and is joined. -f id = 0x0 -</pre></blockquote> - -<p><i>[2011-02-11 Reflector discussion]</i></p> - -<p> -Moved to Tentatively NAD after 5 votes. -</p> - - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1486"></a>1486. Value of <tt>this_thread::get_id()</tt> underspecified for detached thread</h3> -<p><b>Section:</b> 30.3.2 [thread.thread.this] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.thread.this">issues</a> in [thread.thread.this].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses CH-24</b></p> -<p> -What would be the value <tt>this_thread::get_id()</tt> when called from a detached thread? -</p> -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<p> -Add some text to clarify that <tt>get_id()</tt> still returns the same value even after detaching. -</p> - -<p><i>[ -2010-11-22 Howard Hinnant observes -]</i></p> - - -<p> -30.3.2 [thread.thread.this]/1 contains the following sentence describing <tt>this_thread::get_id()</tt>: -</p> - -<blockquote><p> -... No other thread of execution shall have this id and this thread of execution shall always have this id. -</p></blockquote> - -<p>I don't object to adding "even if detached" to this sentence, but it seems unnecessary to me. "Always" means always.</p> - -<p><i>[2011-02-11 Reflector discussion]</i></p> - -<p> -Moved to Tentatively NAD after 5 votes. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1489"></a>1489. <tt>unlock</tt> functions and unlock mutex requirements are inconsistent</h3> -<p><b>Section:</b> 30.4 [thread.mutex] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.mutex">issues</a> in [thread.mutex].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses CH-26</b></p> - -<p> -Specifications of <tt>unlock</tt> member functions and <tt>unlock</tt> -mutex requirements are inconsistent wrt to exceptions and -pre- and postconditions. -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<blockquote><p> -<tt>unlock</tt> should specifiy the precondition that the -current thread "owns the lock", this will make calls -without holding the locks "undefined behavior". -<tt>unlock</tt> in [mutex.requirements] should either be -<tt>noexcept(true)</tt> or be allowed to throw -<tt>system_error</tt> like <tt>unique_lock::unlock</tt>, or the latter -should be <tt>nothrow(true)</tt> and have the precondition -<tt>owns == true</tt>. -Furthermore <tt>unique_lock</tt>'s postcondition is wrong -in the case of a recursive mutex where <tt>owns</tt> -might stay true, when it is not the last <tt>unlock</tt> -needed to be called. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1495"></a>1495. Condition variable <tt>wait_for</tt> return value insufficient</h3> -<p><b>Section:</b> 30.5 [thread.condition] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.condition">issues</a> in [thread.condition].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-191</b></p> - -<p> -The condition variable <tt>wait_for</tt> returning <tt>cv_status</tt> is insufficient. -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<blockquote><p> -Return a duration of timeout remaining instead. -See Appendix 1 of <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3141.pdf">n3141</a> - Additional Details, p. 211 -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1496"></a>1496. <tt>condition_variable</tt> not implementable</h3> -<p><b>Section:</b> 30.5.1 [thread.condition.condvar] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.condition.condvar">issues</a> in [thread.condition.condvar].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses CH-28</b></p> - -<p> -Requiring <tt>wait_until</tt> makes it impossible to implement -<tt>condition_variable</tt> correctly using respective objects -provided by the operating system (i.e. implementing the -native_handle() function) on many platforms (e.g. POSIX, -Windows, MacOS X) or using the same object as for the -condition variable proposed for C. -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<blockquote><p> -Remove the <tt>wait_until</tt> functions or make them at least conditionally supported. -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1500"></a>1500. Consider removal of <tt>native_handle()</tt></h3> -<p><b>Section:</b> 30.5.2 [thread.condition.condvarany] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.condition.condvarany">issues</a> in [thread.condition.condvarany].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses CH-32</b></p> - -<p> -Given that the lock type can be something the underlying -doesn't know 'native_handle()' is probably -unimplementable on essentially all platforms. -</p> - -<p><i>[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -Consider the removal of 'native_handle()'. -</p> - - - - - -<hr> -<h3><a name="1503"></a>1503. "associated asynchronous state" must go</h3> -<p><b>Section:</b> 30.6.4 [futures.state] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.state">issues</a> in [futures.state].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses CH-35</b></p> -<p> -The term "associated asynchronous state" is long, ugly and misleading terminology. When -introduced we agreed upon that we should come up with a better name. Here it is: -"liaison state". Since the state is hidden and provides synchronization of a -<tt>future</tt> with its corresponding <tt>promise</tt>, we believe "liaison state" is -a much better and shorter name (liaison ~ (typically hidden) relationship) -</p> -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<blockquote><p> -Change all occurrences of "associated -asynchronous state" to "liaison state". -</p></blockquote> - - -<p><b>Proposed resolution:</b></p> -<p>The project editor may supply a more appopriate term, or use "liaison state", -at his own discretion.</p> - - - - - -<hr> -<h3><a name="1506"></a>1506. <tt>set_exception</tt> with a null pointer</h3> -<p><b>Section:</b> 30.6.5 [futures.promise] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#futures.promise">active issues</a> in [futures.promise].</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.promise">issues</a> in [futures.promise].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-198</b></p> -<p> -<tt>promise::set_exception</tt> can be called with a null pointer, -but none of the descriptions of the <tt>get()</tt> functions for the -three types of futures say what happens for this case. -</p> -<p><i>[ -Resolved in Rapperswil by a motion to directly apply the words from the ballot comment in N3102. -]</i></p> - - - - -<p><b>Proposed resolution:</b></p> -<p> -Add the following sentence to the end of -30.6.5/22: The behavior of a program that calls -<tt>set_exception</tt> with a null pointer is undefined. -</p> - - - - - -<hr> -<h3><a name="1509"></a>1509. No restriction on calling <tt>future::get</tt> more than once</h3> -<p><b>Section:</b> X [futures.atomic_future] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.atomic_future">issues</a> in [futures.atomic_future].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-202</b></p> -<p> -The note in this paragraph says "unlike <tt>future</tt>, calling <tt>get</tt> -more than once on the same <tt>atomic_future</tt> object is well -defined and produces the result again." There is nothing -in <tt>future</tt> that says anything negative about calling <tt>get</tt> -more than once. -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<p> -Remove this note, or add words to the -requirements for future that reflect what this note -says. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1510"></a>1510. Should be undefined behaviour to call <tt>atomic_future</tt> operations unless <tt>valid()</tt></h3> -<p><b>Section:</b> X [futures.atomic_future] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.atomic_future">issues</a> in [futures.atomic_future].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-203</b></p> -<p> -Both <tt>future</tt> and <tt>shared_future</tt> specify that calling most -member functions on an object for which <tt>valid() == false</tt> -produces undefined behavior. There is no such statement -for <tt>atomic_future</tt>. -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<p> -Add a new paragraph after X [futures.atomic_future]/2 with the same words as -30.6.7 [futures.shared_future]/3. -</p> - -<p><i>[ -2010-11-02 Daniel translates proposed changes into specific deltas and comments: -]</i></p> - - -<blockquote><p> -While applying the wording, I notice that 30.6.7 [futures.shared_future]/3 does -speak of the move-assignment operator, and <em>not</em> of the copy-assignment operator. -<tt>atomic_future</tt> obviously needs this to be true for the copy-assignment operator, -but I strongly assume that <tt>shared_future</tt> needs to mention both special member -assignment operators in this paragraph. To keep this consistent, the following P/R also -provides wording to fix the corresponding location for <tt>shared_future</tt>. -</p></blockquote> - - - -<p><b>Proposed resolution:</b></p> -<ol> -<li>Change 30.6.7 [futures.shared_future]/3 as indicated: -<blockquote><p> -3 The effect of calling any member function other than the destructor<ins>, the -copy-assignment operator</ins>, the move-assignment operator, or <tt>valid()</tt> -on a <tt>shared_future</tt> object for which <tt>valid() == false</tt> is undefined. -</p></blockquote> -</li> -<li>Following X [futures.atomic_future]/2, add a new paragraph: -<blockquote><p> -<ins>? The effect of calling any member function other than the destructor, the copy-assignment operator, or <tt>valid()</tt> -on a <tt>atomic_future</tt> object for which <tt>valid() == false</tt> is undefined.</ins> -</p></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="1511"></a>1511. Synchronize the move-constructor for <tt>atomic_future</tt></h3> -<p><b>Section:</b> X [futures.atomic_future] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.atomic_future">issues</a> in [futures.atomic_future].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-204</b></p> -<p> -According to the definition of <tt>atomic_future</tt>, all members -of <tt>atomic_future</tt> are synchronizing except constructors. -However, it would probably be appropriate for a move -constructor to be synchronizing on the source object. If -not, the postconditions on paragraphs 7-8, might not be -satisfied. This may be applicable if a collection of futures -are being doled out to a set of threads that process their -value. -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<p> -Make the move constructor for atomic future lock -the source -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="1512"></a>1512. Conflict in specification: block or join?</h3> -<p><b>Section:</b> 30.6.8 [futures.async] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.async">issues</a> in [futures.async].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses US-205</b></p> -<p> -30.6.8 [futures.async] p. 3: The third sentence says -"If the invocation is not deferred, a call to a waiting function -on an asynchronous return object that shares the associated asynchronous state -created by this <tt>async</tt> call shall block until the associated -thread has completed." The next sentence says "If the -invocation is not deferred, the <tt>join()</tt> on the created -thread..." Blocking until a thread completes is not -necessarily a join. -</p> - -<p><i>[ -Resolution proposed by ballot comment: -]</i></p> - -<p> -Decide whether the requirement is to block until -finished or to call join, and rewrite to match. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2006"></a>2006. <tt>emplace</tt> broken for associative containers</h3> -<p><b>Section:</b> 23.2.5 [unord.req] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pablo Halpern <b>Opened:</b> 2010-10-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#unord.req">active issues</a> in [unord.req].</p> -<p><b>View all other</b> <a href="lwg-index.html#unord.req">issues</a> in [unord.req].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The current definition of <tt>emplace(args)</tt> for associative containers as -described in Table 99 is: -</p> -<blockquote> -<p> -<i>Requires</i>: <tt>T</tt> shall be constructible from <tt>args</tt>. -<p/> -<i>Effects</i>: Inserts a <tt>T</tt> object <tt>t</tt> constructed with -<tt>std::forward<Args>(args)...</tt> if and only if there is no element -in the container with key equivalent to the key of <tt>t</tt>. The <tt>bool</tt> -component of the returned <tt>pair</tt> is <tt>true</tt> if and only if the -insertion takes place, and the iterator component of the <tt>pair</tt> -points to the element with key equivalent to the key of <tt>t</tt>. -</p> -</blockquote> -<p> -There is similar language in Table 100 for unordered associative containers. -<p/> -The first issue is editorial: <tt>T</tt> should be <tt>value_type</tt> throughout -both tables. -<p/> -The major issue is that, if the container is <tt>map</tt>, <tt>multimap</tt>, -<tt>unordered_map</tt>, or <tt>unordered_multimap</tt>, then the only way to -construct an object of <tt>value_type</tt> is to supply exactly two arguments -for <tt>Key</tt> and <tt>Value</tt>, a <tt>pair<Key,Value></tt>, or a -<tt>piecewise_construct_t</tt> followed by two <tt>tuple</tt>s. The original -<tt>emplace()</tt> proposal would have allowed you to specify a <tt>Key</tt> -value followed by any number of constructor arguments for <tt>Value</tt>. -When we removed the variadic constructor to <tt>pair</tt>, this ability went -away. I don't think that was deliberate. -<p/> -Fixing this is non-trivial, I think. I think that <tt>emplace()</tt> for <tt>map</tt> -and <tt>multimap</tt> need several overloads: one for each overloaded constructor in -<tt>pair<Key,Value></tt>, and one for the <tt>emplace(Key, valueargs...)</tt> case. -And it probably needs some SFINAE meta-programming to ensure that the last case -doesn't override any of the other ones. Alternatively, one could say that -there are exactly two cases: <tt>emplace(args)</tt> where <tt>pair<Key,Value></tt> -is constructible from <tt>args</tt>, and <tt>emplace(args)</tt> where <tt>Key</tt> is -constructible form the first <tt>arg</tt> and <tt>Value</tt> is constructible from the -rest. -<p/> -Alternatively, the status quo is to use <tt>piecewise_construct_t</tt> if you want to -construct an object. -</p> - -<p><i>[ -2010 Batavia: -]</i></p> - - -<p> -N3178 was looked at in session and moved to NAD. -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2026"></a>2026. <tt>hash</tt> should be <tt>std</tt> qualified for unordered container</h3> -<p><b>Section:</b> 23.5 [unord] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2011-02-07 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#unord">issues</a> in [unord].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Tom Plum pointed out to me that there's an apparent inconsistency in the <tt>std::</tt> qualification of template names in the unordered containers: -</p> - -<blockquote><pre> - template <class Key, - class T, - class Hash = hash<Key>, - class Pred = std::equal_to<Key>, - class Alloc = std::allocator<std::pair<const Key, T> > > - class unordered_map; -</pre></blockquote> - -<p> -Is there a reason that hash is not qualified with <tt>std::</tt>? TR1 also -does not use <tt>std::</tt> here. -</p> - -<p><i>[ -2011-02-07 Chris Jefferson adds: -]</i></p> - -<p> -I assumed (I might be wrong) it is because <tt>hash</tt> is designed to be a -customisation point, like <tt>swap</tt>. -</p> - -<p><i>[ -2011-02-07 Howard Hinnant adds: -]</i></p> - -<p>I think this is incorrect. We mean <tt>std::hash</tt>, though clients -are free to specialize <tt>std::hash</tt> on user-defined types. With the -possible exception of <tt>begin</tt>/<tt>end</tt> (which I'm not sure if -we've settled that), <tt>swap</tt> is the only intended customization point (look up a function by ADL) in the <tt>std::</tt> lib. -</p> - -<p><i>[ -2011-02-24 Chris Jefferson adds: -]</i></p> - -<p>I recommend NAD, due to 17.6.1.1 [contents] p3:</p> -<blockquote><p> -Whenever a name <tt>x</tt> defined in the standard library is mentioned, the name <tt>x</tt> is assumed to be fully qualified -as <tt>::std::x</tt>, unless explicitly described otherwise. For example, if the Effects section for library function <tt>F</tt> -is described as calling library function <tt>G</tt>, the function <tt>::std::G</tt> is meant. -</p></blockquote> - -<p><i>[2011-02-25 Reflector discussion]</i></p> - -<p> -Moved to Tentatively NAD after 5 votes. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -</p> - - - - - -<hr> -<h3><a name="2036"></a>2036. <tt>istream >> char</tt> and <tt>eofbit</tt></h3> -<p><b>Section:</b> 27.7.2.1 [istream] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2011-02-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#istream">issues</a> in [istream].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p>The question is: When a single character is extracted from an <tt>istream</tt> using <tt>operator>></tt>, -does <tt>eofbit</tt> get set if this is the last character extracted from the stream? The current standard is at -best ambiguous on the subject. 27.7.2.1 [istream]/p3 describes all extraction operations with:</p> - -<blockquote><p> -3 If <tt>rdbuf()->sbumpc()</tt> or <tt>rdbuf()->sgetc()</tt> returns <tt>traits::eof()</tt>, then the input -function, except as explicitly noted otherwise, completes its actions and does <tt>setstate(eofbit)</tt>, which may -throw <tt>ios_base::failure</tt> (27.5.5.4 [iostate.flags]), before returning. -</p></blockquote> - -<p>And 27.7.2.2.3 [istream::extractors]/p12 in describing <tt>operator>>(basic_istream<charT,traits>& in, charT& c);</tt> -offers no further clarification: -</p> - -<blockquote><p> -12 <i>Effects</i>: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of <tt>in</tt>. -After a <tt>sentry</tt> object is constructed a character is extracted from <tt>in</tt>, if one is available, and -stored in <tt>c</tt>. Otherwise, the function calls <tt>in.setstate(failbit)</tt>. -</p></blockquote> - -<p>I coded it one way in libc++, and g++ coded it another way. Chris Jefferson noted that some boost code was -sensitive to the difference and fails for libc++. Therefore I believe that it is very important that we specify -this extraction operator in enough detail that both vendors and clients know what behavior is required and expected. -</p> - -<p>Here is a brief code example demonstrating the issue:</p> - -<blockquote><pre> -#include <sstream> -#include <cassert> - -int main() -{ - std::istringstream ss("1"); - char t; - ss >> t; - assert(!ss.eof()); -}; -</pre></blockquote> - -<p>For every type capable of reading this istringstream but <tt>char</tt>, <tt>ss.eof()</tt> will be true after the -extraction (<tt>bool</tt>, <tt>int</tt>, <tt>double</tt>, etc.). So for consistency's sake we might want to have -<tt>char</tt> behave the same way as other built-in types.</p> - -<p>However Jean-Marc Bourguet offers this counter example code using an interactive stream. He argues that -setting <tt>eof</tt> inhibits reading the next line:</p> - -<blockquote><pre> -#include <iostream> - -int main() -{ - char c; - std::cin >> std::noskipws; - std::cout << "First line: "; - while (std::cin >> c) { - if (c == '\n') { - std::cout << "Next line: "; - } - } -} -</pre></blockquote> - -<p>As these two code examples demonstrate, whether or not <tt>eofbit</tt> gets set is an observable difference and it -is impacting real-world code. I feel it is critical that we clearly and unambiguously choose one behavior or the other. -I am proposing wording for both behaviors and ask the LWG to choose one (and only one!).</p> - -<p>Wording for setting <tt>eof</tt> bit:</p> - -<p>Modify 27.7.2.2.3 [istream::extractors]/p12 as follows:</p> - -<blockquote><p> -12 <i>Effects</i>: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of <tt>in</tt>. -After a <tt>sentry</tt> object is constructed a character is extracted from <tt>in</tt>, if one is available, and -stored in <tt>c</tt>. <del>Otherwise, the function calls <tt>in.setstate(failbit)</tt>.</del> <ins>If a character is -extracted and it is the last character in the pending sequence, the function calls <tt>in.setstate(eofbit)</tt>. -If a character is not extracted the function calls <tt>in.setstate(failbit | eofbit)</tt>.</ins> -</p></blockquote> - -<p>Wording for not setting <tt>eof</tt> bit:</p> - -<blockquote><p> -12 <i>Effects</i>: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of <tt>in</tt>. -After a <tt>sentry</tt> object is constructed a character is extracted from <tt>in</tt><del>, if one is available, -and stored in <tt>c</tt>. Otherwise, the function calls <tt>in.setstate(failbit)</tt>.</del> <ins>with -<tt>in.rdbuf()->sbumpc()</tt>. If <tt>traits::eof()</tt> is returned, the function calls -<tt>in.setstate(failbit | eofbit)</tt>. Otherwise the return value is converted to type <tt>charT</tt> and stored -in <tt>c</tt>.</ins> -</p></blockquote> - -<p><i>[2011-02-27: Jean-Marc Bourguet comments]</i></p> - - -<p>Just for completeness: it [the counter example] doesn't inhibit to read the next line, it inhibits the prompt -to be put at the appropriate time.</p> - -<p>More information to take into account when deciding:</p> - -<ul> -<li><p>if I'm reading correctly the section to get boolean values when <tt>boolalpha</tt> is set, there we mandate -that <tt>eof</tt> isn't set if trying to read past the end of the pending sequence wasn't needed to determine the result. -</p></li> - -<li><p> -see also the behaviour of <tt>getline</tt> (which isn't a formatted input function but won't set <tt>eof</tt> -if it occurs just after the delimiter) -</p></li> - -<li><p> -if I'm reading the C standard correctly <tt>scanf("%c")</tt> wouldn't set <tt>feof</tt> either in that situation. -</p></li> -</ul> - -<p><i>[2011-02-28: Martin Sebor comments]</i></p> - - -<p>[Responds to bullet 1 of Jean-Marc's list]</p> - -<p> -Yes, this matches the stdcxx test suite for <tt>num_get</tt> and <tt>time_get</tt> -but not <tt>money_get</tt> when the currency symbol is last. I don't see -where in the locale.money.get.virtuals section we specify whether -<tt>eofbit</tt> is or isn't set and when. -<p/> -IMO, if we try to fix the <tt>char</tt> extractor to be consistent we -should also fix all the others extractors and manipulators that -aren't consistent (including <tt>std::get_money</tt> and <tt>std::get_time</tt>). -</p> - -<p><i>[2011-03-24 Madrid meeting]</i></p> - - -<p>Dietmar convinced Howard, that the standard does already say the right words</p> - - - -<p><b>Rationale:</b></p><p>Reading the last character does not set eofbit and the standard says so already</p> - -<p><b>Proposed resolution:</b></p> -<p></p> - - - - - -<hr> -<h3><a name="2043"></a>2043. <tt>std{in,out,err}</tt> should be usable as field names</h3> -<p><b>Section:</b> 27.9.2 [c.files] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Jeffrey Yasskin <b>Opened:</b> 2011-03-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#c.files">issues</a> in [c.files].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -People often define structs and classes with fields named <tt>stdin</tt>, -<tt>stdout</tt>, or <tt>stderr</tt>. According to 27.9.2 [c.files], -though, these are macros. -<p/> -glibc defines them to themselves, allowing their non-portable use as -field names, while the Mac OS X libc defines them to either <tt>__stdoutp</tt> -or <tt>(&__sF[1])</tt>, etc depending on <tt>__DARWIN_UNIX03</tt>. It's possible to -allow their use while, as far as I can see, only requiring minor -changes to various libc's, so C++1x should allow it. -</p> - -<p><i>[ -2011 Bloomington -]</i></p> - - -<p> -Closed as NAD. This is an extension request that has been an issue for over 20 years. -Supporting the extension would place a burden on the underlying C library that we may -not be in a position to influence. -</p> - - - -<p><b>Proposed resolution:</b></p> - -<p>This wording is relative to the FDIS.</p> - -<ol> -<li><p>In 27.9.2 [c.files] add "stderr", "stdin", and "stdout" to a new Values section in Table -134 — Header <tt><cstdio></tt> synopsis:</p> - -<blockquote> -<table border="1"> -<caption>134 — Header <tt><cstdio></tt> synopsis</caption> - -<tr> -<th colspan="6" style="text-align:center;">Type Name(s)</th> -</tr> - -<tr> -<th colspan="6" style="text-align:left;">Macros:</th> -</tr> - -<tr> -<td><tt>BUFSIZ</tt></td> -<td><tt>FOPEN_MAX</tt></td> -<td><tt>SEEK_CUR</tt></td> -<td><tt>TMP_MAX</tt></td> -<td><tt>_IONBF</tt></td> -<td><tt>stdout</tt></td> -</tr> - -<tr> -<td><tt>EOF</tt></td> -<td><tt>L_tmpnam</tt></td> -<td><tt>SEEK_END</tt></td> -<td><tt>_IOFBF</tt></td> -<td><tt>stderr</tt></td> -<td> </td> -</tr> - -<tr> -<td><tt>FILENAME_MAX</tt></td> -<td><tt>NULL <cstdio></tt></td> -<td><tt>SEEK_SET</tt></td> -<td><tt>_IOLBF</tt></td> -<td><tt>stdin</tt></td> -<td> </td> -</tr> - -<tr> -<th style="text-align:left;">Types:</th> -<td><tt>FILE</tt></td> -<td><tt>fpos_t</tt></td> -<td><tt>size_t <cstdio></tt></td> -<td> </td> -<td> </td> -</tr> - -<tr> -<th colspan="6" style="text-align:left;">Functions:</th> -</tr> - -<tr> -<td colspan="6" style="text-align:center;">…</td> -</tr> - -<tr> -<th colspan="6" style="text-align:left;"><ins>Values:</ins></th> -</tr> - -<tr> -<td><ins><tt>stderr</tt></ins></td> -<td><ins><tt>stdin</tt></ins></td> -<td><ins><tt>stdout</tt></ins></td> -<td> </td> -<td> </td> -<td> </td> -</tr> - -</table> -</blockquote> - -</li> - -<li><p>Add a new paragraph after paragraph 2 as indicated:</p> - -<blockquote><p> -2 Calls to the function <tt>tmpnam</tt> with an argument of <tt>NULL</tt> may -introduce a data race (17.6.5.9) with other calls to <tt>tmpnam</tt> with an -argument of <tt>NULL</tt>.<br/> -See also: ISO C 7.9, Amendment 1 4.6.2. -<p/> -<ins>? The macros <tt>stderr</tt>, <tt>stdin</tt>, and <tt>stdout</tt> shall -expand to <tt>stderr</tt>, <tt>stdin</tt>, and <tt>stdout</tt>, respectively. -[<i>Note:</i> This allows uses of <tt>#ifdef</tt> to detect their presence, -while allowing code in other scopes to use them as identifiers. — <i>end note</i>]</ins> -</p></blockquote> -</li> - -<li><p>In C.5 [diff.library] add "stderr", "stdin", and "stdout" to -Table 150 — Standard values:</p> - -<blockquote> -<table border="1"> -<caption>Table 150 — Standard values</caption> - -<tr> -<td><tt>CHAR_BIT</tt></td> -<td><tt>FLT_DIG</tt></td> -<td><tt>INT_MIN</tt></td> -<td><tt>MB_LEN_MAX</tt></td> -</tr> - -<tr> -<td colspan="4" style="text-align:center;">…</td> -</tr> - -<tr> -<td>…</td> -<td>…</td> -<td>…</td> -<td><tt>SHRT_MIN</tt></td> -</tr> - -<tr> -<td>…</td> -<td>…</td> -<td>…</td> -<td><ins><tt>stderr</tt></ins></td> -</tr> - -<tr> -<td>…</td> -<td>…</td> -<td>…</td> -<td><ins><tt>stdin</tt></ins></td> -</tr> - -<tr> -<td>…</td> -<td>…</td> -<td>…</td> -<td><ins><tt>stdout</tt></ins></td> -</tr> - -<tr> -<td>…</td> -<td>…</td> -<td>…</td> -<td><tt>UCHAR_MAX</tt></td> -</tr> - -<tr> -<td colspan="4" style="text-align:center;">…</td> -</tr> - -</table> -</blockquote> - -</li> - -</ol> - - - - - - -<hr> -<h3><a name="2046"></a>2046. <tt>shared_future(future<R>&&)</tt> should be allowed to throw</h3> -<p><b>Section:</b> 30.6.7 [futures.shared_future] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Peter Sommerlad <b>Opened:</b> 2011-04-04 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#futures.shared_future">issues</a> in [futures.shared_future].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Requiring the constructor <tt>shared_future(future<R>&& rhs)</tt> not to throw -is a pessimisation of the case where a future is returned from a call to -<tt>async(function,launch::deferred)</tt> and possible other cases. -<p/> -Such a future not dealing with multiple threads only needs to keep (a copy of) the function -to be called it later. However, creating a <tt>shared_future</tt> from that future will require more -infrastructure, like space for the value of type <tt>R</tt>, an <tt>exception_ptr</tt>, and a synchronized -reference counter for the <tt>shared_future</tt>'s instances. -<p/> -Enforcing the constructor <tt>shared_future(future<R>&& rhs)</tt> not to throw, -implies that any implementation of <tt>future</tt> will need to pre-allocate space for <tt>shared_future</tt>'s -infrastructure, that also requires an operating system resource for synchronization, regardless -if is ever needed. -<p/> -All this came up when discussing D/N3267 and Concurrency Working Group decided that the constructor -<tt>shared_future(future<R>&& rhs)</tt> should be allowed to throw. -</p> - -<p><i>[ -2011 Bloomington -]</i></p> - - -<p> -Closed as NAD. Rationale to follow by email... -</p> - - -<p><b>Proposed resolution:</b></p> - -<p>Apply the proposed resolution of <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3269.htm">n3269</a></p> - - - - - - -<hr> -<h3><a name="2060"></a>2060. <tt>unique_ptr<T[]>(nullptr_t)</tt> missing <tt>noexcept</tt></h3> -<p><b>Section:</b> 20.8.1.3 [unique.ptr.runtime] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Howard Hinnant, Paolo Carlini <b>Opened:</b> 2011-05-27 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#unique.ptr.runtime">issues</a> in [unique.ptr.runtime].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The synopsis in 20.8.1.2 [unique.ptr.single] specifies: -</p><blockquote><pre> -constexpr unique_ptr(nullptr_t) noexcept -</pre></blockquote><p> -which looks correct to me. However the corresponding constructor in 20.8.1.3 [unique.ptr.runtime] is missing <tt>noexcept</tt>: -</p><blockquote><pre> -constexpr unique_ptr(nullptr_t) : unique_ptr() { } -</pre></blockquote> - -<p><i>[Bloomington, 2011]</i></p> - -<p> -Closed as NAD Editorial. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to the FDIS.</p> -<ol> -<li><p>Modify the synopsis in 20.8.1.3 [unique.ptr.runtime]:</p> -<blockquote><pre> -namespace std { - template <class T, class D> class unique_ptr<T[], D> { - public: - typedef see below pointer; - typedef T element_type; - typedef D deleter_type; - - // 20.7.1.3.1, constructors - constexpr unique_ptr() noexcept; - […] - constexpr unique_ptr(nullptr_t) <ins>noexcept</ins> : unique_ptr() { } - - […] - }; -} -</pre></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="2068"></a>2068. <tt>std::pair</tt> not C++03-compatible with defaulted copy c'tor</h3> -<p><b>Section:</b> 20.3.2 [pairs.pair] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2011-06-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#pairs.pair">issues</a> in [pairs.pair].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The specification of the copy semantics of the C++03 version of <tt>std::pair</tt> -is defined by the class synopsis in [lib.pairs]: -</p> -<blockquote><pre> -template <class T1, class T2> -struct pair { - typedef T1 first_type; - typedef T2 second_type; - - T1 first; - T2 second; - pair(); - pair(const T1& x, const T2& y); - template<class U, class V> pair(const pair<U, V> &p); -}; -</pre></blockquote> -<p> -The effect of this specification is, that the copy constructor is compiler-declared -with the proper form depending on the contained member types. In particular, the -instantiation of <tt>pair</tt> is well-formed with an element type that has a -copy constructor with non-const first parameter type like specialzations of <tt>auto_ptr</tt> -or any user-defined type like the following one: -</p> -<blockquote><pre> -struct A { - A(A&){} -}; -</pre></blockquote> -<p> -In contrast to container types which require <tt>CopyConstructible</tt> value types, the C++03 <tt>pair</tt> -does support these, albeit unusual, element types. -<p/> -The FDIS version of the <tt>std::pair</tt> specification does specify the same semantics by -defaulting the copy and move constructor in 20.3.2 [pairs.pair]: -</p> -<blockquote><pre> -template <class T1, class T2> -struct pair { - typedef T1 first_type; - typedef T2 second_type; - - T1 first; - T2 second; - <span style="color:#C80000">pair(const pair&) = default;</span> - <span style="color:#C80000">pair(pair&&) = default;</span> - pair(); - […] -}; -</pre></blockquote> -<p> -But according to the current core rules this makes the instantiation of e.g. <tt>std::pair<A, int></tt> -ill-formed, because of the <tt>const</tt> mismatch of the compiler-declared form of the copy constructor -with that of the defaulted declaration. -<p/> -Unfortunately there seems to be no simple library solution for this problem. If the defaulted declarations -were removed, both copy c'tor and move c'tor would be <b>deleted</b>, because there exist user-declared -copy assignment and move assignment operators in the FDIS. But these operations need to be user-defined -to realize the wanted semantics of these operations for element types that are reference types. If core -rules would not be changed to fix that, I see the following options: -</p> -<ol> -<li>Intentionally decide to break the support for element types with non-const copy c'tors in <tt>pair</tt>.</li> -<li>User-declare both copy and move ctor to at least support the instantiation of the <tt>pair</tt> specializations, -but this would still not allow to copy them by the copy constructor.</li> -<li>User-declare both the const and non-const copy ctors, the move ctor, and additionally the non-const copy assignment -operator to support the instantiation of the <tt>pair</tt> specializations and of these members. This would -support all element types as it did in C++03, but all copy/move members would be non-trivial.</li> -<li>Intentionally decide to give up support for element types that are references for <tt>pair</tt>, but -still keep the allocator support with the effect of removing all declarations of the special -copy/move members. User code that needs to use <tt>tuple</tt> instead. But this would be a rather -drastic step requiring further corrections of the draft, e.g. a change of the signature of the algorithm -<tt>minmax</tt> (not the overload with the <tt>initializer_list</tt>) with a different return type.</li> -</ol> -<p> -This problem does <b>not</b> extend as backward-compatibility problem to <tt>tuple</tt>, because the TR1 -specification did explicitly declare copy constructor and copy assignment operator via the "normal" -form: -</p> -<blockquote><pre> -tuple(const tuple&); -tuple& operator=(const tuple&); -</pre></blockquote> -<p> -</p> - -<p><i>[Bloomington, 2011]</i></p> - -<p> -Closed as NAD. -</p> - -<p> -This is an unfortunate change of behavior between C++03 and C++11, but is consistent with <tt>tuple</tt>. There is no desire to go to lengths supporting types like <tt>auto_ptr</tt> now that rvalue references are in the language. -</p> - -<p> -There may be an issue for Core/EWG to look at, so that some simple <tt>=default</tt> syntax could be used that would do the right thing. If such a facility became availabile, LWG might revisit this issue. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2073"></a>2073. Library exceptions that take string arguments</h3> -<p><b>Section:</b> 19.2 [std.exceptions], 19.5.6 [syserr.syserr], 27.5.3.1.1 [ios::failure] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Eelis van der Weegen <b>Opened:</b> 2011-08-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#std.exceptions">issues</a> in [std.exceptions].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -This is an extension issue for LWG to add constructor overloads that take a -<tt>string</tt> by an rvalue reference in order to move the string into the -exception. -</p> - - -<p><i>[2012, Kona]</i></p> - -<p> -Move to NAD. -</p> -<p> -This was discussed during C++11 standardization, and deemed (at the time) to be a conforming -extension that vendors are free to add, but there seemed no need to call it out in the standard. -Since then it has been noted that the rvalue-reference overloads do not give you the move-semantic -guarantee the proposer is thought to be looking for, as in order to meet the requirements that -copy constructors do not throw (for standard exceptions) the exceptions that store strings must -actually store a reference-counted immutable string, rather than an <tt>std::string</tt> internally. -Therefore, an rvalue-reference overload is going to have to allocate memory in exactly the same -way as copying from a <tt>const string&</tt> argument. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2079"></a>2079. Required <tt>pow()</tt> overloads</h3> -<p><b>Section:</b> 26.8 [c.math] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Steve Clamage <b>Opened:</b> 2011-08-29 <b>Last modified:</b> 2015-05-22</p> -<p><b>View other</b> <a href="lwg-index-open.html#c.math">active issues</a> in [c.math].</p> -<p><b>View all other</b> <a href="lwg-index.html#c.math">issues</a> in [c.math].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -LWG issue <a href="lwg-defects.html#550">550</a> removed the functions: -</p> -<blockquote><pre> -float pow(float, int); -double pow(double, int); -long double pow(long double, int); -</pre></blockquote> -<p> -from header <tt><cmath></tt>. This change does not seem to be mentioned in Annex C, C.2.14. -<p/> -Howard: -</p> -<blockquote><p> -N3290 26.8 [c.math]/p11 says: -</p><blockquote> -<p> -Moreover, there shall be additional overloads sufficient to ensure: -</p> -<ol> -<li>If any argument corresponding to a <tt>double</tt> parameter has type <tt>long double</tt>, -then all arguments corresponding to <tt>double</tt> parameters are effectively cast to -<tt>long double</tt>. -</li> -<li>Otherwise, if any argument corresponding to a <tt>double</tt> parameter has type <tt>double</tt> -or an integer type, then all arguments corresponding to <tt>double</tt> parameters are effectively -cast to <tt>double</tt>. -</li> -<li>Otherwise, all arguments corresponding to <tt>double</tt> parameters are effectively cast to -<tt>float</tt>. -</li> -</ol> -</blockquote> -<p> -From C99 7.12.7.4 we have: -</p> -<blockquote><pre> -double pow(double, double); -</pre></blockquote> -<p> -26.8 [c.math]/p11/b2 says that if the client calls <tt>pow(2.0f, 2)</tt>, then the -<tt>int</tt> for second argument causes the following effective call to be made: -</p> -<blockquote><pre> -pow(static_cast<double>(2.0f), static_cast<double>(2)) -> double -</pre></blockquote> -<p> -The first sentence of p11 implies that this is done by supplying the following additional overload: -</p> -<blockquote><pre> -double pow(float, int); -</pre></blockquote> -<p> -If the client calls <tt>pow(2.0, 2)</tt>, then the same reasoning (b2 again) implies the following -additional overload: -</p> -<blockquote><pre> -double pow(double, int); -</pre></blockquote> -<p> -If the client calls <tt>pow(2.0l, 2)</tt>, then b1 implies the following additional overload: -</p> -<blockquote><pre> -long double pow(long double, int); -</pre></blockquote> -<p> -In all, p11 implies hundreds (perhaps thousands?) of extra overloads. All but one of which is a superset -of the overloads required by C++98/03 (that one being <tt>pow(float, int)</tt> which had its return -type changed from <tt>float</tt> to <tt>double</tt>). -<p/> -In practice, at least some vendors implement p11 by using templated overloads as opposed to ordinary overloads. -</p></blockquote> - -<p> -Steve Clamage: -</p> -<blockquote><p> -Thanks. I didn't see that those extra overloads were actually implied by p11, despite the first sentence. -Without examples, the point is a bit subtle (at least for me). -</p></blockquote> - -<p><i>[2015-05-05 Lenexa: Move to NAD]</i></p> - -<p>Billy: I believe this is NAD.</p> -<p>STL: Oh, Steve himself agrees.</p> -<p>Wakely: The issue marked as NAD will be sufficient.</p> -<p>STL: Yes, we should get rid of this.</p> -<p>Billy: I don't see any minutes from Issaquah.</p> -<p>Marshall: Since Steve agrees, does anyone object to marking as NAD?</p> -<p>Nope.</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2082"></a>2082. Misleading complexity requirements in <tt><algorithm></tt></h3> -<p><b>Section:</b> 25 [algorithms] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nicolai Josuttis <b>Opened:</b> 2011-09-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#algorithms">active issues</a> in [algorithms].</p> -<p><b>View all other</b> <a href="lwg-index.html#algorithms">issues</a> in [algorithms].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -The <tt>partition_point()</tt> algorithm is specified with: -</p> -<blockquote><p> -<i>Complexity</i>: <i>O(log(last - first))</i> applications of <tt>pred</tt>. -</p></blockquote> -<p> -While this is correct, it gives the impression that this is a logarithmic algorithm. -But unless random access iterators are used it is not logarithmic because for advancing -the iterator we have last-first steps, which means that the complexity becomes linear here. -<p/> -Shouldn't we clarify the complexity here to something like: -</p> -<blockquote><p> -<i>Complexity</i>: logarithmic for random-access iterators and linear otherwise - (in any case <i>O(log(last - first)</i>) applications of <tt>pred</tt>). -</p></blockquote> -<p> -Or should we even require <i>O(log(last - first)</i> for random-access iterators only because -for other iterators just iterating over all elements, while calling <tt>pred</tt> for each element, -might often be faster. -</p> - -<p> -Daniel Krügler: -</p> -<blockquote><p> -I agree that especially this description is a bit misleading. I'm not -convinced that this is a real defect, because the whole bunch of -templates within <tt><algorithm></tt> document the complexity solely of -<em>applications*</em> of predicates, assignment, or swaps, but never the -complexity of traversal operations (e.g. increment or iterator -equality tests). This means, the standard is consistent for this -function template, even though it could say a bit more. -<p/> -I would like to see a wording improvement, but I would rather think that -the complexity of the predicate should be mentioned first (as in other -algorithms) and that a non-normative note could be added for -specifically this algorithm to point out that this does not imply -a logarithmic traversal complexity. The note could give more details, -by explicity pointing out the linear traversal complexity for -non-random-Access iterators. -</p></blockquote> -<p> -Howard Hinnant: -</p> -<blockquote><p> -If we are going to make such improvements, they should be made across the -board in <tt><algorithm></tt>, not to just <tt>partition_point</tt>. -For example all 4 algorithms in 25.4.3 [alg.binary.search] have the -same issue, and have since C++98. -<p/> -<tt>stable_partition</tt> and <tt>inplace_merge</tt> should be inspected as well. -<p/> -Perhaps a new paragraph in 25.1 [algorithms.general], similar to -p12 would be a better place to address this issue. -</p></blockquote> - -<p><i>[2012, Kona]</i></p> - -<p> -Move to NAD. -</p> -<p> -There was some concern that the issue, if it were to be addressed, is much larger than -the couple of algorithms called out here, and applies across the whole library. There -is no interest in looking at this or similar issues without a paper addressing the whole -library. In fairness to anyone considering writing such a paper, it should be noted -that there was not much interest in such a paper in the group, although no strong opposition -either. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2084"></a>2084. <tt>basic_string</tt> use of <tt>charT*</tt></h3> -<p><b>Section:</b> 21.4 [basic.string] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Howard Hinnant <b>Opened:</b> 2011-09-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#basic.string">active issues</a> in [basic.string].</p> -<p><b>View all other</b> <a href="lwg-index.html#basic.string">issues</a> in [basic.string].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -For C++11 we gave all of the containers, including basic_string new generalized pointer types: -</p> - -<blockquote><pre> -typedef typename allocator_traits<Allocator>::pointer pointer: -typedef typename allocator_traits<Allocator>::const_pointer const_pointer; -</pre></blockquote> - -<p> -However, the constructors, assignment, and member functions still traffic exclusively in terms -of <tt>const charT*</tt>, for example: -</p> - -<blockquote><pre> -basic_string(const charT* s, const Allocator& a = Allocator()); -</pre></blockquote> - -<p> -Was this an oversight? Did we mean instead: -</p> - -<blockquote><pre> -basic_string(const_pointer s, const Allocator& a = Allocator()); -</pre></blockquote> - -<p><b>Rationale:</b></p><p> -It's intentional. <tt>char_traits</tt> assumes that all elements of -a string can be accessed indirect on plain pointers. So <tt>basic_string</tt> -doesn't support allocators with fancy pointers or references. And we meant -to do that. -<p/> -Let's take the constructor example you called out: -</p> - -<blockquote><pre> -basic_string(const charT* s, const Allocator& a = Allocator()); -</pre></blockquote> - -<p> -This constructor allows us to create a <tt>basic_string</tt> object from a string literal. -If we were to change the pointer type, that would no longer be possible. -<p/> -There is no issue here, as the implementation of the constructor must make a -copy of the string pointed-to by the pointer 's' rather than adopt ownership of -that buffer. It is that internal copy that must make use of the <tt>allocator::pointer</tt> type. -<p/> -Now what about the return value of '<tt>c_str()</tt>', should that return an <tt>allocator::pointer</tt>? -<p/> -Again, the answer (I believe) is 'no' because this is the function that allows us -to pass the string's contents to a legacy/OS 'C' API. It is deliberately returning -a raw pointer for a reason. -<p/> -There was an issue where <tt>vector::data</tt> was changed to return an <tt>allocator::pointer</tt> -to the internal buffer, and this was changed back exactly because this was intended -to support passing to external APIs. -<p/> -Do we have a use-case where the pointer type of internal data structures of our -containers (notably <tt>basic_string</tt> and <tt>vector</tt>) need to be exposed through a public API? -All my current use-cases for <tt>allocator::pointer</tt> are specific to the implementation -of containers themselves. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2090"></a>2090. Minor Overconstraint in Mutex Types</h3> -<p><b>Section:</b> 30.4.1.2 [thread.mutex.requirements.mutex] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2011-10-17 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.mutex.requirements.mutex">issues</a> in [thread.mutex.requirements.mutex].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -30.4.1.2 [thread.mutex.requirements.mutex]/6, fourth bullet requires the -return type of <tt>m.lock()</tt> to be <tt>void</tt>. -<p/> -This is over-constrained. The true requirement is that the standard library -ignores any value that the function returns. Yes, allowing non-void return -types means that users can't store a pointer to this member function. No, -that's not the least bit important. -<p/> -[See also the discussion following c++std-lib-31318] -</p> - -<p><i>[2012, Kona]</i></p> - -<p> -This does not specify a concept; it specifies requirements on the concrete mutex types. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2107"></a>2107. Some iterator category should guarantee the lifetime of references</h3> -<p><b>Section:</b> 24.2 [iterator.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Jeffrey Yasskin <b>Opened:</b> 2011-11-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#iterator.requirements">issues</a> in [iterator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Many iterators guarantee that references and pointers returned from -their methods will outlive the iterator itself. Other useful iterators -can't guarantee this, leading to the rule in 24.2 [iterator.requirements] -p9 that "Destruction of an iterator may invalidate pointers and references -previously obtained from that iterator." -<p/> -Some algorithms can take advantage of long-lived references by -returning them, while they can adapt to short-lived references by -returning by value instead. However, there doesn't seem to be a way in -the standard to distinguish between these two types of iterators. -<p/> -The <tt>ForwardIterator</tt> requirements come close by saying "If <tt>a</tt> and <tt>b</tt> are -both dereferenceable, then <tt>a == b</tt> if and only if <tt>*a</tt> and <tt>*b</tt> are bound -to the same object." (24.2.5 [forward.iterators] p6) However, there are some -subtle ways to satisfy this rule and still return a short-lived reference, meaning -algorithms can't be guaranteed that <tt>forward_iterator_tag</tt> will imply -long-lived references. -<p/> -On the other hand, defect <a href="lwg-defects.html#198">198</a>, which added the invalidation wording -to iterator.requirements.general, refers to iterators with short-lived references -being used as arguments to reverse_iterator, which requires <tt>BidirectionalIterator</tt>s. -If <tt>ForwardIterator</tt> required long-lived references, this would be impossible. -<p/> -Either <tt>ForwardIterator</tt> should be clarified to require long-lived -references, or a new category should be added that does. -<p/> -See also the discussion around c++std-lib-31477. -<p/> -Daniel: Related to this issue is that when applying <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3066.html">N3066</a> -we unintentionally lost some forward iterator requirements from C++03, where we -had the post-conditions <tt>a == X(a)</tt> of <tt>X(a)</tt>, and <tt>u == a</tt> -of any copy operation from <tt>a</tt> to <tt>u</tt>. This wording must be restored as well. -</p> - -<p><i>[2012, Kona]</i></p> - -<p> -Move to NAD. -</p> -<p> -This issue affects only Input Iterators, as all other categories are required to return -a native reference, and are not (currently) allowed to return proxies. The issue with -Input Iterators is known, and has been present since the original standard. Any change -in this regard would be an extension requiring a more substantial paper than treatment -as a simple issue. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2113"></a>2113. Do library implementers have the freedom to add <tt>final</tt> to non-polymorphic components?</h3> -<p><b>Section:</b> 17.6.5 [conforming] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Daniel Krügler <b>Opened:</b> 2011-11-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#conforming">issues</a> in [conforming].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Related to LWG <a href="lwg-defects.html#2112">2112</a> the question has been raised whether a library implementation <em>may</em> declare -non-polymorphic library components, such as class template <tt>std::vector</tt> or <tt>std::basic_string</tt>, -as <tt>final</tt> class types. -<p/> -This issue is <em>not</em> suggesting to enforce that libraries are required to do that, it is asking -whether libraries should have the freedom to do so. -<p/> -The existing wording in 17.6.5.11 [derivation] does not give a clear permission to do so. In my opinion -this position should be clarified in either direction. -<p/> -Giving implementations this freedom would have both advantages and disadvantages. Several opponents where -worried about breakage of code of existing user implementations. On the other hand such types where not -designed to be used as base classes. Allowing implementations to mark these components as <tt>final</tt> -could allow them to provide compile-modes that are intentionally restrictive to the advantage of user code -that want to be alterted about that. Any implementation that would be concerned about user complaints would -not take advantage of this feature anyway. -<p/> -If agreement exists that such implementation freedom would be useful, wording like -</p> -<blockquote><p> -An implementation may declare additional non-virtual member function signatures within a class as <tt>final</tt>. -</p></blockquote> -<p> -or -</p> -<blockquote><p> -An implementation may declare additional class without virtual member function signatures as <tt>final</tt>. -</p></blockquote> -<p> -should be added to 17.6.5 [conforming] with corresponding exceptions of these rules (e.g. <tt>iterator</tt>, -<tt>unary_function</tt>, or <tt>pair</tt>). -<p/> -If such freedom should not exist, it seems better to clarify this as well, e.g. by adding around 17.6.5.11 [derivation]: -</p> -<blockquote><p> -An implementation shall not declare any class or any member function signature as <tt>final</tt>. -</p></blockquote> - - -<p><i>[2012, Kona]</i></p> - -<p> -Move to NAD. -</p> -<p> -Unless the library uses the keyword <tt>final</tt> in a specification, the user clearly has -freedom to derive from such a class, and so equally clearly, the library vendor does not have -freedom to add a <tt>final</tt> overrider or class attribute. Howard observed there may be -some wiggle-room with 'unspecified types' such as those returned from <tt>bind</tt> expressions, -or iterators, but we did not see a need to further clarify the issue. Note that, for example, -a <tt>vector::iterator</tt> may be implemented as a raw pointer, so users cannot generally -assume the ability to derive from unspecified library types. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2124"></a>2124. Seed sequence over-specified</h3> -<p><b>Section:</b> 26.5.1.2 [rand.req.seedseq] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alberto Ganesh Barbati <b>Opened:</b> 2012-01-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.req.seedseq">issues</a> in [rand.req.seedseq].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -The seed sequence requirements described in 26.5.1.2 [rand.req.seedseq] appear to be over-specified. -All seed sequence types are required to have a <tt>result_type</tt> nested type, a specific set of -constructors, function members <tt>size()</tt> and <tt>param()</tt>, which are never used by the library. -In fact, the only library components that actively use seed sequences are the random engines and all the -engines need is the <tt>generate()</tt> member function. In particular, library components never attempts -to construct seed sequence objects. These extraneous requirements are clearly written to describe the -library provided type <tt>seed_seq</tt> type; while it's good that seed_seq has all those constructors and -members, it's not a compelling reason to require a user-provided seed sequence type to implement all of -them. -<p/> -Suppose I want to write my own seed sequence class, this should do fine (and actually works as expected with libc++): -</p> -<blockquote><pre> -class my_seed_seq -{ - /* internals */ -public: - my_seed_seq(/* my own parameters */); - - template <class It> - void generate(It first, It last); -}; - -my_seed_seq s(/* params */); -std::default_random_engine e(s); -</pre></blockquote> -<p> -The only reason to have these extra members would be to provide some support for generic serializability/persistence -of seed sequence objects. I believe that would be out of the scope of the random library, so I doubt we will ever need -those requirements in the future. -<p/> -I therefore propose to remove all requirements from 26.5.1.2 [rand.req.seedseq] except for the presence of the -<tt>generate()</tt> function. -</p> - -<p><i>[2012, Kona]</i></p> - -<p> -Move to Tenatively NAD. (Tentative as issue was not in pre-meeting mailing) -</p> -<p> -The 'overspecification', as such, was a deliberate intent to provide guarantees consumers of the whole -random number framework may rely upon, especially in generic code. While the standard engines may be -built without relying on these guarantees, this specification is part of a commitment to a broader -framework, and Walter indicated future proposals in preparation for parallel generation of random -numbers that may depend more inimately on these existing requirements. -</p> -<p> -Alisdair noted that the <tt>result_type</tt> typedef was a call-back to how we used to specify -adaptable functors before TR1 <tt>result_of</tt> and the addition of <tt>std::bind</tt> and is -probably not something we should be actively promoting in future libraries. However, it is too -late to remove this requirement from seed sequences unless we are doing further surgery, as -recommended by this issue. -</p> -<p> -Walter notes that the <tt>result_type</tt> protocol has not been formally deprecated by the -standard. Alisdair replies that was the intent of deprecating the <tt>bind_1st</tt>/ -<tt>unary_function</tt> set of templates in C++11, although we did not say anything about -<tt>result_type</tt> in general. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to the FDIS.</p> - -<ol> -<li> -<p>Edit 26.5.1.2 [rand.req.seedseq] p2 as indicated:</p> - -<blockquote><p> -A class <tt>S</tt> satisfies the requirements of a seed sequence if the expressions shown in Table 115 are valid and -have the indicated semantics, and if <tt>S</tt> also satisfies all other requirements of this section 26.5.1.2 [rand.req.seedseq]. -In that Table and throughout this section: -</p> -<ol style="list-style-type:lower-alpha"> -<li> -<del><tt>T</tt> is the type named by <tt>S</tt>'s associated <tt>result_type</tt>;</del> -</li> -<li> -<tt>q</tt> is a value of <tt>S</tt><del> and <tt>r</tt> is a possibly const value of <tt>S</tt></del>; <ins>and</ins> -</li> -<li> -<del><tt>ib</tt> and <tt>ie</tt> are input iterators with an unsigned integer <tt>value_type</tt> of at least 32 bits;</del> -</li> -<li><tt>rb</tt> and <tt>re</tt> are mutable random access iterators with an unsigned integer <tt>value_type</tt> of at least 32 bits;</li> -<li> -<del><tt>ob</tt> is an output iterator; and</del> -</li> -<li> -<del><tt>il</tt> is a value of <tt>initializer_list<T></tt>.</del> -</li> -</ol> -</blockquote> -</li> - -<li> -<p>Ditto, in Table 115, remove all rows except the one describing <tt>q.generate(rb, re)</tt>:</p> - -<table border="1"> -<caption>Table 115 — Seed sequence requirements</caption> -<tr align="center"> -<th>Expression</th> -<th>Return type</th> -<th>Pre/Post-condition</th> -<th>Complexity</th> -</tr> - -<tr> -<td> -<del><tt>S::result_type</tt></del> -</td> -<td> -<del><tt>T</tt></del> -</td> -<td> -<del><tt>T</tt> is an unsigned integer<br/> -type (3.9.1 [basic.fundamental]) of at least 32 bits.</del> -</td> -<td> -<del>compile-time</del> -</td> -</tr> - -<tr> -<td> -<del><tt>S()</tt></del> -</td> -<td> - -</td> -<td> -<del>Creates a seed sequence with<br/> -the same initial state as all<br/> -other default-constructed seed<br/> -sequences of type <tt>S</tt>.</del> -</td> -<td> -<del>constant</del> -</td> -</tr> - -<tr> -<td> -<del><tt>S(ib,ie)</tt></del> -</td> -<td> - -</td> -<td> -<del>Creates a seed sequence having<br/> -internal state that depends on<br/> -some or all of the bits of the<br/> -supplied sequence <tt>[ib, ie)</tt>.</del> -</td> -<td> -<del><tt>𝒪(ie - ib)</tt></del> -</td> -</tr> - -<tr> -<td> -<del><tt>S(il)</tt></del> -</td> -<td> - -</td> -<td> -<del>Same as <tt>S(il.begin(),<br/> -il.end())</tt>.</del> -</td> -<td> -<del>same as<br/> -<tt>S(il.begin(),<br/> -il.end())</tt></del> -</td> -</tr> - -<tr> -<td> -<tt>q.generate(rb,re)</tt> -</td> -<td> -<tt>void</tt> -</td> -<td> -Does nothing if <tt>rb == re</tt>.<br/> -Otherwise, fills the supplied<br/> -sequence <tt>[rb, re)</tt> with 32-bit<br/> -quantities that depend on the<br/> -sequence supplied to the<br/> -constructor and possibly also<br/> -depend on the history of<br/> -<tt>generate</tt>'s previous<br/> -invocations. -</td> -<td> -<tt>𝒪(re - rb)</tt> -</td> -</tr> - -<tr> -<td> -<del><tt>r.size()</tt></del> -</td> -<td> -<del><tt>size_t</tt></del> -</td> -<td> -<del>The number of 32-bit units that<br/> -would be copied by a call to<br/> -<tt>r.param</tt>.</del> -</td> -<td> -<del>constant</del> -</td> -</tr> - -<tr> -<td> -<del><tt>r.param(ob)</tt></del> -</td> -<td> -<del><tt>void</tt></del> -</td> -<td> -<del>Copies to the given destination -a sequence of 32-bit units that<br/> -can be provided to the<br/> -constructor of a second object<br/> -of type <tt>S</tt>, and that would<br/> -reproduce in that second object<br/> -a state indistinguishable from<br/> -the state of the first object.</del> -</td> -<td> -<del><tt>𝒪(r.size())</tt></del> -</td> -</tr> - -</table> - </li> - -</ol> - - - - - - -<hr> -<h3><a name="2125"></a>2125. <tt>TimedMutex</tt> specification problem</h3> -<p><b>Section:</b> 30.4.1.3 [thread.timedmutex.requirements], 30.4.1.3.1 [thread.timedmutex.class] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">Pending NAD Editorial</a> - <b>Submitter:</b> Vicente J. Botet Escriba <b>Opened:</b> 2012-01-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.timedmutex.requirements">issues</a> in [thread.timedmutex.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Pending NAD Editorial">Pending NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -30.4.1.3.1 [thread.timedmutex.class] says: -</p> -<blockquote><p> -The class <tt>timed_mutex</tt> shall satisfy all of the <tt>TimedMutex</tt> requirements (30.4.1.3 [thread.timedmutex.requirements]). -It shall be a standardlayout class (Clause 9 [class]). -</p></blockquote> -<p> -Problem here is that 30.4.1.3 [thread.timedmutex.requirements] does not define a requirement set named "<tt>TimedMutex</tt>", -it only refers to "<i>timed mutex types</i>" -</p> - -<p><i>[See also issue <a href="lwg-closed.html#2126">2126</a>]</i></p> - - -<p><i>[2012, Portland: move to Tentatively NAD Editorial]</i></p> - -<p> -We have timed mutex type, but it is labeled timed mutex requirements -</p> -<p> -We can make a suggestion, but will send to the editor as it seems purely editorial. -There is a typo, and we don't have the timed mutex but 30.4.1.3 [thread.timedmutex.requirements] already -says timed mutex type, and we need to reuse that term down in the class to fulfil the mutex requirement. -</p> -<p><i>[To Editor:]</i></p> - -<p> -Replace this one with timed mutex type. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2126"></a>2126. Several specification problems in regard to mutex requirements</h3> -<p><b>Section:</b> 30.4.1 [thread.mutex.requirements], 30.4.1.2.1 [thread.mutex.class], 30.4.1.2 [thread.mutex.requirements.mutex], 30.4.1.2.2 [thread.mutex.recursive], 30.4.1.3 [thread.timedmutex.requirements], 30.4.1.3.1 [thread.timedmutex.class], 30.4.1.3.2 [thread.timedmutex.recursive] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">Pending NAD Editorial</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2012-01-16 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#thread.mutex.requirements">active issues</a> in [thread.mutex.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.mutex.requirements">issues</a> in [thread.mutex.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Pending NAD Editorial">Pending NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p> - 30.4.1.2.1 [thread.mutex.class]/3 says that the class mutex "shall satisfy all the <tt>Mutex</tt> requirements (30.4.1 [thread.mutex.requirements])". - 30.4.1.2.1 [thread.mutex.class] is part of 30.4.1 [thread.mutex.requirements], so at the very least, this - requirement is recursive. But worse, there is nothing that says what "the <tt>Mutex</tt> requirements" refers to. For example, - the "<tt>Lockable</tt> requirements" section starts with "A type <tt>L</tt> meets the <tt>Lockable</tt> requirements if …". There is no such - statement for "the <tt>Mutex</tt> requirements". -<p/> -Organizationally, paragraphs 1-26 in 30.4.1.2 [thread.mutex.requirements.mutex] should probably be in a subclause with a name. -(This is actually an ISO requirement, to avoid exactly this kind of ambiguous referencing) Then the first sentence of -30.4.1.2.1 [thread.mutex.class]/3 can become a note: "The class mutex meets the requirements of (whatever)", since that -subclause already says that the mutex types "shall meet the requirements set out in this section." -<p/> -And similarly for 30.4.1.2.2 [thread.mutex.recursive]/2 (<tt>recursive_mutex</tt>). -<p/> -30.4.1.3 [thread.timedmutex.requirements], Timed mutex types, also needs the same rearrangement: its introductory -requirements should be moved into a subclause, and the first sentences of 30.4.1.3.1 [thread.timedmutex.class]/2 -and 30.4.1.3.2 [thread.timedmutex.recursive]/2 should be turned into notes that refer to this new subclause and -to the new subclause in 30.4.1.2 [thread.mutex.requirements.mutex]. -</p> - -<p><i>[See also issue <a href="lwg-closed.html#2125">2125</a>]</i></p> - - -<p><i>[2012, Portland: move to Tentatively NAD Editorial]</i></p> - -<p> -Seems no real ambiguity. May need some reorg of text rather then changing the wording. -</p> -<p> -Is there much that needs to be changed? But Pete's suggestion of putting requirement in separate sub section is good. -Should be the direction to editor. -</p> -<p> -Suggest this is an editorial change. Happy with Pete's comments. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2131"></a>2131. Member function getline taking a string as parameter</h3> -<p><b>Section:</b> 27.7.2.3 [istream.unformatted] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Loïc Joly <b>Opened:</b> 2012-03-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#istream.unformatted">active issues</a> in [istream.unformatted].</p> -<p><b>View all other</b> <a href="lwg-index.html#istream.unformatted">issues</a> in [istream.unformatted].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I think the following code should be legal: -</p> -<blockquote><pre> -void f(std::istream& is) -{ - std::string s; - is.getline(s); // Would be equivalent to std::getline(is, s) -} -</pre></blockquote> - -<p><i>[2013-04-20, Bristol]</i></p> - - -<p> -Unanimous that this is a new feature request and not a issue. -<p/> -Resolution: Tentatively NAD -</p> - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3376.</p> - -<ol> -<li><p>Change the class template <tt>basic_istream</tt> synopsis, 27.7.2.1 [istream], as indicated</p> -<blockquote><pre> -namespace std { - template <class charT, class traits = char_traits<charT> > - class basic_istream : virtual public basic_ios<charT,traits> { - public: - […] - <i>// 27.7.2.3 Unformatted input:</i> - […] - basic_istream<charT,traits>& getline(char_type* s, streamsize n); - basic_istream<charT,traits>& getline(char_type* s, streamsize n, - char_type delim); - <ins>template<class Allocator> - basic_istream<charT,traits>& getline(basic_string<charT,traits,Allocator>& str); - template<class Allocator> - basic_istream<charT,traits>& getline(basic_string<charT,traits,Allocator>& str, - char_type delim);</ins> - […] - }; -} -</pre></blockquote> -</li> - -<li><p>Insert the following two new prototype descriptions after 27.7.2.3 [istream.unformatted] paragraph 24:</p> - -<blockquote> -<pre> -basic_istream<charT,traits>& getline(char_type* s, streamsize n); -</pre> -<blockquote><p> --24- <i>Returns</i>: <tt>getline(s,n,widen('\n'))</tt> -</p> -</blockquote> - -<pre> -<ins>template<class Allocator> -basic_istream<charT,traits>& getline(basic_string<charT,traits,Allocator>& str);</ins> -</pre> -<blockquote><p> -<ins>-??- <i>Returns</i>: <tt>std::getline(*this, str)</tt></ins> -</p> -</blockquote> - -<pre> -<ins>template<class Allocator> -basic_istream<charT,traits>& getline(basic_string<charT,traits,Allocator>& str, char_type delim);</ins> -</pre> -<blockquote><p> -<ins>-??- <i>Returns</i>: <tt>std::getline(*this, str, delim)</tt></ins> -</p> -</blockquote> - -</blockquote> -</li> -</ol> - - - - - - -<hr> -<h3><a name="2134"></a>2134. Redundant Mutex requirement?</h3> -<p><b>Section:</b> 30.4.1.2 [thread.mutex.requirements.mutex] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">Pending NAD Editorial</a> - <b>Submitter:</b> Pete Becker <b>Opened:</b> 2012-03-05 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#thread.mutex.requirements.mutex">issues</a> in [thread.mutex.requirements.mutex].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Pending NAD Editorial">Pending NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -30.4.1.2 [thread.mutex.requirements.mutex]/11 says that prior unlock operations <em>synchronize with</em> <tt>m.lock()</tt>. -<p/> -30.4.1.2 [thread.mutex.requirements.mutex]/19 says that if <tt>m.try_lock()</tt> succeeds, prior unlock operations -<em>synchronize with</em> the operation. -<p/> -30.4.1.2 [thread.mutex.requirements.mutex]/25 says that <tt>m.unlock()</tt> <em>synchronizes with</em> subsequent -successful lock operations. -<p/> -Does the third requirement add anything to the first two? If not, it should probably be a non-normative note. -</p> - -<p><i>[2012, Portland: move to Tentatively NAD Editorial]</i></p> - -<p> -Agree that third note should be non-normative and adds nothing. -</p> -<p> -Seems An Editorial change, but does changing a normative to non-normative wording makes it a non-editorial change? -</p> -<p> -Ask the editor. If not editorial, then we will agree on the fix as removal of the third point, -then we will put it in ready state for Bristol. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2167"></a>2167. Copy assignment requirements of Containers</h3> -<p><b>Section:</b> 23.2.1 [container.requirements.general] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Dean Michael Berris <b>Opened:</b> 2012-07-13 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#container.requirements.general">active issues</a> in [container.requirements.general].</p> -<p><b>View all other</b> <a href="lwg-index.html#container.requirements.general">issues</a> in [container.requirements.general].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Table 96 defines the general requirement for copy assignment (row 23, page 704) as: -</p> - -<table border="1"> -<caption>Table 96 — Container requirements</caption> - -<tr> -<th>Expression</th> -<th>Return type</th> -<th>Operational semantics</th> -<th>Assertion/note pre-/post-condition</th> -<th>Complexity</th> -</tr> - -<tr> -<td> -<tt>r = a</tt> -</td> -<td> -<tt>X&</tt> -</td> -<td> -<tt></tt> -</td> -<td> -post: <tt>r == a.</tt> -</td> -<td> -linear -</td> -</tr> - -</table> - -<p> -However there is no requirement that <tt>T</tt> is <tt>CopyInsertable</tt> into <tt>X</tt>. -</p> - -<p><i>[2012, Portland: Move to Tentatively NAD]</i></p> - -<p> -Howard notes that this may be a difficult requirement for <tt>std::array</tt> -</p> - -<p> -We already have this requirement for allocator aware containers, and -<tt>std::array</tt> already adds the appropriate extra requirement. -</p> - -<p> -We say the necessary things in the necessary places, but the container requirements -continue to cause confusion in where we sometimes say things. Consensus is that -this issue remains NAD though. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3376.</p> - -<ol> -<li><p>Change Table 96 — "Container requirements" in 23.2.1 [container.requirements.general]:</p> - -<table border="1"> -<caption>Table 96 — Container requirements</caption> - -<tr> -<th>Expression</th> -<th>Return type</th> -<th>Operational semantics</th> -<th>Assertion/note pre-/post-condition</th> -<th>Complexity</th> -</tr> - -<tr> -<td> -<tt>r = a</tt> -</td> -<td> -<tt>X&</tt> -</td> -<td> -<tt></tt> -</td> -<td> -<ins><i>Requires</i>: <tt>T</tt> is <tt>CopyInsertable</tt> into <tt>X</tt>.</ins><br/> -post: <tt>r == a.</tt> -</td> -<td> -linear -</td> -</tr> - -</table> - -</li> -</ol> - - - - - - - -<hr> -<h3><a name="2171"></a>2171. "swappable" undefined for swapping lvalue and rvalue</h3> -<p><b>Section:</b> 17.6.3.2 [swappable.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Robert Shearer <b>Opened:</b> 2012-07-24 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#swappable.requirements">issues</a> in [swappable.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -Paragraph 17.6.3.2 [swappable.requirements] p4 states: -</p> -<blockquote><p> -An rvalue or lvalue <tt>t</tt> is <em>swappable</em> if and only if <tt>t</tt> is swappable with any rvalue or lvalue, -respectively, of type <tt>T</tt>. -</p></blockquote> -<p> -This paragraph seems to establish two disjoint definitions of "swappable" — one for lvalues and one -for rvalues — with neither definition including the case of swapping an rvalue with an lvalue. -<p/> -Resolution proposal: -<p/> -Delete the word "respectively". -</p> - -<p><i>[ -2012-10 Portland: Close as NAD -]</i></p> - - -<p> -The current wording does intentionally specify two families of 'swappable' behaviors, for lvalues -and for rvalues, and not for mixed behavior. The need to support rvalues is for types like -<tt>vector<bool>::reference</tt>. Likewise, library types like <tt>string</tt> provide a -<tt>swap</tt> for values, but not a mixed-mode <tt>swap</tt> between lvalues and rvalues, which -were deliberately removed from C++11 after initally being part of the standard. -</p> - -<p> -Accepting this resolution would break the library specification, as no current library type would -meet the new requirements. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3376.</p> - -<p>Change 17.6.3.2 [swappable.requirements] p4 as indicated:</p> - -<blockquote><p> -An rvalue or lvalue <tt>t</tt> is <em>swappable</em> if and only if <tt>t</tt> is swappable with any rvalue or -lvalue <del>, respectively,</del> of type <tt>T</tt>. -</p></blockquote> - - - - - - -<hr> -<h3><a name="2204"></a>2204. <tt>reverse_iterator</tt> should not require a second copy of the base iterator</h3> -<p><b>Section:</b> 24.5.1.3.4 [reverse.iter.op.star] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> David Abrahams <b>Opened:</b> 2012-10-30 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -This note in 24.5.1.3.4 [reverse.iter.op.star]/2: -</p> -<blockquote> - [ <i>Note</i>: This operation must use an auxiliary member variable rather than a - temporary variable to avoid returning a reference that persists beyond the - lifetime of its associated iterator. (See 24.2.) —<i>end note</i> ] -</blockquote> -<p> -is incorrect because such iterator implementations are ruled out by -24.2.5 [forward.iterators]/6, where it says: -</p> -<blockquote> - If <tt>a</tt> and <tt>b</tt> are both dereferenceable, then <tt>a == b</tt> if and only if <tt>*a</tt> and - <tt>*b</tt> are bound to the same object. -</blockquote> - -<p><i>[2013-04-20, Bristol]</i></p> - - -<p> -Alisdair: sugested to strike the "exposition only" member. -<p/> -Daniel: we must check that it wouldn't conflict with a previous solution to another issue. -<p/> -Dietmar: This is an issue but the proposing word is not correct. When we have proxies inside the sequence. -<p/> -Solution: NAD thanks to a contrieved example by Dietmar. -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -Strike the note, 24.5.1.3.4 [reverse.iter.op.star]/2: -</p> - -<blockquote> - <del>[ <i>Note</i>: This operation must use an auxiliary member variable rather than a - temporary variable to avoid returning a reference that persists beyond the - lifetime of its associated iterator. (See 24.2.) —<i>end note</i> ]</del> -</blockquote> - - - - - - -<hr> -<h3><a name="2251"></a>2251. C++ library should define <tt>ssize_t</tt></h3> -<p><b>Section:</b> 18.2 [support.types] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Matt Austern <b>Opened:</b> 2013-04-19 <b>Last modified:</b> 2015-05-22</p> -<p><b>View all other</b> <a href="lwg-index.html#support.types">issues</a> in [support.types].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> - -<p> -The C++ standard library defines <tt>size_t</tt>, a typedef for an implementation defined unsigned integer type -that can represent the sizes of objects. The POSIX standard augments this with <tt>ssize_t</tt>, a typedef for a -signed integer type that corresponds to <tt>size_t</tt>. -<p/> -The <tt>ssize_t</tt> typedef is useful — useful enough that the C++ standard even refers to it. (In a -non-normative footnote in 27.5.2 [stream.types].) Also, lots of OS vendors add it to their headers anyway, -even though it isn't part of the C or C++ standards, because those vendors are trying to define headers that -conform to multiple standards at once. We should make users' and implementers' lives easier by adding -<tt>ssize_t</tt> to 18.2 [support.types]. -</p> - -<p><i>[2013-09-29, Suggested wording from Jayson Oldfather]</i></p> - -<p> -I decided to use the phrase to describe <tt>ssize_t</tt> below because of the text describing it in the -<a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/sys_types.h.html#tag_13_67">POSIX</a> standard. -In it, it describes <tt>ssize_t</tt> with the value range of <tt>[-1,{SSIZE_MAX}]</tt>. -<tt>SSIZE_MAX</tt> is specified in the <a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/limits.h.html#tag_13_24">POSIX</a> -standard as a minimum value of <tt>_POSIX_SSIZE_MAX</tt>. This macro is referenced in the wording below. -</p> - -<p><i>[Lenexa 2015-05-05: NAD - no consensus for a change]</i></p> - -<p>Billy : ssize_t that was promised to be signed, was based on rsize_t from safe secure C</p> -<p>NM : ssize_t s ptrdif_t</p> -<p>Z : ptrdiff_t is full range, ssize_t has only -1 as negative value</p> -<p>Billy : motivations for ptrdiff_T, ssize_t and rsize_T all fuzzy. - Reads rsize max -</p> -<p>NM : ptrdiff_T not big enough to rep difference of pointers anymore</p> -<p>STL : description incorporates posixisms</p> -<p>Billy : Don't need it</p> -<p>NM : rather remove it from footnote</p> -<p>Z : Name has precise meaning</p> -<p>STL : everyone understands ptrdiff_t is signed counterpart to size_t</p> -<p>Billy : Not in all implementations anymore</p> -<p>DK : footnote says something different from ...</p> -<p>Z/NM : off_t historically tainted</p> -<p>STL : we have a type trait to make signed version of size_t. we should just use that</p> -<p>MC : NAD; is feature request</p> -<p>TP : It's not cstdsef</p> - - - -<p><b>Proposed resolution:</b></p> -<ol> -<li> -<p> -Ammend 18.2 [support.types], Table 30 as indicated: -</p> - -<blockquote> -<table border="1"> -<caption>Table 30 — Header <tt><cstddef></tt> synopsis</caption> -<tr> -<th>Type</th> -<th>Name(s)</th> -</tr> - -<tr> -<td> -<b>Macros:</b> -</td> -<td> -<tt>NULL offset_t</tt> -</td> -</tr> - -<tr> -<td> -<b>Types:</b> -</td> -<td> -<tt>ptrdiff_t <ins>ssize_t</ins> size_t max_align_t nullptr_t</tt> -</td> -</tr> -</table> -</blockquote> - -<p>Add the following paragraph to describe <tt>ssize_t</tt></p> -<blockquote><p><ins> --?- The type <tt>ssize_t</tt> is an implementation-defined signed integer type that shall contain the minimum range -<tt>[-1, {SSIZE_MAX}]</tt> where <tt>SSIZE_MAX</tt> is specified at a minimum of <tt>_POSIX_SSIZE_MAX</tt>.</ins> -</p></blockquote> -<p>Ammend p7 as follows:</p> -<blockquote><p> --7- [<i>Note:</i> It is recommended that implementations choose types for <tt>ptrdiff_t<ins>, ssize_t,</ins></tt> and <tt>size_t</tt> whose integer conversion ranks …</p></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="2270"></a>2270. Inconsistent <tt>to_string</tt> overloads</h3> -<p><b>Section:</b> 21.5 [string.conversions] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Raf Schietekat <b>Opened:</b> 2013-07-02 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#string.conversions">issues</a> in [string.conversions].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -For internal consistency, <tt>to_string()</tt> should either list all relevant types (including <tt>bool</tt>, <tt>char</tt>, etc.), -or only those that are the destination types of integral or floating-point promotion (<tt>float</tt> not being among them). -<p/> -A defensible reason for having (or rather keeping) the <tt>float</tt> overloads anyway could be to exactly mirror the adjacent -sets of <tt>stoX()</tt> function overloads (even without round-trip fidelity for floating-point numbers). -<p/> -Unfortunately, that reveals a bigger issue than redundant overloads: the glaring and indefensible omission of an overloaded -function <tt>stoui()</tt>. Adding that is not as trivial as removing redundant overloads, of course, because it requires -everybody to take action. Still, it is the preferable remedy for the present situation. -<p/> -As far as I can tell from easily accessible information, C++ has already created the precedent with <tt>stoi()</tt>, which -is not the equivalent of a pair of functions <tt>strtoi()</tt>/<tt>wcstoi()</tt> in C, but it would be if such functions -existed. The function <tt>atoi()</tt> may look similar, but it does not qualify because it is as different from a -hypothetical <tt>strtoi()</tt> as <tt>atol()</tt> currently is from <tt>strtol()</tt>, with the latter two both Standard C. -It is only logical to act on this one-sided precedent by completing the set. Whether or not Standard C leads the way -(or follows suit) is immaterial, but an invitation could be extended. -</p> - -<p><i>[2013-09 Chicago]</i></p> - -<p> -These overloads were very carefully and experimentally determined to be the minimal set, when all (known) promotion and -conversion scenarios were considered. Removing superfluous-looking overloads is likely to result in ambiguities. -</p> - - - -<p><b>Proposed resolution:</b></p> - -<p>This wording is relative to N3691.</p> - -<ol> -<li><p>Modify 21.3 [string.classes], header <tt><string></tt> synopsis, as indicated:</p> - -<blockquote><pre> -#include <initializer_list> - -namespace std { - […] - string to_string(int val); - string to_string(unsigned val); - string to_string(long val); - string to_string(unsigned long val); - string to_string(long long val); - string to_string(unsigned long long val); - <del>string to_string(float val);</del> - string to_string(double val); - string to_string(long double val); - […] - - […] - wstring to_wstring(int val); - wstring to_wstring(unsigned val); - wstring to_wstring(long val); - wstring to_wstring(unsigned long val); - wstring to_wstring(long long val); - wstring to_wstring(unsigned long long val); - <del>wstring to_wstring(float val);</del> - wstring to_wstring(double val); - wstring to_wstring(long double val); - […] -} -</pre></blockquote> -</li> - -<li><p>Modify 21.5 [string.conversions] p7+14 as indicated:</p> - -<blockquote> -<pre> -string to_string(int val); -string to_string(unsigned val); -string to_string(long val); -string to_string(unsigned long val); -string to_string(long long val); -string to_string(unsigned long long val); -<del>string to_string(float val);</del> -string to_string(double val); -string to_string(long double val); -</pre> -<blockquote> -<p> --7- <i>Returns:</i> Each function returns a <tt>string</tt> object holding the character representation of the value of -its argument that would be generated by calling <tt>sprintf(buf, fmt, val)</tt> with a format specifier of -<tt>"%d"</tt>, <tt>"%u"</tt>, <tt>"%ld"</tt>, <tt>"%lu"</tt>, <tt>"%lld"</tt>, <tt>"%llu"</tt>, <del><tt>"%f"</tt>,</del> -<tt>"%f"</tt>, or <tt>"%Lf"</tt>, respectively, where <tt>buf</tt> designates an internal character buffer of sufficient size. -<p/> -[…] -</p> -</blockquote> -<pre> -wstring to_wstring(int val); -wstring to_wstring(unsigned val); -wstring to_wstring(long val); -wstring to_wstring(unsigned long val); -wstring to_wstring(long long val); -wstring to_wstring(unsigned long long val); -<del>wstring to_wstring(float val);</del> -wstring to_wstring(double val); -wstring to_wstring(long double val); -</pre> -<blockquote> -<p> --14- <i>Returns:</i> Each function returns a <tt>wstring</tt> object holding the character representation of the value of -its argument that would be generated by calling <tt>swprintf(buf, buffsz, fmt, val)</tt> with a format specifier of -<tt>L"%d"</tt>, <tt>L"%u"</tt>, <tt>L"%ld"</tt>, <tt>L"%lu"</tt>, <tt>L"%lld"</tt>, <tt>L"%llu"</tt>, <del><tt>L"%f"</tt>,</del> -<tt>L"%f"</tt>, or <tt>L"%Lf"</tt>, respectively, where <tt>buf</tt> designates an internal character buffer of sufficient -size <tt>buffsz</tt>. -</p> -</blockquote> -</blockquote> -</li> -</ol> - - - - - - -<hr> -<h3><a name="2279"></a>2279. Carefully state effects of <tt>list::splice</tt> function</h3> -<p><b>Section:</b> 23.3.5.5 [list.ops], 23.3.4.6 [forwardlist.ops] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Arseny Klimovsky <b>Opened:</b> 2013-08-15 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#list.ops">issues</a> in [list.ops].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I think that the effects of <tt>list::splice</tt> function should be stated more carefully. -<p/> -Function transferring a single element is described now in the following way (23.3.5.5 [list.ops] p7): -</p> - -<blockquote> -<pre> -void splice(const_iterator position, list& x, const_iterator i); -void splice(const_iterator position, list&& x, const_iterator i); -</pre> -<blockquote> -<p> -<i>Effects:</i> Inserts an element pointed to by <tt>i</tt> from list <tt>x</tt> before position and removes the element from -<tt>x</tt>. The result is unchanged if <tt>position == i</tt> or <tt>position == ++i</tt>. Pointers and references to <tt>*i</tt> -continue to refer to this same element but as a member of <tt>*this</tt>. Iterators to <tt>*i</tt> (including <tt>i</tt> itself) -continue to refer to the same element, but now behave as iterators into <tt>*this</tt>, not into <tt>x</tt>. -</p> -</blockquote> -</blockquote> - -<p> -But it is incorrect to talk about <tt>operator==</tt> for iterators that are not from the same container (after acceptance of -<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3066.html">N3066</a>, 24.2.5 [forward.iterators] p2). -So, the text operates with an undefined behaviour. -</p> - -<p> -One is formally allowed to have list implementation where two iterators from different lists return true to <tt>operator==</tt>. -For example, this can only happen to non-dereferenceable iterators, and <tt>position</tt> and <tt>++i</tt> can be -non-dereferenceable. So, literally according to the standard, it is not allowed in this implementation to transfer -such elements with <tt>splice</tt> function. -</p> - -<p><i>[2013-09 Chicago (late night issues)]</i></p> - -<p> -Moved to NAD. -</p> -<p> -The condition under which the <tt>list</tt> is unchanged is not program code, so there is no undefined behavior to protect against. -Rather, the precondition that the evaluation can be performed is implicit if determining when the condition applies. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3691.</p> - -<ol> -<li><p>Modify 23.3.4.6 [forwardlist.ops] p6 as indicated:</p> - -<blockquote> -<pre> -void splice_after(const_iterator position, forward_list& x, const_iterator i); -void splice_after(const_iterator position, forward_list&& x, const_iterator i); -</pre> -<blockquote> -<p> -[…] -<p/> --6- <i>Effects:</i> Inserts the element following <tt>i</tt> into <tt>*this</tt>, following <tt>position</tt>, -and removes it from <tt>x</tt>. The result is unchanged if <ins><tt>&x == this</tt> and the following -condition is satisfied:</ins> <tt>position == i</tt> or <tt>position == ++i</tt>. Pointers and references to -<tt>*++i</tt> continue to refer to the same element but as a member of <tt>*this</tt>. Iterators to <tt>*++i</tt> -continue to refer to the same element, but now behave as iterators into <tt>*this</tt>, not into <tt>x</tt>. -</p> -</blockquote> -</blockquote> -</li> - -<li><p>Modify 23.3.5.5 [list.ops] p7 as indicated:</p> - -<blockquote> -<pre> -void splice(const_iterator position, list& x, const_iterator i); -void splice(const_iterator position, list&& x, const_iterator i); -</pre> -<blockquote> -<p> --7- <i>Effects:</i> Inserts an element pointed to by <tt>i</tt> from list <tt>x</tt> before position and removes -the element from <tt>x</tt>. The result is unchanged if <ins><tt>&x == this</tt> and the following -condition is satisfied:</ins> <tt>position == i</tt> or <tt>position == ++i</tt>. Pointers and references to -<tt>*i</tt> continue to refer to this same element but as a member of <tt>*this</tt>. Iterators to <tt>*i</tt> -(including <tt>i</tt> itself) continue to refer to the same element, but now behave as iterators into <tt>*this</tt>, -not into <tt>x</tt>. -</p> -</blockquote> -</blockquote> -</li> - -</ol> - - - - - -<hr> -<h3><a name="2281"></a>2281. C99 cross-reference typo in [using.linkage]</h3> -<p><b>Section:</b> 17.6.2.3 [using.linkage] <b>Status:</b> <a href="lwg-active.html#NAD Editorial">NAD Editorial</a> - <b>Submitter:</b> Chris Sharpe <b>Opened:</b> 2013-08-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#using.linkage">issues</a> in [using.linkage].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p> -<p><b>Discussion:</b></p> -<p> -There is a footnote at section 17.6.2.3 [using.linkage]/2 that reads: -</p> -<blockquote><p> -"The only reliable way to declare an object or function signature from the Standard C library is by including -the header that declares it, notwithstanding the latitude granted in 7.1.7 of the C Standard." -</p></blockquote> -<p> -There is no section 7.1.7 in the C99 Standard (or C11 final draft). I think the relevant section is: -</p> -<blockquote><p> -"Provided that a library function can be declared without reference to any type defined in a header, it is also -permissible to declare the function and use it without including its associated header." -</p></blockquote> -<p> -at 7.1.4/2 from C99. -</p> - -<p><i>[2013-09 Chicago]</i></p> - -<p> -Moved to NAD Editorial. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3691.</p> - -<ol> -<li><p>Edit footnote 182, 17.6.2.3 [using.linkage] as indicated:</p> - -<blockquote> -<p> -The only reliable way to declare an object or function signature from the Standard C library is by including the header -that declares it, notwithstanding the latitude granted in <del>7.1.7</del><ins>7.1.4</ins> of the C Standard. -</p> -</blockquote> -</li> - -</ol> - - - - - -<hr> -<h3><a name="2297"></a>2297. [CD] Missing type requirements for <tt>std::exchange</tt></h3> -<p><b>Section:</b> 20.2.3 [utility.exchange] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Alisdair Meredith <b>Opened:</b> 2013-09-22 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#utility.exchange">issues</a> in [utility.exchange].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses GB 5</b></p> - -<p> -The wording describes example code including the call of a move constructor, but there is no requirement -stated that <tt>T</tt> be move constructible. -<p/> -We would like to add a new Para 1 before existing paragraph: -</p> -<blockquote><p> -<i>Requires:</i> Type <tt>T</tt> shall be <tt>MoveConstructible</tt> (Table 20) and <tt>MoveAssignable</tt> (Table 22). -</p></blockquote> - -<p> -However the <tt>MoveAssignable</tt> concept currently does not cover cases where the source and destination types may differ. -</p> - -<p><i>[2013-09 Chicago]</i></p> - -<p> -The requirements are implicit according to 17.5.1.4 [structure.specifications]p4. There is no desire to redundantly -repeat a set of requirements. -</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2302"></a>2302. Passing null pointer to placement new</h3> -<p><b>Section:</b> 18.6.1.3 [new.delete.placement] <b>Status:</b> <a href="lwg-active.html#NAD">Pending NAD</a> - <b>Submitter:</b> Marc Glisse <b>Opened:</b> 2013-09-12 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#new.delete.placement">issues</a> in [new.delete.placement].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Pending NAD">Pending NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Based on <a href="http://stackoverflow.com/questions/17571103/passing-null-pointer-to-placement-new">this discussion</a> -and as discussed in <a href="http://accu.org/cgi-bin/wg21/message?wg=core&msg=23998">c++std-core-23998</a> and -<a href="http://accu.org/cgi-bin/wg21/message?wg=lib&msg=34442">c++std-lib-34442</a>, calling placement new currently forces the -compiler to check if the pointer is null before initializing the object (a non-negligible cost). It seems many people were not -aware of this and they consider it a user error to pass a null pointer to it. -<p/> -Proposed resolution: for <tt>operator new</tt> and <tt>operator new[]</tt>, add: -</p> -<blockquote><p> -<i>Requires:</i> <tt>ptr</tt> shall not be a null pointer. -</p></blockquote> - -<p><i>[2014-02-15 post-Issaquah session : move to Tentatively NAD]</i></p> - -<p> -AJM to supply the rationale... -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3691.</p> - -<ol> -<li><p>Change 18.6.1.3 [new.delete.placement] as indicated:</p> - -<blockquote> -<pre> -void* operator new(std::size_t size, void* ptr) noexcept; -</pre> -<blockquote> -<p> -<ins>-?- <i>Requires:</i> <tt>ptr</tt> shall not be a null pointer.</ins> -<p/> --2- <i>Returns:</i> <tt>ptr</tt>. -<p/> --3- <i>Remarks:</i> Intentionally performs no other action. -<p/> --4- [<i>Example:</i> This can be useful for constructing an object at a known address: -</p><blockquote><pre> -void* place = operator new(sizeof(Something)); -Something* p = new (place) Something(); -</pre></blockquote> -<p> -— <i>end example</i>] -</p> -</blockquote> -</blockquote> -<blockquote> -<pre> -void* operator new[](std::size_t size, void* ptr) noexcept; -</pre> -<blockquote> -<p> -<ins>-?- <i>Requires:</i> <tt>ptr</tt> shall not be a null pointer.</ins> -<p/> --5- <i>Returns:</i> <tt>ptr</tt>. -<p/> --6- <i>Remarks:</i> Intentionally performs no other action. -</p> -</blockquote> -</blockquote> -</li> - -</ol> - - - - - -<hr> -<h3><a name="2305"></a>2305. [fund.ts] <tt>optional</tt> forwarding construction/assignment</h3> -<p><b>Section:</b> X [optional.object.ctor] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Cassio Neri <b>Opened:</b> 2013-09-23 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p><b>Addresses: fund.ts</b></p> - -<p> -Consider: -</p> -<blockquote><pre> -struct foo { - foo(std::initializer_list<int>&); // 1 - foo(const std::initializer_list<int>&); // 2 - foo(std::initializer_list<int>&&); // 3 - foo(const std::initializer_list<int>&&); // 4 -}; - -std::initializer_list<int> il{0, 1, 2}; - -foo foo_0{1, 2, 3}; // calls 3 -foo foo_1{il}; // calls 1 -foo foo_2((const std::initializer_list<int>&) il); // calls 2 -foo foo_3{(std::initializer_list<int>&&) il}; // calls 3 -foo foo_4((const std::initializer_list<int>&&) il); // calls 4 -</pre></blockquote> -<p> -Although the constructors of <tt>foo</tt> are unusual (<tt>initializer_list</tt>s are <i>normally</i> passed by -value) users of <tt>optional</tt> could naturally expect perfect forwarding of <tt>initializer_list</tt>s. However, -all lines below end up calling 1. -</p> -<blockquote><pre> -optional<foo> opt0{in_place, {1, 2, 3}}; -optional<foo> opt1{in_place, il}; -optional<foo> opt3{in_place, (const std::initializer_list<int>&) il}; -optional<foo> opt2{in_place, (std::initializer_list<int>&&) il}; -optional<foo> opt4{in_place, (const std::initializer_list<int>&&) il}; - -opt0.emplace({1, 2, 3}); -opt0.emplace(il); -opt0.emplace((const std::initializer_list<int>&) il); -opt0.emplace((std::initializer_list<int>&&) il); -opt0.emplace((const std::initializer_list<int>&&) il); -</pre></blockquote> -<p> -The constructor -</p> -<blockquote><pre> -template <class... Args> constexpr explicit optional(in_place_t, Args&&... args); -</pre></blockquote> -<p> -can handle all constructor calls above, except the one taking <tt>{1, 2, 3}</tt>. Hence, a simple -<ins>modification</ins> of -</p> -<blockquote><pre> -template <class U, class... Args> -constexpr explicit optional(in_place_t, initializer_list<U><ins>&&</ins> il, Args&&... args); -</pre></blockquote> -<p> -allows perfect forwarding of <tt>std::initializer_list<U></tt>s to be complete. -</p> - -<p><i>[2014-06-06 pre-Rapperswil]</i></p> - -<p> -This issue has been reopened as fundamentals-ts. -</p> - -<p><i>[2014-06-17, Rapperswil]</i></p> - -<p> -Move to NAD -</p> - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3691.</p> - -<ol> -<li><p>Change X [optional.object.ctor] as indicated:</p> - -<blockquote><pre> -template <class U, class... Args> -constexpr explicit optional(in_place_t, initializer_list<U><ins>&&</ins> il, Args&&... args); -</pre><blockquote> -<p> --27- <i>Requires</i>: <tt>is_constructible<T, initializer_list<U>&<ins>&</ins>, Args&&...>::value</tt> is <tt>true.</tt> -<p/> --28- <i>Effects</i>: Initializes the contained value as if constructing an object of type <tt>T</tt> with the arguments -<tt><del>il</del><ins>std::move(il)</ins></tt>, <tt>std::forward<Args>(args)...</tt>. -<p/> -[…] -<p/> -<del>-31- <i>Remarks</i>: The function shall not participate in overload resolution unless -<tt>is_constructible<T, initializer_list<U>&, Args&&...>::value</tt> is <tt>true</tt>.</del> -</p> -</blockquote> -</blockquote> -</li> -<li><p>Change X [optional.object.assign] as indicated:</p> - -<blockquote><pre> -template <class U, class... Args> -void optional<T>::emplace(initializer_list<U><ins>&&</ins> il, Args&&... args); -</pre><blockquote> -<p> --27- <i>Requires</i>: <tt>is_constructible<T, initializer_list<U>&<ins>&</ins>, Args&&...>::value</tt> is <tt>true.</tt> -<p/> --28- <i>Effects</i>: Calls <tt>*this = nullopt</tt>. Then initializes the contained value as if constructing an object of -type <tt>T</tt> with the arguments <tt><del>il</del><ins>std::move(il)</ins></tt>, <tt>std::forward<Args>(args)...</tt>. -<p/> -[…] -<p/> -<del>-32- <i>Remarks</i>: This function shall not participate in overload resolution unless -<tt>is_constructible<T, initializer_list<U>&, Args&&...>::value</tt> is <tt>true.</tt></del> -</p> -</blockquote> -</blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="2311"></a>2311. Allocator requirements should be further minimized</h3> -<p><b>Section:</b> 17.6.3.5 [allocator.requirements] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2013-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View other</b> <a href="lwg-index-open.html#allocator.requirements">active issues</a> in [allocator.requirements].</p> -<p><b>View all other</b> <a href="lwg-index.html#allocator.requirements">issues</a> in [allocator.requirements].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -C++11's minimized allocator requirements are great, but they're still requiring more things from users than absolutely necessary. -</p> -<ul> -<li><p> -They require <tt>X::value_type</tt>, but that can be deduced from <tt>SomeAllocator<T, Args></tt>. -</p></li> -<li><p> -They require <tt>a1 == a2</tt>, but that could default to <tt>true</tt> as most allocators are stateless. -</p></li> -<li><p> -They require <tt>a1 != a2</tt>, but if we start requiring STL implementations to go through <tt>allocator_traits</tt> -to provide an <tt>op==</tt> default, we won't need to require <tt>op!=</tt> from users at all. (<tt>std::allocator</tt>, -of course, would continue to provide <tt>op!=</tt>. Note that this is analogous to <tt>reference</tt>/<tt>const_reference</tt> — -<tt>std::allocator</tt> still provides them, but we don't require them from users, and in fact we don't require them to be -consistent or meaningful if present.) -</p></li> -<li><p> -They require <tt>a == b</tt> and <tt>a != b</tt>. This requirement was not present in C++98/03, it is not necessary -(<tt>a == b</tt> is always required to be equivalent to rebind-then-compare), and STL implementations don't even need -to compare allocators of different types directly. -</p></li> -</ul> - -<p><i>[2014-02-14 Issaquah: Close as NAD]</i></p> - -<p> -Different vendors rely on each of the different elements suggested to be removed. -</p> -<p> -While <tt>value_type</tt> my be deduced as suggested, far too much wording relies on it being available, -and the standard churn is likely to be much harder than presented here. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3691.</p> - -<ol> -<li><p>Change in 17.6.3.5 [allocator.requirements], Table 28 — "Allocator requirements" as indicated:</p> - -<blockquote> -<table border="1"> -<caption>Table 28 — Allocator requirements (continued)</caption> -<tr> -<th>Expression</th> -<th>Return type</th> -<th>Assertion/note pre-/post-condition</th> -<th>Default</th> -</tr> - -<tr> -<td colspan="4" align="center"> -<tt>…</tt> -</td> -</tr> - -<tr> -<td> -<tt>X::value_type</tt> -</td> -<td> -Identical to <tt>T</tt> -</td> -<td> - -</td> -<td> -<ins>See Note B, below.</ins> -</td> -</tr> - -<tr> -<td colspan="4" align="center"> -<tt>…</tt> -</td> -</tr> - -<tr> -<td> -<tt>a1 == a2</tt> -</td> -<td> -<tt>bool</tt> -</td> -<td> -returns <tt>true</tt> only if storage<br/> -allocated from each can be<br/> -deallocated via the other.<br/> -<tt>operator==</tt> shall be reflexive,<br/> -symmetric, and transitive, and<br/> -shall not exit via an exception.<br/> -</td> -<td> -<ins><tt>true</tt></ins> -</td> -</tr> - -<tr> -<td> -<del><tt>a1 != a2</tt></del> -</td> -<td> -<del><tt>bool</tt></del> -</td> -<td> -<del>same as <tt>!(a1 == a2)</tt></del> -</td> -<td> - -</td> -</tr> - -<tr> -<td> -<del><tt>a == b</tt></del> -</td> -<td> -<del><tt>bool</tt></del> -</td> -<td> -<del>same as <tt>a ==<br/> -Y::rebind<T>::other(b)</tt></del> -</td> -<td> - -</td> -</tr> - -<tr> -<td> -<del><tt>a != b</tt></del> -</td> -<td> -<del><tt>bool</tt></del> -</td> -<td> -<del>same as <tt>!(a == b)</tt></del> -</td> -<td> - -</td> -</tr> - -<tr> -<td colspan="4" align="center"> -<tt>…</tt> -</td> -</tr> - -<tr> -<td> -<tt>X a(b);</tt> -</td> -<td> - -</td> -<td> -Shall not exit via an exception.<br/> -post: <tt>Y(a) == b</tt>, <tt>a == X(b)</tt> -</td> -<td> - -</td> -</tr> - -<tr> -<td colspan="4" align="center"> -<tt>…</tt> -</td> -</tr> - -<tr> -<td> -<tt>X a(move(b));</tt> -</td> -<td> - -</td> -<td> -Shall not exit via an exception.<br/> -post: <tt>a</tt> equals the prior value of <tt>X(b)</tt>. -</td> -<td> - -</td> -</tr> - -<tr> -<td colspan="4" align="center"> -<tt>…</tt> -</td> -</tr> - -</table> -</blockquote> - -</li> - -<li><p>After 17.6.3.5 [allocator.requirements] p3, add a new paragraph:</p> - -<blockquote> -<p> -<ins>Note B: If <tt>Allocator</tt> is a class template instantiation of the form <tt>SomeAllocator<T, Args></tt>, -where <tt>Args</tt> is zero or more type arguments, and <tt>Allocator</tt> does not supply a nested type named <tt>value_type</tt>, -the standard <tt>allocator_traits</tt> template uses <tt>T</tt> in place of <tt>Allocator::value_type</tt> by default. -For allocator types that are not template instantiations of the above form, no default is provided.</ins> -</p> -</blockquote> -</li> - -<li><p>In the example provided in 17.6.3.5 [allocator.requirements]/5, delete as indicated:</p> - -<blockquote> -<pre> -template <class Tp> -struct SimpleAllocator { - <del>typedef Tp value_type;</del> - SimpleAllocator(ctor args); - template <class T> SimpleAllocator(const SimpleAllocator<T>& other); - Tp *allocate(std::size_t n); - void deallocate(Tp *p, std::size_t n); -}; - -<del>template <class T, class U> -bool operator==(const SimpleAllocator<T>&, const SimpleAllocator<U>&); -template <class T, class U> -bool operator!=(const SimpleAllocator<T>&, const SimpleAllocator<U>&);</del> -</pre> -</blockquote> - -</li> - -<li><p>Edit 20.7.8 [allocator.traits]p1, class template <tt>allocator_traits</tt> synopsis, as indicated:</p> - -<blockquote><pre> -namespace std { - template <class Alloc> struct allocator_traits { - typedef Alloc allocator_type; - - typedef <del>typename Alloc::value_type</del><ins><i>see below</i></ins> value_type; - - […] - - static Alloc select_on_container_copy_construction(const Alloc& rhs); - - <ins>static bool equal(const Alloc& a1, const Alloc& a2) noexcept;</ins> - }; -} -</pre></blockquote> -</li> - -<li><p>At the beginning of 20.7.8.1 [allocator.traits.types], add a new paragraph:</p> - -<blockquote><pre> -<ins>typedef <i>see below</i> value_type;</ins> -</pre><blockquote> -<p> -<ins><i>Type:</i> <tt>Alloc::value_type</tt> if such a type exists; otherwise, <tt>T</tt> if <tt>Alloc</tt> is a class template -instantiation of the form <tt>Alloc<T, Args></tt>, where <tt>Args</tt> is zero or more type arguments; otherwise, the program -is ill-formed.</ins> -</p> -</blockquote></blockquote> -</li> - -<li><p>At the end of 20.7.8.2 [allocator.traits.members], add a new paragraph:</p> - -<blockquote><pre> -<ins>static bool equal(const Alloc& a1, const Alloc& a2) noexcept;</ins> -</pre><blockquote> -<p> -<ins>-?- <i>Returns:</i> <tt>a1 == a2</tt> if that expression is well-formed; otherwise, <tt>true</tt>.</ins> -</p> -</blockquote></blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="2327"></a>2327. Non-power-of-two URNGs should be forbidden</h3> -<p><b>Section:</b> 26.5.1.3 [rand.req.urng] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2013-09-21 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.req.urng">issues</a> in [rand.req.urng].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -26.5.1.3 [rand.req.urng] allows URNGs with non-power-of-two (NPOT) ranges, like <tt>[0, 1729]</tt>. This is unnecessarily permissive -(I cannot imagine a realistic source of randomness that would generate such a range) and has real costs for implementers, as -<tt>uniform_int_distribution</tt> must be prepared to accept such URNGs. The most efficient way to accumulate randomness is to -concatenate random bits, so NPOT randomness is not just useless, it is actively harmful (to avoid bias, if a URNG generates a -random number outside of a power-of-two range, the number must be discarded). -<p/> -Forbidding NPOT URNGs wouldn't affect users, and would simplify Standard Library implementations. It would be nice to require -<tt>min()</tt> to be <tt>0</tt>, but this is not necessary; it is simple for implementations to say <tt>g() - G::min()</tt> and -this will optimize away if <tt>min()</tt> is <tt>0</tt>. (It is vaguely plausible for a URNG to have a nonzero minimum; I can -imagine something that simply masks off low-order bits without shifting the rest downwards.) What is important is for the entire -range to have a power-of-two width; <tt>[1729, 1984]</tt> is acceptable as its size is 256. -</p> - -<p><i>[2013-10-12: Howard presents a counterexample]</i></p> - - -<p> -Consider: -</p> -<blockquote><pre> -#include <random> -#include <string> -#include <iostream> - -template <class Int> -bool is_power_2m1(Int i) -{ - return (i & (i + 1)) == 0; -} - -template <class URNG> -void test(const std::string& urng) -{ - using namespace std; - typename URNG::result_type rng = URNG::max() - URNG::min(); - if (!is_power_2m1(rng)) - { - cout << hex; - cout << urng << " : min = " << URNG::min() << ", max = " << URNG::max() - << ", max-min = " << rng << '\n'; - } -}; - -int main() -{ - using namespace std; - test<minstd_rand0>("minstd_rand0"); - test<minstd_rand>("minstd_rand"); - test<mt19937>("mt19937"); - test<mt19937_64>("mt19937_64"); - test<ranlux24_base>("ranlux24_base"); - test<ranlux48_base>("ranlux48_base"); - test<ranlux24>("ranlux24"); - test<ranlux48>("ranlux48"); - test<knuth_b>("knuth_b"); -} -</pre></blockquote> - -<p> -Which for me outputs: -</p> - -<blockquote><pre> -minstd_rand0 : min = 1, max = 7ffffffe, max-min = 7ffffffd -minstd_rand : min = 1, max = 7ffffffe, max-min = 7ffffffd -knuth_b : min = 1, max = 7ffffffe, max-min = 7ffffffd -</pre></blockquote> - -<p> -We do not want to outlaw these three URNG's, and the proposed wording would do that. -</p> - -<p><i>[Issaquah 2014-02-10: Moved to NAD]</i></p> - -<p> -STL withdraws the issue, non-power-of-2 URNGs are used in the field, it is too late to consider removing them. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3691.</p> - -<ol> -<li><p>Add a new paragraph at the end of 26.5.1.3 [rand.req.urng] as indicated:</p> - -<blockquote> -<p> --3- The following relation shall hold: <tt>G::min() < G::max()</tt>. -<p/> -<ins>-?- <tt>G::max() - G::min()</tt> shall be 2<sup><tt>n</tt></sup> - 1 for some <tt>n > 0</tt>.</ins> -</p> -</blockquote> -</li> -</ol> - - - - - -<hr> -<h3><a name="2345"></a>2345. <tt>integer_sequence</tt> should have a self-typedef <tt>::type</tt></h3> -<p><b>Section:</b> 20.5.2 [intseq.intseq] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2013-11-01 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -20.10.3 [meta.help] says that <tt>integral_constant<T, v></tt> provides <tt>::value_type</tt> (for <tt>T</tt>) -and <tt>::type</tt> (for itself). -<p/> -20.5.2 [intseq.intseq] says that <tt>integer_sequence<T, I...></tt> provides <tt>::value_type</tt> (for <tt>T</tt>), -but nothing for itself. -<p/> -Self-typedefs can be useful when users create chains of derived classes, then want to get the Standard base type. -This is especially relevant to <tt>integer_sequence</tt>, as variadic templates encourage recursive inheritance. -</p> - -<p><i>[2014-02-13 Issaquah: Close as NAD]</i></p> - -<p> -AJM: My own implementation used a different alias for types representing parameter packs, and specifically -did <em>not</em> define <tt>type</tt>. I tried it both ways, and found bugs more quickly when <tt>type</tt> was -not defined. -</p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3797.</p> - -<ol> -<li><p>Edit 20.5.2 [intseq.intseq] as indicated:</p> - -<blockquote><pre> -namespace std { - template<class T, T... I> - struct integer_sequence { - typedef T value_type; - <ins>typedef integer_sequence<T, I...> type;</ins> - static constexpr size_t size() noexcept { return sizeof...(I); } - }; -} -</pre></blockquote> -</li> - -</ol> - - - - - - -<hr> -<h3><a name="2347"></a>2347. <tt>reverse_iterator::operator[]</tt> calls const version of <tt>current[]</tt></h3> -<p><b>Section:</b> 24.5.1.3.12 [reverse.iter.opindex] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Timo Bingmann <b>Opened:</b> 2013-11-11 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#reverse.iter.opindex">issues</a> in [reverse.iter.opindex].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Currently <tt>reverse_iterator::operator[]()</tt> returns "<tt>current[-n-1]</tt>" and has -an "<em>unspecified</em>" return type. -<p/> -When <tt>Iterator</tt> is a mutable random access iterator, the expression -"<tt>current[-n-1]</tt>" calls "<tt>Iterator::operator[] const</tt>", which returns a -const reference. This const reference cannot be converted back to a -mutable reference. -<p/> -This issue is related to the "<em>unspecified</em>" return value of -<tt>reverse_iterator::operator[]</tt>, see defect <a href="lwg-defects.html#386">386</a>. -<p/> -The -1 is due to "current" pointing one item beyond the -<tt>reverse_iterator</tt>'s real current value. -<p/> -The current libstdc++ implementation reads "<tt>*(current + n)</tt>" for -<tt>reverse_iterator::operator[]</tt>. -<p/> -This copied <tt>current</tt>, advances (backwards) via <tt>operator+</tt> and -dereferences. It bypasses the issues due to <tt>reverse_iterator::operator[]</tt> -being const by copying the iterator. -</p> - -<p><i>[2014-02-13 Issaquah : close as NAD]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3797.</p> - -<ol> -<li><p>Edit 24.5.1.1 [reverse.iterator], class template <tt>reverse_iterator</tt> synopsis, as indicated:</p> - -<blockquote><pre> -namespace std { - template <class Iterator> - class reverse_iterator : public - iterator<typename iterator_traits<Iterator>::iterator_category, - typename iterator_traits<Iterator>::value_type, - typename iterator_traits<Iterator>::difference_type, - typename iterator_traits<Iterator>::pointer, - typename iterator_traits<Iterator>::reference> { - public: - […] - <del><em>unspecified</em></del><ins>reference</ins> operator[](difference_type n) const; - […] - }; - […] -} -</pre></blockquote> -</li> - -<li><p>Edit 24.5.1.3.12 [reverse.iter.opindex] as indicated:</p> - -<blockquote><pre> -<del><em>unspecified</em></del><ins>reference</ins> operator[]( - typename reverse_iterator<Iterator>::difference_type n) const; -</pre><blockquote> -<p> --1- <i>Returns:</i> <tt><del>current[-n-1]</del><ins>*(current + n)</ins></tt>. -</p> -</blockquote></blockquote> -</li> - -</ol> - - - - - - -<hr> -<h3><a name="2351"></a>2351. Does <tt>.seed()</tt> completely reset state of engine?</h3> -<p><b>Section:</b> 26.5.3 [rand.eng] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Thomas Plum <b>Opened:</b> 2013-12-02 <b>Last modified:</b> 2015-05-22</p> -<p><b>View all other</b> <a href="lwg-index.html#rand.eng">issues</a> in [rand.eng].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -With regard to Random number engine class templates 26.5.3 [rand.eng], -the Standard can be read in two different ways: when the member function -</p> -<blockquote><pre> -.seed(result_type s = default_seed) -</pre></blockquote> -<p> -is invoked, is all associated state (such as carry) reset to the same -state that would have been created by the constructor -</p> -<blockquote><pre> -explicit <em>engine-type</em>(result_type s = default_seed) -</pre></blockquote> -<p> -or is the exact state unspecified? -<p/> -Implementations differ. -</p> - -<p><i>[2014-02-13, Issaquah]</i></p> - -<p> -Walter Brown says that Table 117 makes this very clear, and that the answer is "Yes" -<p/> -Suggested resolution: NAD -</p> - -<p><i>[2015-05-05 Lenexa: Move to NAD]</i></p> - - - -<p><b>Proposed resolution:</b></p> -<p> -Suggested resolution: NAD -</p> - - - - - -<hr> -<h3><a name="2355"></a>2355. <tt>"s"</tt> UDL suffix should be reserved for a compile-time string library type</h3> -<p><b>Section:</b> 21.7 [basic.string.literals] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Michael Price <b>Opened:</b> 2014-01-18 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The current draft uses the <tt>"s"</tt> UDL suffix as a UDL for <tt>basic_string<charT></tt> (21.7 [basic.string.literals]). -In light of EWG active issue <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3682.html#66">66</a> (concerning N3599), -the <tt>"s"</tt> suffix (when applied to character string literals) should be reserved for a compile-time string library type. -</p> - -<p><i>[Issaquah 2014-10-12: Move to NAD]</i></p> - - -<p>We discussed leaving the <tt>s</tt> UDL suffix for <tt>string_view</tt> in Portland, and voted strongly in favor of using it for <tt>std::string</tt>. -<tt>string</tt> is also an extremely widely used type, and the difference is observable in type deduction cases. -In addition, a compile-time string is likely to cost significant compile time, which we don't want to make the default with <tt>s</tt>.</p> -<table> - <caption>Mark 2355 as NAD?</caption> - <tr><td>SF</td><td>F</td><td>N</td><td>A</td><td>SA</td></tr> - <tr><td>8</td> <td>4</td><td>0</td><td>2</td><td>0</td></tr> -</table> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2373"></a>2373. Make new entities and names in namespace <tt>std</tt> conforming extensions</h3> -<p><b>Section:</b> 17.6.5 [conforming] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Chandler Carruth <b>Opened:</b> 2014-03-22 <b>Last modified:</b> 2015-05-22</p> -<p><b>View all other</b> <a href="lwg-index.html#conforming">issues</a> in [conforming].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -Technically, right now, it is not a conforming extension to add a new function to namespace <tt>std</tt>. Doing so could cause -unqualified lookup on the name of that function in the presence of a using directive to find a different function. This seems -an unreasonable restriction on library vendors providing conforming extensions, as such a using directive seems inherently risky -in unqualified name lookup. -</p> -<p> -17.6.5.5 [member.functions] implies that adding overloads to a method <em>is</em> a conforming extension, and within some -limits the same is true for global functions due to 17.6.5.4 [global.functions]. -<p/> -It would likely be useful to specify that other new entities are valid conforming extensions, or preclude them where they pose -serious compatibility problems. -</p> - -<p><i>[Lenexa 2015-05-06: Move to NAD]</i></p> - -<p>JY: It's a design question, move to LEWG?</p> -<p>AM: NAD: extensions led to us being unable to use the names hash_map, leading to unordered_map etc. Will result in collisions between members.</p> -<p>MC: Agrees, implementations that extend std:: must use __ugly_names for this reason.</p> -<p>JY: I would not oppose NAD.</p> -<p>Move to NAD, consensus.</p> - - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2382"></a>2382. Unclear order of container update versus object destruction on removing an object</h3> -<p><b>Section:</b> 17.6.5.8 [reentrancy] <b>Status:</b> <a href="lwg-active.html#NAD">Pending NAD</a> - <b>Submitter:</b> Peter Kasting <b>Opened:</b> 2014-05-06 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#reentrancy">issues</a> in [reentrancy].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#Pending NAD">Pending NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The standard does not seem to discuss reentrant access to a container during removal of an element, -leaving it unclear whether a removed object is destroyed before or after it is removed from the container. -For example, the behavior of the following code seems to be unspecified: -</p> -<blockquote><pre> -#include <iostream> -#include <map> -#include <memory> - -struct T; -typedef std::map<int, std::shared_ptr<T>> TMap; - -struct T { - T(TMap* t_map, int index) : t_map(t_map), index(index) {} - ~T() { - std::cout << "Object " << index << " is "; - if (t_map->count(index)) - std::cout << "destroyed before being removed from the map" << std::endl; - else - std::cout << "removed from the map before being destroyed" << std::endl; - } - - static void AddToMap(TMap* map, int index) { - (*map)[index] = std::make_shared<T>(map, index); - } - - TMap* t_map; - int index; -}; - -int main() -{ - TMap t_map; - T::AddToMap(&t_map, 0); - T::AddToMap(&t_map, 1); - t_map.erase(1); - t_map.erase(0); -} -</pre></blockquote> -<p> -The output of this program in Visual Studio 2013 is: -</p> -<blockquote><pre> -Object 1 is removed from the map before being destroyed -Object 0 is destroyed before being removed from the map -</pre></blockquote> -<p> -The core issue here is whether an object removed from a container should be destroyed before or after -it is removed from the container. The current standard seems to be silent on this issue. -The above output demonstrates that the behavior is actually inconsistent. (It's difficult to fully -describe Visual Studio's behavior; for example, changing <tt>main()</tt> in the above example to the following:) -</p> -<blockquote><pre> -int main() -{ - TMap t_map; - T::AddToMap(&t_map, 0); - T::AddToMap(&t_map, 1); - T::AddToMap(&t_map, 2); - T::AddToMap(&t_map, 3); - t_map.erase(3); - t_map.clear(); -} -</pre></blockquote> -<p> -(...gives this output:) -</p> -<blockquote><pre> -Object 3 is removed from the map before being destroyed -Object 2 is destroyed before being removed from the map -Object 1 is destroyed before being removed from the map -Object 0 is removed from the map before being destroyed -</pre></blockquote> -<p> -In my opinion, the standard should explicitly describe when objects are destroyed as part of removal from a container. -To me, it makes the most sense to say that objects should be removed from the container before they are destroyed. -</p> -<p><i>[2014-05-07, Jeffrey Yasskin comments]</i></p> - -<p> -I think there are two main points here beyond this writeup: -</p> -<ol> -<li><p>We can't make recursive use of a standard library container valid -in all cases.</p></li> -<li><p>If recursion through especially <tt>erase()</tt> is undefined behavior, -that's pretty scary for existing large applications with code in -destructors. Of course, "scary" doesn't mean we have to define the -behavior.</p></li> -</ol> -<p> -I'll add a third: The language in 17.6.5.8 [reentrancy] nearly makes this -undefined behavior already. I think any fix is probably going to live -there, and extend the current "implementation-defined" on recursive -reentrancy for individual functions to recursive reentrancy on class -instances. I'm not sure exactly how to word that. -</p> - -<p><i>[2014-06 Rapperswil]</i></p> - -<p> -STL: We need more wording about how container methods can be reentrency. -<p/> -Jeffrey: The title for this issue is confusing, what we really want is "reentrancy for objects". -<p/> -Alisdair: Should we then close 2382 as NAD with a link to the new issue? -</p> - - -<p><b>Proposed resolution:</b></p> - - - - - -<hr> -<h3><a name="2386"></a>2386. <tt>function::operator=</tt> handles allocators incorrectly</h3> -<p><b>Section:</b> 20.9.12.2.1 [func.wrap.func.con] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Pablo Halpern <b>Opened:</b> 2014-05-23 <b>Last modified:</b> 2015-05-05</p> -<p><b>View all other</b> <a href="lwg-index.html#func.wrap.func.con">issues</a> in [func.wrap.func.con].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -The <i>Effects</i> clauses for the assignment operator for class template <tt>function</tt> are -written as code that constructs a temporary <tt>function</tt> and then swaps it with <tt>*this</tt>. -The intention appears to be that assignment should have the strong exception -guarantee, i.e., <tt>*this</tt> is not modified if an exception is thrown. However, the current -description is incorrect when <tt>*this</tt> was constructed using an allocator. -<p/> -Part of the problem is the under-specification of <tt>swap</tt>, which does not state the -allocator requirements or allocator postconditions. If <tt>swap</tt> behaves like the rest of the -standard library, swapping function objects constructed with different allocators -would be undefined behavior. Alternatively <tt>swap</tt> could exchange the allocators, -though I would argue against this specification. -<p/> -For either specification of <tt>swap</tt>, the current <i>Effects</i> clauses for <tt>operator=</tt> are -incorrect. If <tt>swap</tt> does not exchange the allocators, then <tt>operator=</tt> would have -undefined behavior, which is clearly not desired. If <tt>swap</tt> does exchange the allocators, -then <tt>operator=</tt> would always leave the left-hand side (lhs) of the assignment with a -default allocator. The latter would be surprising behavior, as the allocator instance is -normally unchanged for the lifetime of an object (for good reason), and is certainly not -reset to default arbitrarily. -<p/> -The desired behavior is that assignment would leave the allocator of the lhs -unchanged. The way to achieve this behavior is to construct the temporary <tt>function</tt> -using the original allocator. Unfortunately, we cannot describe the desired behavior in -pure code, because there is no way to name the type-erased value of the allocator. -(N3916 would improve this situation for the Library Fundamentals TS, but even with -those changes, there is no way to recover the original type of the allocator.) The PR -below, therefore, uses pseudo-code, inventing a fictitious <tt><i>ALLOCATOR_OF</i>(f)</tt> -expression that evaluates to the actual allocator type, even if that allocator was type -erased. I have implemented this PR successfully. -</p> - -<p> -<strong>Previous resolution [SUPERSEDED]:</strong> -</p> -<blockquote class="note"> -<p>This wording is relative to N3936.</p> - -<ol> -<li><p>Change 20.9.12.2.1 [func.wrap.func.con] as indicated:</p> - -<blockquote> -<p> -<ins>In the following descriptions, <tt><i>ALLOCATOR_OF</i>(f)</tt> is a copy of the allocator specified in the -construction of <tt>function</tt> <tt>f</tt>, or <tt>allocator<char>()</tt> if no allocator was specified.</ins> -</p> -<pre> -function& operator=(const function& f); -</pre> -<blockquote> -<p> --12- <i>Effects</i>: <tt>function(<ins>allocator_arg, <i>ALLOCATOR_OF</i>(*this),</ins> f).swap(*this);</tt> -<p/> --13- <i>Returns</i>: <tt>*this</tt> -</p> -</blockquote> -<pre> -function& operator=(function&& f); -</pre> -<blockquote> -<p> --14- <i>Effects</i>: <del>Replaces the target of <tt>*this</tt> with the target of <tt>f</tt>.</del><ins><tt>function(allocator_arg, -<i>ALLOCATOR_OF</i>(*this), std::move(f)).swap(*this);</tt></ins> -<p/> --15- <i>Returns</i>: <tt>*this</tt> -</p> -</blockquote> -<pre> -function& operator=(nullptr_t); -</pre> -<blockquote> -<p> --16- <i>Effects</i>: If <tt>*this != nullptr</tt>, destroys the target of <tt>this</tt>. -<p/> --17- <i>Postconditions</i>: <tt>!(*this)</tt>. <ins>The allocator is unchanged.</ins> -<p/> --18- <i>Returns</i>: <tt>*this</tt> -<p/> -<ins>-?- <i>Throws</i>: Nothing.</ins> -</p> -</blockquote> -<pre> -template<class F> function& operator=(F&& f); -</pre> -<blockquote> -<p> --19- <i>Effects</i>: <tt>function(<ins>allocator_arg, <i>ALLOCATOR_OF</i>(*this),</ins> std::forward<F>(f)).swap(*this);</tt> -<p/> --20- <i>Returns</i>: <tt>*this</tt> -<p/> --21- <i>Remarks</i>: This assignment operator shall not participate in overload resolution unless -<tt>declval<typename decay<F>::type&>()</tt> is <tt>Callable</tt> (20.9.11.2) for argument types -<tt>ArgTypes...</tt> and return type <tt>R</tt>. -</p> -</blockquote> -<pre> -template<class F> function& operator=(reference_wrapper<F> f); -</pre> -<blockquote> -<p> --22- <i>Effects</i>: <tt>function(<ins>allocator_arg, <i>ALLOCATOR_OF</i>(*this),</ins> f).swap(*this);</tt> -<p/> --23- <i>Returns</i>: <tt>*this</tt> -</p> -</blockquote> - -</blockquote> -</li> - -</ol> - -</blockquote> - -<p><i>[2015-05, Lenexa]</i></p> - -<p> -STL: think this is NAD, don't think this is implementable or even should be.<br/> -STL: think this issue should be dealt with the same as 2370, don't think this should be done ever.<br/> -STL: NAD because there is nothing broken here.<br/> -STL: already fixed <tt>operator= noexcept</tt> so <i>Throws</i> nothing is not needed<br/> -STL: nothing to salvage here<br/> -MC: consensus for NAD -</p> - - -<p><b>Proposed resolution:</b></p> -<p> -There was consensus by the committee that the issue does not constitute as defect. -</p> - - - - - -<hr> -<h3><a name="2388"></a>2388. Handling self-assignment in the proposed library function <tt>std::exchange</tt></h3> -<p><b>Section:</b> 20.2.3 [utility.exchange] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Nick Calus <b>Opened:</b> 2014-05-09 <b>Last modified:</b> 2015-05-06</p> -<p><b>View all other</b> <a href="lwg-index.html#utility.exchange">issues</a> in [utility.exchange].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -In paper <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3668.html">N3668</a>, the addition of a template function -<tt>std::exchange</tt> had been proposed. In the rationale provided by the paper, we find the following: -</p> -<blockquote> -<p> -I chose the name for symmetry with <tt>atomic_exchange</tt>, since they behave the same except for this function not being atomic. -</p> -</blockquote> -<p> -and: -</p> -<blockquote> -<p> -Atomic objects provide an <tt>atomic_exchange</tt> function ([atomics.types.operations.req]p18) that <em>assigns a new value to the object -and returns the old value</em>. This operation is also useful on non-atomic objects, and this paper proposes adding it to the library. -<p/> -But the specified semantics of <tt>std::exchange</tt> is defined as follows: -</p> -</blockquote> -<blockquote><pre> -template <class T, class U=T> T exchange(T& obj, U&& new_val); -</pre> -<blockquote> -<p> -<i>Effects</i>: Equivalent to: -</p> -<blockquote><pre> -T old_val = std::move(obj); -obj = std::forward<U>(new_val); -return old_val; -</pre> -</blockquote> -</blockquote> -</blockquote> -<p> -When looking at the post-condition of the <tt>std::exchange</tt> function, one would expect the return value to be the old value -of <tt>obj</tt> and also that <tt>obj</tt> now contains the value of <tt>new_value</tt>. -This post-condition is violated when <tt>obj</tt> is a reference to the same object as <tt>new_value</tt> and type <tt>T</tt> -has move semantics. -<p/> -Given it's specification, it is clear that <tt>std::exchange</tt> is meant to be used with types that have move semantics. -Therefore, the post-condition is violated for self-assignments. -<p/> -Suppose the following situation: -<p/> -You have a vector of objects. The objects implement move semantics and are emptied when moved from. -You provide a function that allows you to replace an object at a specific index by a new object (provided by reference as -an argument to your function). When replacing an object, your function calls a member-function <tt>do_something_fancy</tt> -on the old object. -</p> -<blockquote><pre> -void your_function(int i, X& new_val) { - std::exchange(vec[i], new_val).do_something_fancy(); -} -</pre></blockquote> -<p> -Your function gets called with a given index and the corresponding element of said vector. (by coincidence or by purpose, it -doesn't really matter) -</p> -<blockquote><pre> -your_function(5, vec[5]); -</pre></blockquote> -<p> -This will cause the object at <tt>vec[5]</tt> to be in an empty state. -If this object would not implement move semantics, assignment performance is potentially worse, but at least it -is not in an empty (to my business logic, invalid) state. -<p/> -So to me, the current reference implementation of <tt>std::exchange</tt> does not have the behavior it is expected to have. -</p> - -<p><i>[2014-12-18 Telecon]</i></p> - -<p> -MC: does this resolution solve the problem? -<p/> -JW: and is the cost of the extra construction and move acceptable? -<p/> -AM: not all moves are cheap -<p/> -VV: seems like a design change -<p/> -JW: maybe this should be rolled into my unwritten paper on self-swap, so we deal with them consistently -<p/> -VV: we should update the issue saying something like that and maybe NAD Future -<p/> -MC: instead, add Requires clause saying the arguments are not the same. -<p/> -JW: interesting, that can even be checked in a debug mode assertion -<p/> -MC: ACTION: send alternative P/R that we can consider -</p> - -<p> -<strong>Previous resolution [SUPERSEDED]:</strong> -</p> -<blockquote class="note"> -<p>This wording is relative to N3936.</p> - -<ol> -<li><p>Change 20.2.3 [utility.exchange] as indicated:</p> -<blockquote><pre> -template <class T, class U=T> T exchange(T& obj, U&& new_val); -</pre> -<blockquote> -<p> --1- <i>Effects</i>: Equivalent to: -</p> -<blockquote><pre> -<ins>T tmp = std::forward<U>(new_val);</ins> -T old_val = std::move(obj); -obj = <del>std::forward<U>(new_val)</del><ins>std::move(tmp)</ins>; -return old_val; -</pre> -</blockquote> -</blockquote> -</blockquote> -</li> -</ol> -</blockquote> - -<p> -<strong>Previous resolution from Marshall [SUPERSEDED]:</strong> -</p> -<blockquote class="note"> -<p>This wording is relative to N4296.</p> - -<ol> -<li><p>Change 20.2.3 [utility.exchange] as indicated:</p> -<blockquote><pre> -template <class T, class U=T> T exchange(T& obj, U&& new_val); -</pre> -<blockquote> -<p> -<ins>-?- <i>Requires</i>: <tt>obj</tt> and <tt>new_val</tt> shall not refer to the same object.</ins> -<p/> --1- <i>Effects</i>: Equivalent to: -</p> -<blockquote><pre> -T old_val = std::move(obj); -obj = std::forward<U>(new_val); -return old_val; -</pre> -</blockquote> -</blockquote> -</blockquote> -</li> -</ol> -</blockquote> - -<p><i>[2015-03-30, Marshall provides alternative wording]</i></p> - - -<p><i>[2015-05, Lenexa]</i></p> - -<p> -MC: self <tt>exchange</tt> does not work<br/> -MC: PR is just to add requires<br/> -STL: what if the new thing is a subobject, isn't that just as bad, any aliasing<br/> -STL: don't know that we need to do anything here if we aren't changing the implementation<br/> -NM: should remove the requires<br/> -MC: so NAD<br/> -STL: could add note<br/> -NM: remove requires<br/> -DK: requires isn't already there<br/> -RL: no note?<br/> -STL: no note, NAD, burden for next person that asks about aliasing<br/> -DK: what do we do for <tt>swap</tt>?<br/> -STL: self <tt>swap</tt> has always been noop, <tt>exchange</tt> could do something bad because it clears out<br/> -MC: alright, NAD it is<br/> -</p> - - - -<p><b>Proposed resolution:</b></p> -The current specification is clear about the implications described by the issue example and is as intended. - - - - - -<hr> -<h3><a name="2405"></a>2405. <tt>rotate()</tt>'s return value is incorrect when <tt>middle == first</tt></h3> -<p><b>Section:</b> 25.3.11 [alg.rotate] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2014-06-14 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#alg.rotate">issues</a> in [alg.rotate].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -When LWG <a href="lwg-defects.html#488">488</a> was resolved, the intention was to return "where the subrange <tt>[first, middle)</tt> starts after -the rotate is performed". However, this wasn't achieved in one case. -<p/> -When <tt>middle == last</tt>, <tt>rotate()</tt> does nothing and returns <tt>first</tt>. This is good. -<p/> -When <tt>middle == first</tt>, <tt>rotate()</tt> does nothing and returns <tt>last</tt>. This is bad. In addition to being -inconsistent with the other do-nothing case, it prevents <tt>rotate()</tt> from providing the useful guarantee that LWG -<a href="lwg-defects.html#488">488</a> wanted: when <tt>[first, last)</tt> is non-empty, <tt>rotate()</tt>'s return value should always be -dereferenceable to get the originally-first element. -<p/> -Howard Hinnant: -<p/> -As the author of LWG <a href="lwg-defects.html#488">488</a> I can assure everyone that the edge cases the proposed resolution specifies were -not specified by accident. <tt>rotate(i, i, j)</tt> should return <tt>j</tt> and <tt>rotate(i, j, j)</tt> should return <tt>i</tt>. -Doing otherwise will break working code. These return values were motivated by the uses of <tt>rotate</tt> in the implementation -of algorithms such as <tt>stable_partition</tt> and <tt>inplace_merge</tt>. The results of these edge cases were not chosen lightly. -<p/> -Also a good read: -<p/> -<a href="http://www.cs.rpi.edu/~musser/gsd/notes-on-programming-2006-10-13.pdf">notes-on-programming-2006-10-13</a> -<p/> -Summary: NAD. -</p> - -<p><i>[2014-06-16 Rapperswill]</i></p> - -<p> -Closed as NAD. -</p> - - - - -<p><b>Proposed resolution:</b></p> -<p>This wording is relative to N3936.</p> - -<ol> -<li><p>Change 25.3.11 [alg.rotate] p2 as indicated:</p> - -<blockquote> -<p> --2- <i>Returns</i>: <ins>If <tt>middle == first</tt>, returns <tt>first</tt>. Otherwise, returns</ins> <tt>first + (last - middle)</tt>. -</p> -</blockquote> -</li> - -</ol> - - - - - -<hr> -<h3><a name="2429"></a>2429. <tt>std::basic_ostringstream</tt> is missing an allocator-extended constructor</h3> -<p><b>Section:</b> 27.8.4 [ostringstream] <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a> - <b>Submitter:</b> Markus Kemp <b>Opened:</b> 2014-09-03 <b>Last modified:</b> 2015-04-08</p> -<p><b>View all other</b> <a href="lwg-index.html#ostringstream">issues</a> in [ostringstream].</p> -<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p> -<p><b>Discussion:</b></p> -<p> -I initially brought this issue up on <a href="http://stackoverflow.com/questions/23955828/how-to-use-basic-ostringstream-with-stateful-custom-allocator-c11">Stack Overflow</a>, -where I was then told to make a topic about this problem on <a href="https://groups.google.com/a/isocpp.org/d/msg/std-discussion/kAQFOWz47m0/cOXSHa5Iwg4J">std-discussion</a>, -where I was then in turn asked to report the issue. -<p/> -The problem: The <tt>std::basic_ostringstream</tt> class template can be instantiated with an allocator type, but none of the -constructors provided accept an allocator argument, which means it's impossible to use <tt>std::basic_ostringstream</tt> with -stateful allocators. The C++ Standard Library Defect Report List seems to already mention a similar issue (<a href="lwg-defects.html#2210">2210</a>). -</p> - - -<p><i>[2014-11 Urbana]</i></p> - -<p>Closed as NAD</p> -<p> -This is not a rejection of the suggestion, but an observation that simply adding an allocator-aware -constructor is only part of the problem. <tt>stringstream</tt> returns the <tt>string</tt> assembled -in its buffer by value, as the result of a call to <tt>str</tt>, and typically this will not use the -same allocator as would be supplied at construction. -</p> -<p> -The appropriate way to make progress on this issue, if motivated, is to submit a paper to LEWG -addressing the larger design concerns in addition to 'just' adding an (optional) allocator to -the constructors. -</p> - -<p><b>Proposed resolution:</b></p> - - - - - -</body> -</html> |