summaryrefslogtreecommitdiff
path: root/Doc/Manual/Typemaps.html
blob: cba524149f28dc416d8d2de8b956aad9357ec5ff (plain) 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
2304
2305
2306
2307
2308
2309
2310
2311
2312
2313
2314
2315
2316
2317
2318
2319
2320
2321
2322
2323
2324
2325
2326
2327
2328
2329
2330
2331
2332
2333
2334
2335
2336
2337
2338
2339
2340
2341
2342
2343
2344
2345
2346
2347
2348
2349
2350
2351
2352
2353
2354
2355
2356
2357
2358
2359
2360
2361
2362
2363
2364
2365
2366
2367
2368
2369
2370
2371
2372
2373
2374
2375
2376
2377
2378
2379
2380
2381
2382
2383
2384
2385
2386
2387
2388
2389
2390
2391
2392
2393
2394
2395
2396
2397
2398
2399
2400
2401
2402
2403
2404
2405
2406
2407
2408
2409
2410
2411
2412
2413
2414
2415
2416
2417
2418
2419
2420
2421
2422
2423
2424
2425
2426
2427
2428
2429
2430
2431
2432
2433
2434
2435
2436
2437
2438
2439
2440
2441
2442
2443
2444
2445
2446
2447
2448
2449
2450
2451
2452
2453
2454
2455
2456
2457
2458
2459
2460
2461
2462
2463
2464
2465
2466
2467
2468
2469
2470
2471
2472
2473
2474
2475
2476
2477
2478
2479
2480
2481
2482
2483
2484
2485
2486
2487
2488
2489
2490
2491
2492
2493
2494
2495
2496
2497
2498
2499
2500
2501
2502
2503
2504
2505
2506
2507
2508
2509
2510
2511
2512
2513
2514
2515
2516
2517
2518
2519
2520
2521
2522
2523
2524
2525
2526
2527
2528
2529
2530
2531
2532
2533
2534
2535
2536
2537
2538
2539
2540
2541
2542
2543
2544
2545
2546
2547
2548
2549
2550
2551
2552
2553
2554
2555
2556
2557
2558
2559
2560
2561
2562
2563
2564
2565
2566
2567
2568
2569
2570
2571
2572
2573
2574
2575
2576
2577
2578
2579
2580
2581
2582
2583
2584
2585
2586
2587
2588
2589
2590
2591
2592
2593
2594
2595
2596
2597
2598
2599
2600
2601
2602
2603
2604
2605
2606
2607
2608
2609
2610
2611
2612
2613
2614
2615
2616
2617
2618
2619
2620
2621
2622
2623
2624
2625
2626
2627
2628
2629
2630
2631
2632
2633
2634
2635
2636
2637
2638
2639
2640
2641
2642
2643
2644
2645
2646
2647
2648
2649
2650
2651
2652
2653
2654
2655
2656
2657
2658
2659
2660
2661
2662
2663
2664
2665
2666
2667
2668
2669
2670
2671
2672
2673
2674
2675
2676
2677
2678
2679
2680
2681
2682
2683
2684
2685
2686
2687
2688
2689
2690
2691
2692
2693
2694
2695
2696
2697
2698
2699
2700
2701
2702
2703
2704
2705
2706
2707
2708
2709
2710
2711
2712
2713
2714
2715
2716
2717
2718
2719
2720
2721
2722
2723
2724
2725
2726
2727
2728
2729
2730
2731
2732
2733
2734
2735
2736
2737
2738
2739
2740
2741
2742
2743
2744
2745
2746
2747
2748
2749
2750
2751
2752
2753
2754
2755
2756
2757
2758
2759
2760
2761
2762
2763
2764
2765
2766
2767
2768
2769
2770
2771
2772
2773
2774
2775
2776
2777
2778
2779
2780
2781
2782
2783
2784
2785
2786
2787
2788
2789
2790
2791
2792
2793
2794
2795
2796
2797
2798
2799
2800
2801
2802
2803
2804
2805
2806
2807
2808
2809
2810
2811
2812
2813
2814
2815
2816
2817
2818
2819
2820
2821
2822
2823
2824
2825
2826
2827
2828
2829
2830
2831
2832
2833
2834
2835
2836
2837
2838
2839
2840
2841
2842
2843
2844
2845
2846
2847
2848
2849
2850
2851
2852
2853
2854
2855
2856
2857
2858
2859
2860
2861
2862
2863
2864
2865
2866
2867
2868
2869
2870
2871
2872
2873
2874
2875
2876
2877
2878
2879
2880
2881
2882
2883
2884
2885
2886
2887
2888
2889
2890
2891
2892
2893
2894
2895
2896
2897
2898
2899
2900
2901
2902
2903
2904
2905
2906
2907
2908
2909
2910
2911
2912
2913
2914
2915
2916
2917
2918
2919
2920
2921
2922
2923
2924
2925
2926
2927
2928
2929
2930
2931
2932
2933
2934
2935
2936
2937
2938
2939
2940
2941
2942
2943
2944
2945
2946
2947
2948
2949
2950
2951
2952
2953
2954
2955
2956
2957
2958
2959
2960
2961
2962
2963
2964
2965
2966
2967
2968
2969
2970
2971
2972
2973
2974
2975
2976
2977
2978
2979
2980
2981
2982
2983
2984
2985
2986
2987
2988
2989
2990
2991
2992
2993
2994
2995
2996
2997
2998
2999
3000
3001
3002
3003
3004
3005
3006
3007
3008
3009
3010
3011
3012
3013
3014
3015
3016
3017
3018
3019
3020
3021
3022
3023
3024
3025
3026
3027
3028
3029
3030
3031
3032
3033
3034
3035
3036
3037
3038
3039
3040
3041
3042
3043
3044
3045
3046
3047
3048
3049
3050
3051
3052
3053
3054
3055
3056
3057
3058
3059
3060
3061
3062
3063
3064
3065
3066
3067
3068
3069
3070
3071
3072
3073
3074
3075
3076
3077
3078
3079
3080
3081
3082
3083
3084
3085
3086
3087
3088
3089
3090
3091
3092
3093
3094
3095
3096
3097
3098
3099
3100
3101
3102
3103
3104
3105
3106
3107
3108
3109
3110
3111
3112
3113
3114
3115
3116
3117
3118
3119
3120
3121
3122
3123
3124
3125
3126
3127
3128
3129
3130
3131
3132
3133
3134
3135
3136
3137
3138
3139
3140
3141
3142
3143
3144
3145
3146
3147
3148
3149
3150
3151
3152
3153
3154
3155
3156
3157
3158
3159
3160
3161
3162
3163
3164
3165
3166
3167
3168
3169
3170
3171
3172
3173
3174
3175
3176
3177
3178
3179
3180
3181
3182
3183
3184
3185
3186
3187
3188
3189
3190
3191
3192
3193
3194
3195
3196
3197
3198
3199
3200
3201
3202
3203
3204
3205
3206
3207
3208
3209
3210
3211
3212
3213
3214
3215
3216
3217
3218
3219
3220
3221
3222
3223
3224
3225
3226
3227
3228
3229
3230
3231
3232
3233
3234
3235
3236
3237
3238
3239
3240
3241
3242
3243
3244
3245
3246
3247
3248
3249
3250
3251
3252
3253
3254
3255
3256
3257
3258
3259
3260
3261
3262
3263
3264
3265
3266
3267
3268
3269
3270
3271
3272
3273
3274
3275
3276
3277
3278
3279
3280
3281
3282
3283
3284
3285
3286
3287
3288
3289
3290
3291
3292
3293
3294
3295
3296
3297
3298
3299
3300
3301
3302
3303
3304
3305
3306
3307
3308
3309
3310
3311
3312
3313
3314
3315
3316
3317
3318
3319
3320
3321
3322
3323
3324
3325
3326
3327
3328
3329
3330
3331
3332
3333
3334
3335
3336
3337
3338
3339
3340
3341
3342
3343
3344
3345
3346
3347
3348
3349
3350
3351
3352
3353
3354
3355
3356
3357
3358
3359
3360
3361
3362
3363
3364
3365
3366
3367
3368
3369
3370
3371
3372
3373
3374
3375
3376
3377
3378
3379
3380
3381
3382
3383
3384
3385
3386
3387
3388
3389
3390
3391
3392
3393
3394
3395
3396
3397
3398
3399
3400
3401
3402
3403
3404
3405
3406
3407
3408
3409
3410
3411
3412
3413
3414
3415
3416
3417
3418
3419
3420
3421
3422
3423
3424
3425
3426
3427
3428
3429
3430
3431
3432
3433
3434
3435
3436
3437
3438
3439
3440
3441
3442
3443
3444
3445
3446
3447
3448
3449
3450
3451
3452
3453
3454
3455
3456
3457
3458
3459
3460
3461
3462
3463
3464
3465
3466
3467
3468
3469
3470
3471
3472
3473
3474
3475
3476
3477
3478
3479
3480
3481
3482
3483
3484
3485
3486
3487
3488
3489
3490
3491
3492
3493
3494
3495
3496
3497
3498
3499
3500
3501
3502
3503
3504
3505
3506
3507
3508
3509
3510
3511
3512
3513
3514
3515
3516
3517
3518
3519
3520
3521
3522
3523
3524
3525
3526
3527
3528
3529
3530
3531
3532
3533
3534
3535
3536
3537
3538
3539
3540
3541
3542
3543
3544
3545
3546
3547
3548
3549
3550
3551
3552
3553
3554
3555
3556
3557
3558
3559
3560
3561
3562
3563
3564
3565
3566
3567
3568
3569
3570
3571
3572
3573
3574
3575
3576
3577
3578
3579
3580
3581
3582
3583
3584
3585
3586
3587
3588
3589
3590
3591
3592
3593
3594
3595
3596
3597
3598
3599
3600
3601
3602
3603
3604
3605
3606
3607
3608
3609
3610
3611
3612
3613
3614
3615
3616
3617
3618
3619
3620
3621
3622
3623
3624
3625
3626
3627
3628
3629
3630
3631
3632
3633
3634
3635
3636
3637
3638
3639
3640
3641
3642
3643
3644
3645
3646
3647
3648
3649
3650
3651
3652
3653
3654
3655
3656
3657
3658
3659
3660
3661
3662
3663
3664
3665
3666
3667
3668
3669
3670
3671
3672
3673
3674
3675
3676
3677
3678
3679
3680
3681
3682
3683
3684
3685
3686
3687
3688
3689
3690
3691
3692
3693
3694
3695
3696
3697
3698
3699
3700
3701
3702
3703
3704
3705
3706
3707
3708
3709
3710
3711
3712
3713
3714
3715
3716
3717
3718
3719
3720
3721
3722
3723
3724
3725
3726
3727
3728
3729
3730
3731
3732
3733
3734
3735
3736
3737
3738
3739
3740
3741
3742
3743
3744
3745
3746
3747
3748
3749
3750
3751
3752
3753
3754
3755
3756
3757
3758
3759
3760
3761
3762
3763
3764
3765
3766
3767
3768
3769
3770
3771
3772
3773
3774
3775
3776
3777
3778
3779
3780
3781
3782
3783
3784
3785
3786
3787
3788
3789
3790
3791
3792
3793
3794
3795
3796
3797
3798
3799
3800
3801
3802
3803
3804
3805
3806
3807
3808
3809
3810
3811
3812
3813
3814
3815
3816
3817
3818
3819
3820
3821
3822
3823
3824
3825
3826
3827
3828
3829
3830
3831
3832
3833
3834
3835
3836
3837
3838
3839
3840
3841
3842
3843
3844
3845
3846
3847
3848
3849
3850
3851
3852
3853
3854
3855
3856
3857
3858
3859
3860
3861
3862
3863
3864
3865
3866
3867
3868
3869
3870
3871
3872
3873
3874
3875
3876
3877
3878
3879
3880
3881
3882
3883
3884
3885
3886
3887
3888
3889
3890
3891
3892
3893
3894
3895
3896
3897
3898
3899
3900
3901
3902
3903
3904
3905
3906
3907
3908
3909
3910
3911
3912
3913
3914
3915
3916
3917
3918
3919
3920
3921
3922
3923
3924
3925
3926
3927
3928
3929
3930
3931
3932
3933
3934
3935
3936
3937
3938
3939
3940
3941
3942
3943
3944
3945
3946
3947
3948
3949
3950
3951
3952
3953
3954
3955
3956
3957
3958
3959
3960
3961
3962
3963
3964
3965
3966
3967
3968
3969
3970
3971
3972
3973
3974
3975
3976
3977
3978
3979
3980
3981
3982
3983
3984
3985
3986
3987
3988
3989
3990
3991
3992
3993
3994
3995
3996
3997
3998
3999
4000
4001
4002
4003
4004
4005
4006
4007
4008
4009
4010
4011
4012
4013
4014
4015
4016
4017
4018
4019
4020
4021
4022
4023
4024
4025
4026
4027
4028
4029
4030
4031
4032
4033
4034
4035
4036
4037
4038
4039
4040
4041
4042
4043
4044
4045
4046
4047
4048
4049
4050
4051
4052
4053
4054
4055
4056
4057
4058
4059
4060
4061
4062
4063
4064
4065
4066
4067
4068
4069
4070
4071
4072
4073
4074
4075
4076
4077
4078
4079
4080
4081
4082
4083
4084
4085
4086
4087
4088
4089
4090
4091
4092
4093
4094
4095
4096
4097
4098
4099
4100
4101
4102
4103
4104
4105
4106
4107
4108
4109
4110
4111
4112
4113
4114
4115
4116
4117
4118
4119
4120
4121
4122
4123
4124
4125
4126
4127
4128
4129
4130
4131
4132
4133
4134
4135
4136
4137
4138
4139
4140
4141
4142
4143
4144
4145
4146
4147
4148
4149
4150
4151
4152
4153
4154
4155
4156
4157
4158
4159
4160
4161
4162
4163
4164
4165
4166
4167
4168
4169
4170
4171
4172
4173
4174
4175
4176
4177
4178
4179
4180
4181
4182
4183
4184
4185
4186
4187
4188
4189
4190
4191
4192
4193
4194
4195
4196
4197
4198
4199
4200
4201
4202
4203
4204
4205
4206
4207
4208
4209
4210
4211
4212
4213
4214
4215
4216
4217
4218
4219
4220
4221
4222
4223
4224
4225
4226
4227
4228
4229
4230
4231
4232
4233
4234
4235
4236
4237
4238
4239
4240
4241
4242
4243
4244
4245
4246
4247
4248
4249
4250
4251
4252
4253
4254
4255
4256
4257
4258
4259
4260
4261
4262
4263
4264
4265
4266
4267
4268
4269
4270
4271
4272
4273
4274
4275
4276
4277
4278
4279
4280
4281
4282
4283
4284
4285
4286
4287
4288
4289
4290
4291
4292
4293
4294
4295
4296
4297
4298
4299
4300
4301
4302
4303
4304
4305
4306
4307
4308
4309
4310
4311
4312
4313
4314
4315
4316
4317
4318
4319
4320
4321
4322
4323
4324
4325
4326
4327
4328
4329
4330
4331
4332
4333
4334
4335
4336
4337
4338
4339
4340
4341
4342
4343
4344
4345
4346
4347
4348
4349
4350
4351
4352
4353
4354
4355
4356
4357
4358
4359
4360
4361
4362
4363
4364
4365
4366
4367
4368
4369
4370
4371
4372
4373
4374
4375
4376
4377
4378
4379
4380
4381
4382
4383
4384
4385
4386
4387
4388
4389
4390
4391
4392
4393
4394
4395
4396
4397
4398
4399
4400
4401
4402
4403
4404
4405
4406
4407
4408
4409
4410
4411
4412
4413
4414
4415
4416
4417
4418
4419
4420
4421
4422
4423
4424
4425
4426
4427
4428
4429
4430
4431
4432
4433
4434
4435
4436
4437
4438
4439
4440
4441
4442
4443
4444
4445
4446
4447
4448
4449
4450
4451
4452
4453
4454
4455
4456
4457
4458
4459
4460
4461
4462
4463
4464
4465
4466
4467
4468
4469
4470
4471
4472
4473
4474
4475
4476
4477
4478
4479
4480
4481
4482
4483
4484
4485
4486
4487
4488
4489
4490
4491
4492
4493
4494
4495
4496
4497
4498
4499
4500
4501
4502
4503
4504
4505
4506
4507
4508
4509
4510
4511
4512
4513
4514
4515
4516
4517
4518
4519
4520
4521
4522
4523
4524
4525
4526
4527
4528
4529
4530
4531
4532
4533
4534
4535
4536
4537
4538
4539
4540
4541
4542
4543
4544
4545
4546
4547
4548
4549
4550
4551
4552
4553
4554
4555
4556
4557
4558
4559
4560
4561
4562
4563
4564
4565
4566
4567
4568
4569
4570
4571
4572
4573
4574
4575
4576
4577
4578
4579
4580
4581
4582
4583
4584
4585
4586
4587
4588
4589
4590
4591
4592
4593
4594
4595
4596
4597
4598
4599
4600
4601
4602
4603
4604
4605
4606
4607
4608
4609
4610
4611
4612
4613
4614
4615
4616
4617
4618
4619
4620
4621
4622
4623
4624
4625
4626
4627
4628
4629
4630
4631
4632
4633
4634
4635
4636
4637
4638
4639
4640
4641
4642
4643
4644
4645
4646
4647
4648
4649
4650
4651
4652
4653
4654
4655
4656
4657
4658
4659
4660
4661
4662
4663
4664
4665
4666
4667
4668
4669
4670
4671
4672
4673
4674
4675
4676
4677
4678
4679
4680
4681
4682
4683
4684
4685
4686
4687
4688
4689
4690
4691
4692
4693
4694
4695
4696
4697
4698
4699
4700
4701
4702
4703
4704
4705
4706
4707
4708
4709
4710
4711
4712
4713
4714
4715
4716
4717
4718
4719
4720
4721
4722
4723
4724
4725
4726
4727
4728
4729
4730
4731
4732
4733
4734
4735
4736
4737
4738
4739
4740
4741
4742
4743
4744
4745
4746
4747
4748
4749
4750
4751
4752
4753
4754
4755
4756
4757
4758
4759
4760

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<title>Typemaps</title>
<link rel="stylesheet" type="text/css" href="style.css">
</head>

<body bgcolor="#ffffff">
<H1><a name="Typemaps"></a>11 Typemaps</H1>
<!-- INDEX -->
<div class="sectiontoc">
<ul>
<li><a href="#Typemaps_nn2">Introduction</a>
<ul>
<li><a href="#Typemaps_nn3">Type conversion</a>
<li><a href="#Typemaps_nn4">Typemaps</a>
<li><a href="#Typemaps_nn5">Pattern matching</a>
<li><a href="#Typemaps_nn6">Reusing typemaps</a>
<li><a href="#Typemaps_nn7">What can be done with typemaps?</a>
<li><a href="#Typemaps_nn8">What can't be done with typemaps?</a>
<li><a href="#Typemaps_aspects">Similarities to Aspect Oriented Programming</a>
<li><a href="#Typemaps_nn9">The rest of this chapter</a>
</ul>
<li><a href="#Typemaps_nn10">Typemap specifications</a>
<ul>
<li><a href="#Typemaps_defining">Defining a typemap</a>
<li><a href="#Typemaps_nn12">Typemap scope</a>
<li><a href="#Typemaps_nn13">Copying a typemap</a>
<li><a href="#Typemaps_nn14">Deleting a typemap</a>
<li><a href="#Typemaps_nn15">Placement of typemaps</a>
</ul>
<li><a href="#Typemaps_pattern_matching">Pattern matching rules</a>
<ul>
<li><a href="#Typemaps_nn17">Basic matching rules</a>
<li><a href="#Typemaps_typedef_reductions">Typedef reductions matching</a>
<li><a href="#Typemaps_nn19">Default typemap matching rules</a>
<li><a href="#Typemaps_multi_argument_typemaps_patterns">Multi-arguments typemaps</a>
<li><a href="#Typemaps_matching_template_comparison">Matching rules compared to C++ templates</a>
<li><a href="#Typemaps_debugging_search">Debugging typemap pattern matching</a>
</ul>
<li><a href="#Typemaps_nn21">Code generation rules</a>
<ul>
<li><a href="#Typemaps_nn22">Scope</a>
<li><a href="#Typemaps_nn23">Declaring new local variables</a>
<li><a href="#Typemaps_special_variables">Special variables</a>
<li><a href="#Typemaps_special_variable_macros">Special variable macros</a>
<ul>
<li><a href="#Typemaps_special_macro_descriptor">$descriptor(type)</a>
<li><a href="#Typemaps_special_macro_typemap">$typemap(method, typepattern)</a>
</ul>
</ul>
<li><a href="#Typemaps_nn25">Common typemap methods</a>
<ul>
<li><a href="#Typemaps_nn26">"in" typemap</a>
<li><a href="#Typemaps_nn27">"typecheck" typemap</a>
<li><a href="#Typemaps_nn28">"out" typemap</a>
<li><a href="#Typemaps_nn29">"arginit" typemap</a>
<li><a href="#Typemaps_nn30">"default" typemap</a>
<li><a href="#Typemaps_nn31">"check" typemap</a>
<li><a href="#Typemaps_nn32">"argout" typemap</a>
<li><a href="#Typemaps_nn33">"freearg" typemap</a>
<li><a href="#Typemaps_nn34">"newfree" typemap</a>
<li><a href="#Typemaps_nn35">"memberin" typemap</a>
<li><a href="#Typemaps_nn36">"varin" typemap</a>
<li><a href="#Typemaps_nn37">"varout" typemap</a>
<li><a href="#throws_typemap">"throws" typemap</a>
</ul>
<li><a href="#Typemaps_nn39">Some typemap examples</a>
<ul>
<li><a href="#Typemaps_nn40">Typemaps for arrays</a>
<li><a href="#Typemaps_nn41">Implementing constraints with typemaps</a>
</ul>
<li><a href="#Typemaps_nn43">Typemaps for multiple target languages</a>
<li><a href="#Typemaps_optimal">Optimal code generation when returning by value</a>
<li><a href="#Typemaps_multi_argument_typemaps">Multi-argument typemaps</a>
<li><a href="#Typemaps_warnings">Typemap warnings</a>
<li><a href="#Typemaps_fragments">Typemap fragments</a>
<ul>
<li><a href="#Typemaps_fragment_type_specialization">Fragment type specialization</a>
<li><a href="#Typemaps_automatic_specialization">Fragments and automatic typemap specialization</a>
</ul>
<li><a href="#Typemaps_runtime_type_checker">The run-time type checker</a>
<ul>
<li><a href="#Typemaps_nn45">Implementation</a>
<li><a href="#Typemaps_runtime_type_checker_usage">Usage</a>
</ul>
<li><a href="#Typemaps_overloading">Typemaps and overloading</a>
<li><a href="#Typemaps_nn48">More about <tt>%apply</tt> and <tt>%clear</tt></a>
<li><a href="#Typemaps_nn47">Passing data between typemaps</a>
<li><a href="#Typemaps_nn52">C++ "this" pointer</a>
<li><a href="#Typemaps_nn51">Where to go for more information?</a>
</ul>
</div>
<!-- INDEX -->



<H2><a name="Typemaps_nn2"></a>11.1 Introduction</H2>


<p>
Chances are, you are reading this chapter for one of two reasons; you
either want to customize SWIG's behavior or you overheard someone
mumbling some incomprehensible drivel about "typemaps" and you asked
yourself "typemaps, what are those?"  That said, let's start with a
short disclaimer that "typemaps" are an advanced customization feature
that provide direct access to SWIG's low-level code generator. Not
only that, they are an integral part of the SWIG C++ type system (a
non-trivial topic of its own).  Typemaps are generally
<em>not</em> a required part of using SWIG.  Therefore, you might want
to re-read the earlier chapters if you have found your way to this
chapter with only a vague idea of what SWIG already does by default.
</p>

<H3><a name="Typemaps_nn3"></a>11.1.1 Type conversion</H3>


<p>
One of the most important problems in wrapper code generation is the
conversion or marshalling of datatypes between programming languages.  Specifically,
for every C/C++ declaration, SWIG must somehow generate wrapper code
that allows values to be passed back and forth between languages.
Since every programming language represents data differently, this is
not a simple of matter of simply linking code together with the
C linker.  Instead, SWIG has to know something about how data is
represented in each language and how it can be manipulated.
</p>

<p>
To illustrate, suppose you had a simple C function like this:
</p>

<div class="code">
<pre>
int factorial(int n);
</pre>
</div>

<p>
To access this function from Python, a pair of Python API functions
are used to convert integer values.  For example:
</p>

<div class="code">
<pre>
long PyInt_AsLong(PyObject *obj);      /* Python --&gt; C */
PyObject *PyInt_FromLong(long x);      /* C --&gt; Python */
</pre>
</div>

<p>
The first function is used to convert the input argument from a Python integer object
to C <tt>long</tt>.  The second function is used to convert a value from C back into a Python integer object. 
</p>

<p>
Inside the wrapper function, you might see these functions used like this:
</p>

<div class="code">
<pre>
PyObject *wrap_factorial(PyObject *self, PyObject *args) {
    int       arg1;
    int       result;
    PyObject *obj1;
    PyObject *resultobj;

    if (!PyArg_ParseTuple("O:factorial", &amp;obj1)) return NULL;
    <b>arg1 = PyInt_AsLong(obj1);</b>
    result = factorial(arg1);
    <b>resultobj = PyInt_FromLong(result);</b>
    return resultobj;
}
</pre>
</div>

<p>
Every target language supported by SWIG has functions that work in a similar manner.  For example, in
Perl, the following functions are used:
</p>

<div class="code">
<pre>
IV SvIV(SV *sv);                     /* Perl --&gt; C */
void sv_setiv(SV *sv, IV val);       /* C --&gt; Perl */
</pre>
</div>

<p>
In Tcl:
</p>

<div class="code">
<pre>
int Tcl_GetLongFromObj(Tcl_Interp *interp, Tcl_Obj *obj, long *value);
Tcl_Obj *Tcl_NewIntObj(long value);
</pre>
</div>

<p>
The precise details are not so important.  What is important is that
all of the underlying type conversion is handled by collections of
utility functions and short bits of C code like this---you simply have
to read the extension documentation for your favorite language to know
how it works (an exercise left to the reader).
</p>

<H3><a name="Typemaps_nn4"></a>11.1.2 Typemaps</H3>


<p>
Since type handling is so central to wrapper code generation, SWIG
allows it to be completely defined (or redefined) by the user.  To do this,
a special <tt>%typemap</tt> directive is used.  For example:
</p>

<div class="code">
<pre>
/* Convert from Python --&gt; C */
%typemap(in) int {
    $1 = PyInt_AsLong($input);
}

/* Convert from C --&gt; Python */
%typemap(out) int {
    $result = PyInt_FromLong($1);
}
</pre>
</div>

<p>
At first glance, this code will look a little confusing.
However, there is really not much to it.  The first typemap (the "in"
typemap) is used to convert a value from the target language to C.  The second
typemap (the "out" typemap) is used to convert in the other
direction. The content of each typemap is a small fragment of code
that is inserted directly into the SWIG generated wrapper functions.
The code is usually C or C++ code which will be generated into the C/C++ wrapper functions.
Note that this isn't always the case as some target language modules allow target language 
code within the typemaps which gets generated into target language specific files.
Within this code, a number of special variables prefixed with a $ are expanded.  These are
really just placeholders for C/C++ variables that are generated in the course
of creating the wrapper function. In this case, <tt>$input</tt> refers to an
input object that needs to be converted to C/C++ and <tt>$result</tt>
refers to an object that is going to be returned by a wrapper
function.  <tt>$1</tt> refers to a C/C++ variable that has the same type as
specified in the typemap declaration (an <tt>int</tt> in this
example).
</p>

<p>
A short example might make this a little more clear.  If you were wrapping a
function like this:
</p>

<div class="code">
<pre>
int gcd(int x, int y);
</pre>
</div>

<p>
A wrapper function would look approximately like this:
</p>

<div class="code">
<pre>
PyObject *wrap_gcd(PyObject *self, PyObject *args) {
   int arg1;
   int arg2;
   int result;
   PyObject *obj1;
   PyObject *obj2;
   PyObject *resultobj;

   if (!PyArg_ParseTuple("OO:gcd", &amp;obj1, &amp;obj2)) return NULL;

   /* "in" typemap, argument 1 */<b>   
   {
      arg1 = PyInt_AsLong(obj1);
   }
</b>
   /* "in" typemap, argument 2 */<b>
   {
      arg2 = PyInt_AsLong(obj2);
   }
</b>
   result = gcd(arg1,arg2);

   /* "out" typemap, return value */<b>
   {
      resultobj = PyInt_FromLong(result);
   }
</b>
   return resultobj;
}
</pre>
</div>

<p>
In this code, you can see how the typemap code has been inserted into
the function.  You can also see how the special $ variables have been
expanded to match certain variable names inside the wrapper function.  This is really the
whole idea behind typemaps--they simply let you insert arbitrary code into different 
parts of the generated wrapper functions.   Because arbitrary code can be inserted, it
possible to completely change the way in which values are converted.
</p>

<H3><a name="Typemaps_nn5"></a>11.1.3 Pattern matching</H3>


<p>
As the name implies, the purpose of a typemap is to "map" C datatypes to 
types in the target language.   Once a typemap is defined for a C datatype,
it is applied to all future occurrences of that type in the input file.  For example:
</p>

<div class="code">
<pre>
/* Convert from Perl --&gt; C */
%typemap(in) <b>int</b> {
   $1 = SvIV($input);
}

...
int factorial(<b>int</b> n);
int gcd(<b>int</b> x, <b>int</b> y);
int count(char *s, char *t, <b>int</b> max);
</pre>
</div>

<p>
The matching of typemaps to C datatypes is more than a simple textual match.  In fact,
typemaps are fully built into the underlying type system.  Therefore, typemaps are
unaffected by <tt>typedef</tt>, namespaces, and other declarations that might hide the
underlying type.  For example, you could have code like this:
</p>

<div class="code">
<pre>
/* Convert from Ruby--&gt; C */
%typemap(in) <b>int</b> {
   $1 = NUM2INT($input);
}
...
typedef int Integer;
namespace foo {
    typedef Integer Number;
};

int foo(<b>int</b> x);
int bar(<b>Integer</b> y);
int spam(<b>foo::Number</b> a, <b>foo::Number</b> b);
</pre>
</div>

<p>
In this case, the typemap is still applied to the proper arguments even though typenames don't always
match the text "int".  This ability to track types is a critical part of SWIG--in fact, all
of the target language modules work merely define a set of typemaps for the basic types.  Yet, it
is never necessary to write new typemaps for typenames introduced by <tt>typedef</tt>.
</p>

<p>
In addition to tracking typenames, typemaps may also be specialized to match against a specific argument name.  For
example, you could write a typemap like this:
</p>

<div class="code">
<pre>
%typemap(in) <b>double nonnegative</b> {
   $1 = PyFloat_AsDouble($input);
   if ($1 &lt; 0) {
        PyErr_SetString(PyExc_ValueError,"argument must be nonnegative.");
        return NULL;
   }
}

...
double sin(double x);
double cos(double x);
double sqrt(<b>double nonnegative</b>);

typedef double Real;
double log(<b>Real nonnegative</b>);
...
</pre>
</div>

<p>
For certain tasks such as input argument conversion, typemaps can be defined for sequences of
consecutive arguments.    For example:
</p>

<div class="code">
<pre>
%typemap(in) (<b>char *str, int len</b>) {
    $1 = PyString_AsString($input);   /* char *str */
    $2 = PyString_Size($input);       /* int len   */
}
...
int count(<b>char *str, int len</b>, char c);
</pre>
</div>

<p>
In this case, a single input object is expanded into a pair of C arguments.  This example also
provides a hint to the unusual variable naming scheme involving <tt>$1</tt>, <tt>$2</tt>, and so forth.
</p>

<H3><a name="Typemaps_nn6"></a>11.1.4 Reusing typemaps</H3>


<p>
Typemaps are normally defined for specific type and argument name patterns.  However, typemaps can also 
be copied and reused.  One way to do this is to use assignment like this:
</p>

<div class="code">
<pre>
%typemap(in) Integer = int;   
%typemap(in) (char *buffer, int size) = (char *str, int len);
</pre>
</div>

<p>
A more general form of copying is found in the <tt>%apply</tt> directive like this:
</p>

<div class="code">
<pre>
%typemap(in) int {
   /* Convert an integer argument */
   ...
}
%typemap(out) int {
   /* Return an integer value */
   ...
}

/* Apply all of the integer typemaps to size_t */
%apply int { size_t };    
</pre>
</div>

<p>
<tt>%apply</tt> merely takes <em>all</em> of the typemaps that are defined for one type and
applies them to other types.  Note: you can include a comma separated set of types in the 
<tt>{ ... }</tt> part of <tt>%apply</tt>.
</p>

<p>
It should be noted that it is not necessary to copy typemaps for types that are related by <tt>typedef</tt>.
For example, if you have this,
</p>

<div class="code">
<pre>
typedef int size_t;
</pre>
</div>

<p>
then SWIG already knows that the <tt>int</tt> typemaps apply.  You don't have to do anything.
</p>

<H3><a name="Typemaps_nn7"></a>11.1.5 What can be done with typemaps?</H3>


<p>
The primary use of typemaps is for defining wrapper generation behavior at the level
of individual C/C++ datatypes.  There are currently six general categories of problems that
typemaps address:
</p>

<p>
<b>Argument handling</b>
</p>

<div class="code">
<pre>
int foo(<b>int x, double y, char *s</b>);
</pre>
</div>

<ul>
<li>Input argument conversion ("in" typemap).</li>
<li>Input argument type checking ("typecheck" typemap).</li>
<li>Output argument handling ("argout" typemap).</li>
<li>Input argument value checking ("check" typemap).</li>
<li>Input argument initialization ("arginit" typemap).</li>
<li>Default arguments ("default" typemap).</li>
<li>Input argument resource management ("freearg" typemap).</li>
</ul>

<p>
<b>Return value handling</b>
</p>

<div class="code">
<pre>
<b>int</b> foo(int x, double y, char *s);
</pre>
</div>

<ul>
<li>Function return value conversion ("out" typemap).</li>
<li>Return value resource management ("ret" typemap).</li>
<li>Resource management for newly allocated objects ("newfree" typemap).</li>
</ul>

<p>
<b>Exception handling</b>
</p>

<div class="code">
<pre>
<b>int</b> foo(int x, double y, char *s) throw(<b>MemoryError, IndexError</b>);
</pre>
</div>

<ul>
<li>Handling of C++ exception specifications. ("throw" typemap).</li>
</ul>

<p>
<b>Global variables</b>
</p>

<div class="code">
<pre>
<b>int foo;</b>
</pre>
</div>

<ul>
<li>Assignment of a global variable. ("varin" typemap).</li>
<li>Reading a global variable. ("varout" typemap).</li>
</ul>

<p>
<b>Member variables</b>
</p>

<div class="code">
<pre>
struct Foo {
    <b>int x[20]</b>;
};
</pre>
</div>

<ul>
<li>Assignment of data to a class/structure member. ("memberin" typemap).</li>
</ul>

<p>
<b>Constant creation</b>
</p>

<div class="code">
<pre>
#define FOO 3
%constant int BAR = 42;
enum { ALE, LAGER, STOUT };
</pre>
</div>

<ul>
<li>Creation of constant values. ("consttab" or "constcode" typemap).</li>
</ul>

<p>
Details of each of these typemaps will be covered shortly.  Also, certain language modules may define additional
typemaps that expand upon this list.  For example, the Java module defines a variety of typemaps for controlling additional
aspects of the Java bindings.  Consult language specific documentation for further details.
</p>

<H3><a name="Typemaps_nn8"></a>11.1.6 What can't be done with typemaps?</H3>


<p>
Typemaps can't be used to define properties that apply to C/C++ declarations as a whole.  For example,
suppose you had a declaration like this,
</p>

<div class="code">
<pre>
Foo *make_Foo(int n);
</pre>
</div>

<p>
and you wanted to tell SWIG that <tt>make_Foo(int n)</tt> returned a newly
allocated object (for the purposes of providing better memory
management).  Clearly, this property of <tt>make_Foo(int n)</tt> is
<em>not</em> a property that would be associated with the datatype
<tt>Foo *</tt> by itself.  Therefore, a completely different SWIG
customization mechanism (<tt>%feature</tt>) is used for this purpose.  Consult the <a
href="Customization.html#Customization">Customization Features</a> chapter for more
information about that.
</p>

<p>
Typemaps also can't be used to rearrange or transform the order of arguments.  For example,
if you had a function like this:
</p>

<div class="code">
<pre>
void foo(int, char *);
</pre>
</div>

<p>
you can't use typemaps to interchange the arguments, allowing you to call the
function like this:
</p>

<div class="targetlang">
<pre>
foo("hello",3)          # Reversed arguments
</pre>
</div>

<p>
If you want to change the calling conventions of a function, write a helper
function instead.  For example:
</p>

<div class="code">
<pre>
%rename(foo) wrap_foo;
%inline %{
void wrap_foo(char *s, int x) {
   foo(x,s);
}
%}
</pre>
</div>

<H3><a name="Typemaps_aspects"></a>11.1.7 Similarities to Aspect Oriented Programming</H3>


<p>
SWIG has parallels to <a href="http://en.wikipedia.org/wiki/Aspect-oriented_programming">Aspect Oriented Software Development (AOP)</a>.
The <a href="http://en.wikipedia.org/wiki/Aspect-oriented_programming#Terminology">AOP terminology</a> with respect to SWIG typemaps can be viewed as follows:
</p>
<ul>
  <li> <b>Cross-cutting concerns</b>: The cross-cutting concerns are the modularization of the functionality that the typemaps implement, which is primarily marshalling of types from/to the target language and C/C++.
  <li> <b>Advice</b>: The typemap body contains code which is executed whenever the marshalling is required.
  <li> <b>Pointcut</b>: The pointcuts are the positions in the wrapper code that the typemap code is generated into.
  <li> <b>Aspect</b>: Aspects are the combination of the pointcut and the advice, hence each typemap is an aspect.
</ul>
<p>
SWIG can also be viewed as has having a second set of aspects based around <a href="Customization.html">%feature</a>.
Features such as <tt>%exception</tt> are also cross-cutting concerns as they encapsulate code that can be used to add logging or exception handling to any function.
</p>

<H3><a name="Typemaps_nn9"></a>11.1.8 The rest of this chapter</H3>


<p>
The rest of this chapter provides detailed information for people who
want to write new typemaps.  This information is of particular importance to anyone
who intends to write a new SWIG target language module.  Power users can also
use this information to write application specific type conversion rules.
</p>

<p>
Since typemaps are strongly tied to the underlying C++ type system,
subsequent sections assume that you are reasonably familiar with the
basic details of values, pointers, references, arrays, type qualifiers
(e.g., <tt>const</tt>), structures, namespaces, templates, and memory
management in C/C++.   If not, you would be well-advised to consult a copy 
of "The C Programming Language" by Kernighan and Ritchie or 
"The C++ Programming Language" by Stroustrup before going any further.
</p>

<H2><a name="Typemaps_nn10"></a>11.2 Typemap specifications</H2>


<p>
This section describes the behavior of the <tt>%typemap</tt> directive itself.
</p>

<H3><a name="Typemaps_defining"></a>11.2.1 Defining a typemap</H3>


<p>
New typemaps are defined using the <tt>%typemap</tt> declaration.  The general form of
this declaration is as follows (parts enclosed in [ ... ] are optional):
</p>

<div class="code">
<pre>
%typemap(<em>method</em> [, <em>modifiers</em>]) <em>typelist</em> <em>code</em> ;
</pre>
</div>

<p>
<em>method</em> is a simply a name that specifies what kind of typemap is being defined.  It
is usually a name like <tt>"in"</tt>, <tt>"out"</tt>, or <tt>"argout"</tt>.   The purpose of
these methods is described later.
</p>

<p>
<em>modifiers</em> is an optional comma separated list of <tt>name="value"</tt> values. 
These are sometimes to attach extra information to a typemap and is often target-language dependent.
They are also known as typemap attributes.
</p>

<p>
<em>typelist</em> is a list of the C++ type patterns that the typemap will match.   The general form of
this list is as follows:
</p>

<div class="diagram">
<pre>
typelist    :  typepattern [, typepattern, typepattern, ... ] ;

typepattern :  type [ (parms) ]
            |  type name [ (parms) ]
            |  ( typelist ) [ (parms) ]

</pre>
</div>

<p>
Each type pattern is either a simple type, a simple type and argument name, or a list of types in the
case of multi-argument typemaps. In addition, each type pattern can be parameterized with a list of temporary
variables (parms).   The purpose of these variables will be explained shortly.
</p>

<p><em>code</em> specifies the code used in the typemap.
Usually this is C/C++ code, but in the statically typed target languages, such as Java and C#, this can contain target language code for certain typemaps.
It can take any one of the following forms:
</p>

<div class="diagram">
<pre>
code       : { ... }
           | " ... "
           | %{ ... %}
</pre>
</div>

<p>
Note that the preprocessor will expand code within the {} delimiters, but not in the last two styles of delimiters,
see <a href="Preprocessor.html#Preprocessor_typemap_delimiters">Preprocessor and Typemaps</a>.
Here are some examples of valid typemap specifications:
</p>

<div class="code">
<pre>
/* Simple typemap declarations */
%typemap(in) int {
   $1 = PyInt_AsLong($input);
}
%typemap(in) int "$1 = PyInt_AsLong($input);";
%typemap(in) int %{ 
   $1 = PyInt_AsLong($input);
%}

/* Typemap with extra argument name */
%typemap(in) int nonnegative {
   ...
}

/* Multiple types in one typemap */
%typemap(in) int, short, long { 
   $1 = SvIV($input);
}

/* Typemap with modifiers */
%typemap(in,doc="integer") int "$1 = scm_to_int($input);";

/* Typemap applied to patterns of multiple arguments */
%typemap(in) (char *str, int len),
             (char *buffer, int size)
{
   $1 = PyString_AsString($input);
   $2 = PyString_Size($input);
}

/* Typemap with extra pattern parameters */
%typemap(in, numinputs=0) int *output (int temp),
                          long *output (long temp)
{
   $1 = &amp;temp;
}
</pre>
</div>

<p>
Admittedly, it's not the most readable syntax at first glance.  However, the purpose of the
individual pieces will become clear.
</p>

<H3><a name="Typemaps_nn12"></a>11.2.2 Typemap scope</H3>


<p>
Once defined, a typemap remains in effect for all of the declarations that follow.  A typemap may be redefined for
different sections of an input file.  For example:
</p>

<div class="code">
<pre>
// typemap1
%typemap(in) int {
...
}

int fact(int);                    // typemap1
int gcd(int x, int y);            // typemap1

// typemap2
%typemap(in) int {
...
}

int isprime(int);                 // typemap2
</pre>
</div>

<p>
One exception to the typemap scoping rules pertains to the <tt>%extend</tt> declaration.  <tt>%extend</tt> is used to attach
new declarations to a class or structure definition.  Because of this, all of the declarations in an <tt>%extend</tt> block are
subject to the typemap rules that are in effect at the point where the class itself is defined.  For example:
</p>

<div class="code">
<pre>
class Foo {
   ...
};

%typemap(in) int {
 ...
}

%extend Foo {
   int blah(int x);    // typemap has no effect.  Declaration is attached to Foo which 
                       // appears before the %typemap declaration.
};
</pre>
</div>

<H3><a name="Typemaps_nn13"></a>11.2.3 Copying a typemap</H3>


<p>
A typemap is copied by using assignment.   For example:
</p>

<div class="code">
<pre>
%typemap(in) Integer = int;
</pre>
</div>

<p>
or this:
</p>

<div class="code">
<pre>
%typemap(in) Integer, Number, int32_t = int;
</pre>
</div>

<p>
Types are often managed by a collection of different typemaps.  For example:
</p>

<div class="code">
<pre>
%typemap(in)     int { ... }
%typemap(out)    int { ... }
%typemap(varin)  int { ... }
%typemap(varout) int { ... }
</pre>
</div>

<p>
To copy all of these typemaps to a new type, use <tt>%apply</tt>.  For example:
</p>

<div class="code">
<pre>
%apply int { Integer };            // Copy all int typemaps to Integer
%apply int { Integer, Number };    // Copy all int typemaps to both Integer and Number
</pre>
</div>

<p>
The patterns for <tt>%apply</tt> follow the same rules as for <tt>%typemap</tt>. For example:
</p>

<div class="code">
<pre>
%apply int *output { Integer *output };                    // Typemap with name
%apply (char *buf, int len) { (char *buffer, int size) };  // Multiple arguments
</pre>
</div>

<H3><a name="Typemaps_nn14"></a>11.2.4 Deleting a typemap</H3>


<p>
A typemap can be deleted by simply defining no code.  For example:
</p>

<div class="code">
<pre>
%typemap(in) int;               // Clears typemap for int
%typemap(in) int, long, short;  // Clears typemap for int, long, short
%typemap(in) int *output;       
</pre>
</div>

<p>
The <tt>%clear</tt> directive clears all typemaps for a given type.
For example:
</p>

<div class="code">
<pre>
%clear int;                     // Removes all types for int
%clear int *output, long *output;
</pre>
</div>

<p>
<b>Note:</b> Since SWIG's default behavior is defined by typemaps, clearing a fundamental type like
<tt>int</tt> will make that type unusable unless you also define a new set of typemaps immediately
after the clear operation.
</p>

<H3><a name="Typemaps_nn15"></a>11.2.5 Placement of typemaps</H3>


<p>
Typemap declarations can be declared in the global scope, within a C++ namespace, and within a C++ class.  For
example:
</p>

<div class="code">
<pre>
%typemap(in) int {
   ...
}

namespace std {
    class string;
    %typemap(in) string {
        ...
    }
}

class Bar {
public:
    typedef const int &amp; const_reference;
    %typemap(out) const_reference {
         ...
    }
};
</pre>
</div>

<p>
When a typemap appears inside a namespace or class, it stays in effect until the end of the SWIG input 
(just like before). However, the typemap takes the local scope into account.   Therefore, this
code
</p>

<div class="code">
<pre>
namespace std {
    class string;
    %typemap(in) string {
       ...
    }
}
</pre>
</div>

<p>
is really defining a typemap for the type <tt>std::string</tt>.   You could have code like this:
</p>

<div class="code">
<pre>
namespace std {
    class string;
    %typemap(in) string {          /* std::string */
       ...
    }
}

namespace Foo {
    class string;
    %typemap(in) string {          /* Foo::string */
       ...
    }
}
</pre>
</div>

<p>
In this case, there are two completely distinct typemaps that apply to two completely different
types (<tt>std::string</tt> and <tt>Foo::string</tt>).
</p>

<p>
It should be noted that for scoping to work, SWIG has to know that <tt>string</tt> is a typename defined
within a particular namespace.  In this example, this is done using the forward class declaration <tt>class string</tt>.
</p>

<H2><a name="Typemaps_pattern_matching"></a>11.3 Pattern matching rules</H2>


<p>
The section describes the pattern matching rules by which C/C++ datatypes are associated with typemaps.
The matching rules can be observed in practice by using the debugging options also described.
</p>

<H3><a name="Typemaps_nn17"></a>11.3.1 Basic matching rules</H3>


<p>
Typemaps are matched using both a type and a name (typically the name of a argument).  For a given
<tt>TYPE NAME</tt> pair, the following rules are applied, in order, to find a match.  The first typemap found
is used.
</p>

<ul>
<li>Typemaps that exactly match <tt>TYPE</tt> and <tt>NAME</tt>.
<li>Typemaps that exactly match <tt>TYPE</tt> only.
<li>If <tt>TYPE</tt> is a C++ template of type <tt>T&lt; TPARMS &gt;</tt>, where <tt>TPARMS</tt> are the template parameters,
    the type is stripped of the template parameters and the following checks are then made:
  <ul>
    <li>Typemaps that exactly match <tt>T</tt> and <tt>NAME</tt>.
    <li>Typemaps that exactly match <tt>T</tt> only.
  </ul>
</ul>

<p>
If <tt>TYPE</tt> includes qualifiers (const, volatile, etc.), each qualifier is stripped one at a time to form a new stripped type 
and the matching rules above are repeated on the stripped type.
The left-most qualifier is stripped first, resulting in the right-most (or top-level) qualifier being stripped last.
For example <tt>int const*const</tt> is first stripped to <tt>int *const</tt> then <tt>int *</tt>.
</p>

<p>
If <tt>TYPE</tt> is an array.  The following transformation is made:
</p>

<ul>
<li>Replace all dimensions to <tt>[ANY]</tt> and look for a generic array typemap.
</ul>

<p>
To illustrate, suppose that you had a function like this:
</p>

<div class="code">
<pre>
int foo(const char *s);
</pre>
</div>

<p>
To find a typemap for the argument <tt>const char *s</tt>, SWIG will search for the following typemaps:
</p>

<div class="diagram">
<pre>
const char *s           Exact type and name match
const char *            Exact type match
char *s                 Type and name match (qualifier stripped)
char *                  Type match (qualifier stripped)
</pre>
</div>

<p>
When more than one typemap rule might be defined, only the first match
found is actually used.  Here is an example that
shows how some of the basic rules are applied:
</p>

<div class="code"><pre>
%typemap(in) int *x {
   ... typemap 1
}

%typemap(in) int * {
   ... typemap 2
}

%typemap(in) const int *z {
   ... typemap 3
}

%typemap(in) int [4] {
   ... typemap 4
}

%typemap(in) int [ANY] {
   ... typemap 5
}

void A(int *x);        // int *x rule       (typemap 1)
void B(int *y);        // int * rule        (typemap 2)
void C(const int *x);  // int *x rule       (typemap 1)
void D(const int *z);  // const int *z rule (typemap 3)
void E(int x[4]);      // int [4] rule      (typemap 4)
void F(int x[1000]);   // int [ANY] rule    (typemap 5)
</pre>
</div>

<p>
<b>Compatibility note: </b> SWIG-2.0.0 introduced stripping the qualifiers one step at a time. Prior versions
stripped all qualifiers in one step.
</p>

<H3><a name="Typemaps_typedef_reductions"></a>11.3.2 Typedef reductions matching</H3>


<p>
If no match is found using the rules in the previous section, SWIG
applies a typedef reduction to the type and repeats the typemap search
for the reduced type.   To illustrate, suppose you had code like this:
</p>

<div class="code">
<pre>
%typemap(in) int {
   ... typemap 1
}

typedef int Integer;
void blah(Integer x);
</pre>
</div>

<p>
To find the typemap for <tt>Integer x</tt>, SWIG will first search for the following
typemaps:
</p>

<div class="diagram">
<pre>
Integer x
Integer
</pre>
</div>

<p>
Finding no match, it then applies a reduction <tt>Integer -&gt; int</tt> to the type and
repeats the search.
</p>

<div class="diagram">
<pre>
int x
int      --&gt; match: typemap 1
</pre>
</div>

<p>
Even though two types might be the same via typedef, SWIG allows typemaps to be defined 
for each typename independently.  This allows for interesting customization possibilities based
solely on the typename itself.  For example, you could write code like this:
</p>

<div class="code">
<pre>
typedef double  pdouble;     // Positive double

// typemap 1
%typemap(in) double {
   ... get a double ...
}
// typemap 2
%typemap(in) pdouble {
   ... get a positive double ...
}
double sin(double x);           // typemap 1
pdouble sqrt(pdouble x);        // typemap 2
</pre>
</div>

<p>
When reducing the type, only one typedef reduction is applied at a
time.  The search process continues to apply reductions until a
match is found or until no more reductions can be made.
</p>

<p>
For complicated types, the reduction process can generate a long list of patterns.  Consider the following:
</p>

<div class="code">
<pre>
typedef int Integer;
typedef Integer Row4[4];
void foo(Row4 rows[10]);
</pre>
</div>

<p>
To find a match for the <tt>Row4 rows[10]</tt> argument, SWIG would
check the following patterns, stopping only when it found a match:
</p>

<div class="code">
<pre>
Row4 rows[10]
Row4 [10]
Row4 rows[ANY]
Row4 [ANY]

# Reduce Row4 --&gt; Integer[4]
Integer rows[10][4]
Integer [10][4]
Integer rows[ANY][ANY]
Integer [ANY][ANY]

# Reduce Integer --&gt; int
int rows[10][4]
int [10][4]
int rows[ANY][ANY]
int [ANY][ANY]
</pre>
</div>

<p>
For parameterized types like templates, the situation is even more complicated.  Suppose you had some declarations
like this:
</p>

<div class="code">
<pre>
typedef int Integer;
typedef foo&lt;Integer,Integer&gt; fooii;
void blah(fooii *x);
</pre>
</div>

<p>
In this case, the following typemap patterns are searched for the argument <tt>fooii *x</tt>:
</p>

<div class="code">
<pre>
fooii *x
fooii *

# Reduce fooii --&gt; foo&lt;Integer,Integer&gt;
foo&lt;Integer,Integer&gt; *x
foo&lt;Integer,Integer&gt; *

# Reduce Integer -&gt; int
foo&lt;int, Integer&gt; *x
foo&lt;int, Integer&gt; *

# Reduce Integer -&gt; int
foo&lt;int, int&gt; *x
foo&lt;int, int&gt; *
</pre>
</div>

<p>
Typemap reductions are always applied to the left-most type that appears.  Only when no reductions can be made to the left-most
type are reductions made to other parts of the type.   This behavior means that you could define a typemap for
<tt>foo&lt;int,Integer&gt;</tt>, but a typemap for <tt>foo&lt;Integer,int&gt;</tt> would never be matched.  Admittedly, this
is rather esoteric--there's little practical reason to write a typemap quite like that.  Of course, you could rely on this
to confuse your coworkers even more.
</p>

<p>
As a point of clarification, it is worth emphasizing that typedef matching is a typedef <b>reduction</b> process only, that is, SWIG does not search for every single possible typedef.
Given a type in a declaration, it will only reduce the type, it won't build it up looking for typedefs.
For example, given the type <tt>Struct</tt>, the typemap below will not be used for the <tt>aStruct</tt> parameter,
because <tt>Struct</tt> is fully reduced:
</p>

<div class="code">
<pre>
struct Struct {...};
typedef Struct StructTypedef;

%typemap(in) StructTypedef { 
  ...
}

void go(Struct aStruct);
</pre>
</div>

<H3><a name="Typemaps_nn19"></a>11.3.3 Default typemap matching rules</H3>


<p>
If the basic pattern matching rules result in no match being made, even after typedef reductions,
the default typemap matching rules are used to look for a suitable typemap match.
These rules match a generic typemap based on the reserved <tt>SWIGTYPE</tt> base type.
For example pointers will use <tt>SWIGTYPE *</tt> and references will use <tt>SWIGTYPE &amp;</tt>.
More precisely, the rules are based on the C++ class template partial specialization matching rules used
by C++ compilers when looking for an appropriate partial template specialization.
This means that a match is chosen from the most specialized set of generic typemap types available. For example,
when looking for a match to <tt>int const *</tt>, the rules will prefer to match <tt>SWIGTYPE const *</tt>
if available before matching <tt>SWIGTYPE *</tt>, before matching <tt>SWIGTYPE</tt>.
</p>

<p>
Most SWIG language modules use typemaps to define the default behavior of the C primitive types.  This
is entirely straightforward.  For example, a set of typemaps for primitives marshalled by value or
const reference are written like this:
</p>

<div class="code">
<pre>
%typemap(in) int           "... convert to int ...";
%typemap(in) short         "... convert to short ...";
%typemap(in) float         "... convert to float ...";
...
%typemap(in) const int &amp;   "... convert ...";
%typemap(in) const short &amp; "... convert ...";
%typemap(in) const float &amp; "... convert ...";
...
</pre>
</div>

<p>
Since typemap matching follows all <tt>typedef</tt> declarations, any sort of type that is
mapped to a primitive type by value or const reference through <tt>typedef</tt> will be picked
up by one of these primitive typemaps.
Most language modules also define typemaps for char pointers and char arrays to handle strings,
so these non-default types will also be used in preference as the basic typemap matching rules
provide a better match than the default typemap matching rules.
</p>

<p>
Below is a list of the typical default types supplied by language modules, showing what the "in" typemap would look like:
</p>

<div class="code">
<pre>
%typemap(in) SWIGTYPE &amp;            { ... default reference handling ...                       };
%typemap(in) SWIGTYPE *            { ... default pointer handling ...                         };
%typemap(in) SWIGTYPE *const       { ... default pointer const handling ...                   };
%typemap(in) SWIGTYPE *const&amp;      { ... default pointer const reference handling ...         };
%typemap(in) SWIGTYPE[ANY]         { ... 1D fixed size arrays handlling ...                   };
%typemap(in) SWIGTYPE []           { ... unknown sized array handling ...                     };
%typemap(in) enum SWIGTYPE         { ... default handling for enum values ...                 };
%typemap(in) const enum SWIGTYPE &amp; { ... default handling for const enum reference values ... };
%typemap(in) SWIGTYPE (CLASS::*)   { ... default pointer member handling ...                  };
%typemap(in) SWIGTYPE              { ... simple default handling ...                          };
</pre>
</div>

<p>
If you wanted to change SWIG's default handling for
simple pointers, you would simply redefine the rule for <tt>SWIGTYPE *</tt>.
Note, the simple default typemap rule is used to match against simple types that don't match any other rules:
</p>

<div class="code">
<pre>
%typemap(in) SWIGTYPE              { ... simple default handling ...                          } 
</pre>
</div>

<p>
This typemap is important because it is the rule that gets triggered
when call or return by value is used.  For instance, if you have a
declaration like this:
</p>

<div class="code">
<pre>
double dot_product(Vector a, Vector b);
</pre>
</div>

<p>
The <tt>Vector</tt> type will usually just get matched against
<tt>SWIGTYPE</tt>. The default implementation of <tt>SWIGTYPE</tt> is
to convert the value into pointers (<a href="SWIG.html#SWIG_nn22">as described in this earlier section</a>).
</p>

<p>
By redefining <tt>SWIGTYPE</tt> it may be possible to implement other
behavior.  For example, if you cleared all typemaps for
<tt>SWIGTYPE</tt>, SWIG simply won't wrap any unknown datatype (which might
be useful for debugging).   Alternatively, you might modify SWIGTYPE to marshal
objects into strings instead of converting them to pointers.
</p>

<p>
Let's consider an example where the following typemaps are defined and SWIG is looking for the best match for the enum shown below:
</p>

<div class="code">
<pre>
%typemap(in) const Hello &amp;          { ... }
%typemap(in) const enum SWIGTYPE &amp;  { ... }
%typemap(in) enum SWIGTYPE &amp;        { ... }
%typemap(in) SWIGTYPE &amp;             { ... }
%typemap(in) SWIGTYPE               { ... }

enum Hello {};
const Hello &amp;hi;
</pre>
</div>

<p>
The typemap at the top of the list will be chosen, not because it is defined first, but because it is the closest match for the type being wrapped.
If any of the typemaps in the above list were not defined, then the next one on the list would have precedence.
</p>

<p>
The best way to explore the default typemaps is to look at the ones
already defined for a particular language module.  Typemap
definitions are usually found in the SWIG library in a file such as
<tt>java.swg</tt>, <tt>csharp.swg</tt> etc.
However, for many of the target languages the typemaps are hidden behind complicated macros,
so the best way to view the default typemaps, or any typemaps for that matter, 
is to look at the preprocessed output by running <tt>swig -E</tt> on any interface file.
Finally the best way to view the typemap matching rules in action is via the <a href="#Typemaps_debugging_search">debugging typemap pattern matching</a> options covered later on.
</p>

<p>
<b>Compatibility note: </b> The default typemap matching rules were modified in SWIG-2.0.0 from a slightly 
simpler scheme to match the current C++ class template partial specialization matching rules.
</p>

<H3><a name="Typemaps_multi_argument_typemaps_patterns"></a>11.3.4 Multi-arguments typemaps</H3>


<p>
When multi-argument typemaps are specified, they take precedence over
any typemaps specified for a single type.  For example:
</p>

<div class="code">
<pre>
%typemap(in) (char *buffer, int len) {
   // typemap 1
}

%typemap(in) char *buffer {
   // typemap 2
}

void foo(char *buffer, int len, int count); // (char *buffer, int len)
void bar(char *buffer, int blah);           // char *buffer
</pre>
</div>

<p>
Multi-argument typemaps are also more restrictive in the way that they are matched.
Currently, the first argument follows the matching rules described in the previous section,
but all subsequent arguments must match exactly.
</p>


<H3><a name="Typemaps_matching_template_comparison"></a>11.3.5 Matching rules compared to C++ templates</H3>


<p>
For those intimately familiar with C++ templates, a comparison of the typemap matching rules and template type deduction is interesting.
The two areas considered are firstly the default typemaps and their similarities to partial template specialization and secondly, non-default typemaps and their similarities to full template specialization.
</p>

<p>
For default (SWIGTYPE) typemaps the rules are inspired by C++ class template
partial specialization. For example, given partial specialization for <tt>T const&amp;</tt> :
</p>

<div class="code">
<pre>
template &lt;typename T&gt; struct X             { void a(); };
template &lt;typename T&gt; struct X&lt; T const&amp; &gt; { void b(); };
</pre>
</div>

<p>
The full (unspecialized) template is matched with most types, such as:
</p>

<div class="code">
<pre>
X&lt; int &amp; &gt;            x1;  x1.a();
</pre>
</div>

<p>
and the following all match the <tt>T const&amp;</tt> partial specialization:
</p>

<div class="code">
<pre>
X&lt; int *const&amp; &gt;      x2;  x2.b();
X&lt; int const*const&amp; &gt; x3;  x3.b();
X&lt; int const&amp; &gt;       x4;  x4.b();
</pre>
</div>

<p>
Now, given just these two default typemaps, where T is analogous to SWIGTYPE:
</p>

<div class="code">
<pre>
%typemap(...) SWIGTYPE        { ... }
%typemap(...) SWIGTYPE const&amp; { ... }
</pre>
</div>

<p>
The generic default typemap <tt>SWIGTYPE</tt> is used with most types, such as
</p>

<div class="code">
<pre>
int &amp;
</pre>
</div>

<p>
and the following all match the <tt>SWIGTYPE const&amp;</tt> typemap, just like the partial template matching:
</p>

<div class="code">
<pre>
int *const&amp;
int const*const&amp;
int const&amp;
</pre>
</div>

<p>
Note that the template and typemap matching rules are not identical for all default typemaps though, for example, with arrays.
</p>

<p>
For non-default typemaps, one might expect SWIG to follow the fully specialized template rules.
This is nearly the case, but not quite.
Consider a very similar example to the earlier partially specialized template but this time there is a fully specialized template:
</p>

<div class="code">
<pre>
template &lt;typename T&gt; struct Y       { void a(); };
template &lt;&gt; struct Y&lt; int const &amp; &gt;  { void b(); };
</pre>
</div>

<p>
Only the one type matches the specialized template exactly:
</p>

<div class="code">
<pre>
Y&lt; int &amp; &gt;             y1;  y1.a();
Y&lt; int *const&amp; &gt;       y2;  y2.a();
Y&lt; int const *const&amp; &gt; y3;  y3.a();
Y&lt; int const&amp; &gt;        y4;  y4.b(); // fully specialized match
</pre>
</div>

<p>
Given typemaps with the same types used for the template declared above, where T is again analogous to SWIGTYPE:
</p>

<div class="code">
<pre>
%typemap(...) SWIGTYPE        { ... }
%typemap(...) int const&amp;      { ... }
</pre>
</div>

<p>
The comparison between non-default typemaps and fully specialized single parameter templates turns out to be the same, as just the one type will match the non-default typemap:
</p>

<div class="code">
<pre>
int &amp;
int *const&amp;
int const*const&amp;
int const&amp;        // matches non-default typemap int const&amp;
</pre>
</div>

<p>
However, if a non-const type is used instead:
</p>

<div class="code">
<pre>
%typemap(...) SWIGTYPE        { ... }
%typemap(...) int &amp;           { ... }
</pre>
</div>

<p>
then there is a clear difference to template matching as both the const and non-const types match the typemap:
</p>

<div class="code">
<pre>
int &amp;             // matches non-default typemap int &amp;
int *const&amp;
int const*const&amp;
int const&amp;        // matches non-default typemap int &amp;
</pre>
</div>

<p>
There are other subtle differences such as typedef handling, but at least it should be clear that the typemap matching rules
are similar to those for specialized template handling.
</p>


<H3><a name="Typemaps_debugging_search"></a>11.3.6 Debugging typemap pattern matching</H3>


<p>
There are two useful debug command line options available for debugging typemaps, <tt>-debug-tmsearch</tt> and <tt>-debug-tmused</tt>.
</p>

<p>
The <tt>-debug-tmsearch</tt> option is a verbose option for debugging typemap searches.
This can be very useful for watching the pattern matching process in action and for debugging which typemaps are used.
The option displays all the typemaps and types that are looked for until a successful pattern match is made.
As the display includes searches for each and every type needed for wrapping, the amount of information displayed can be large.
Normally you would manually search through the displayed information for the particular type that you are interested in.
</p>

<p>
For example, consider some of the code used in the <a href="#Typemaps_typedef_reductions">Typedef reductions</a> section already covered:
</p>

<div class="code">
<pre>
typedef int Integer;
typedef Integer Row4[4];
void foo(Row4 rows[10]);
</pre>
</div>

<p>
A sample of the debugging output is shown below for the "in" typemap:
</p>

<div class="shell">
<pre>
swig -perl -debug-tmsearch example.i
...
example.h:3: Searching for a suitable 'in' typemap for: Row4 rows[10]
  Looking for: Row4 rows[10]
  Looking for: Row4 [10]
  Looking for: Row4 rows[ANY]
  Looking for: Row4 [ANY]
  Looking for: Integer rows[10][4]
  Looking for: Integer [10][4]
  Looking for: Integer rows[ANY][ANY]
  Looking for: Integer [ANY][ANY]
  Looking for: int rows[10][4]
  Looking for: int [10][4]
  Looking for: int rows[ANY][ANY]
  Looking for: int [ANY][ANY]
  Looking for: SWIGTYPE rows[ANY][ANY]
  Looking for: SWIGTYPE [ANY][ANY]
  Looking for: SWIGTYPE rows[ANY][]
  Looking for: SWIGTYPE [ANY][]
  Looking for: SWIGTYPE *rows[ANY]
  Looking for: SWIGTYPE *[ANY]
  Looking for: SWIGTYPE rows[ANY]
  Looking for: SWIGTYPE [ANY]
  Looking for: SWIGTYPE rows[]
  Looking for: SWIGTYPE []
  Using: %typemap(in) SWIGTYPE []
...
</pre>
</div>

<p>
showing that the best default match supplied by SWIG is the <tt>SWIGTYPE []</tt> typemap.
As the example shows, the successful match displays the used typemap source including typemap method, type and optional name in one of these simplified formats:
</p>

<ul>
  <li> <tt>Using: %typemap(method) type name</tt>
  <li> <tt>Using: %typemap(method) type name = type2 name2</tt>
  <li> <tt>Using: %apply type2 name2 { type name }</tt>
</ul>

<p>
This information might meet your debugging needs, however, you might want to analyze further.
If you next invoke SWIG with the <tt>-E</tt> option to display the preprocessed output, and search for the particular typemap used,
you'll find the full typemap contents (example shown below for Python):
</p>

<div class="code">
<pre>
%typemap(in, noblock=1) SWIGTYPE [] (void *argp = 0, int res = 0) {
  res = SWIG_ConvertPtr($input, &amp;argp,$descriptor, $disown |  0 );
  if (!SWIG_IsOK(res)) { 
    SWIG_exception_fail(SWIG_ArgError(res), "in method '" "$symname" "', argument "
                       "$argnum"" of type '" "$type""'"); 
  } 
  $1 = ($ltype)(argp);
}
</pre>
</div>

<p>
The generated code for the <tt>foo</tt> wrapper will then contain the snippets of the typemap with the special variables expanded.
The rest of this chapter will need reading though to fully understand all of this, however, the relevant parts of the generated code for the above typemap can be seen below:
</p>

<div class="code">
<pre>
SWIGINTERN PyObject *_wrap_foo(PyObject *SWIGUNUSEDPARM(self), PyObject *args) {
...
  void *argp1 = 0 ;
  int res1 = 0 ;
...
  res1 = SWIG_ConvertPtr(obj0, &amp;argp1,SWIGTYPE_p_a_4__int, 0 |  0 );
  if (!SWIG_IsOK(res1)) {
    SWIG_exception_fail(SWIG_ArgError(res1), "in method '" "foo" "', argument "
                       "1"" of type '" "int [10][4]""'"); 
  } 
  arg1 = (int (*)[4])(argp1);
...
}
</pre>
</div>

<p>
Searches for multi-argument typemaps are not mentioned unless a matching multi-argument typemap does actually exist.
For example, the output for the code in the <a href="#Typemaps_multi_argument_typemaps_patterns">earlier multi-arguments section</a> is as follows:
</p>

<div class="shell">
<pre>
...
example.h:39: Searching for a suitable 'in' typemap for: char *buffer
  Looking for: char *buffer
  Multi-argument typemap found...
  Using: %typemap(in) (char *buffer,int len)
...
</pre>
</div>

<p>
The second option for debugging is <tt>-debug-tmused</tt> and this displays the typemaps used.
This option is a less verbose version of the <tt>-debug-tmsearch</tt> option as it only displays each successfully found typemap on a separate single line.
The output displays the type, and name if present, the typemap method in brackets and then the actual typemap used in the same simplified format output by the <tt>-debug-tmsearch</tt> option.
Below is the output for the example code at the start of this section on debugging.
</p>

<div class="shell">
<pre>
$ swig -perl -debug-tmused example.i
example.h:3: Typemap for Row4 rows[10] (in) : %typemap(in) SWIGTYPE []
example.h:3: Typemap for Row4 rows[10] (typecheck) : %typemap(typecheck) SWIGTYPE *
example.h:3: Typemap for Row4 rows[10] (freearg) : %typemap(freearg) SWIGTYPE []
example.h:3: Typemap for void foo (out) : %typemap(out) void
</pre>
</div>

<p>
Now, consider the following interface file:
</p>

<div class="code">
<pre>
%module example

%{
void set_value(const char* val) {}
%}

%typemap(check) char *NON_NULL {
  if (!$1) {
    /* ... error handling ... */
  }
}

// use default pointer handling instead of strings
%apply SWIGTYPE * { const char* val, const char* another_value }

%typemap(check) const char* val = char* NON_NULL;

%typemap(arginit, noblock=1) const char* val {
   $1 = "";
}

void set_value(const char* val);

</pre>
</div>

<p>
and the output debug:
</p>

<div class="shell">
<pre>
swig -perl5 -debug-tmused example.i
example.i:21: Typemap for char const *val (arginit) : %typemap(arginit) char const *val
example.i:21: Typemap for char const *val (in) : %apply SWIGTYPE * { char const *val }
example.i:21: Typemap for char const *val (typecheck) : %apply SWIGTYPE * { char const *val }
example.i:21: Typemap for char const *val (check) : %typemap(check) char const *val = char *NON_NULL
example.i:21: Typemap for char const *val (freearg) : %apply SWIGTYPE * { char const *val }
example.i:21: Typemap for void set_value (out) : %typemap(out) void
</pre>
</div>

<p>
The following observations about what is displayed can be noted (the same applies for <tt>-debug-tmsearch</tt>):
</p>
<ul>
<li>
The relevant typemap is shown, but for typemap copying, the appropriate <tt>%typemap</tt> or <tt>%apply</tt> is displayed, for example, the "check" and "in" typemaps.
</li>
<li>
The typemap modifiers are not shown, eg the <tt>noblock=1</tt> modifier in the "arginit" typemap.
</li>
<li>
The exact <tt>%apply</tt> statement might look different to what is in the actual code. For example, the <tt>const char* another_value</tt> is not shown as it is not relevant here.
Also the types may be displayed slightly differently - <tt>char const *</tt> and not <tt>const char*</tt>.
</li>
</ul>

<H2><a name="Typemaps_nn21"></a>11.4 Code generation rules</H2>


<p>
This section describes rules by which typemap code is inserted into
the generated wrapper code.
</p>

<H3><a name="Typemaps_nn22"></a>11.4.1 Scope</H3>


<p>
When a typemap is defined like this:
</p>

<div class="code">
<pre>
%typemap(in) int {
   $1 = PyInt_AsLong($input);
}
</pre>
</div>

<p>
the typemap code is inserted into the wrapper function using a new block scope.  In other words, the
wrapper code will look like this:
</p>

<div class="code">
<pre>
wrap_whatever() {
    ...
    // Typemap code
    {                    
       arg1 = PyInt_AsLong(obj1);
    }
    ...
}
</pre>
</div>

<p>
Because the typemap code is enclosed in its own block, it is legal to declare temporary variables
for use during typemap execution.  For example:
</p>

<div class="code">
<pre>
%typemap(in) short {
   long temp;          /* Temporary value */
   if (Tcl_GetLongFromObj(interp, $input, &amp;temp) != TCL_OK) {
      return TCL_ERROR;
   }
   $1 = (short) temp;
}
</pre>
</div>

<p>
Of course, any variables that you declare inside a typemap are destroyed as soon as the typemap
code has executed (they are not visible to other parts of the wrapper function or other typemaps
that might use the same variable names).
</p>

<p>
Occasionally, typemap code will be specified using a few alternative forms.  For example:
</p>

<div class="code">
<pre>
%typemap(in) int "$1 = PyInt_AsLong($input);";
%typemap(in) int %{
$1 = PyInt_AsLong($input);
%}
%typemap(in, noblock=1) int {
$1 = PyInt_AsLong($input);
}
</pre>
</div>

<p>
These three forms are mainly used for cosmetics--the specified code is not enclosed inside
a block scope when it is emitted.   This sometimes results in a less complicated looking wrapper function.
Note that only the third of the three typemaps have the typemap code passed through the SWIG preprocessor.
</p>

<H3><a name="Typemaps_nn23"></a>11.4.2 Declaring new local variables</H3>


<p>
Sometimes it is useful to declare a new local variable that exists
within the scope of the entire wrapper function.  A good example of this
might be an application in which you wanted to marshal strings.   Suppose
you had a C++ function like this
</p>

<div class="code">
<pre>
int foo(std::string *s);
</pre>
</div>

<p>
and you wanted to pass a native string in the target language as an argument.   For instance,
in Perl, you wanted the function to work like this:
</p>

<div class="targetlang">
<pre>
$x = foo("Hello World");
</pre>
</div>

<p>
To do this, you can't just pass a raw Perl string as the <tt>std::string *</tt> argument. 
Instead, you have to create a temporary <tt>std::string</tt> object, copy the Perl string data into it, and
then pass a pointer to the object.   To do this, simply specify the typemap with an extra parameter like this:
</p>

<div class="code">
<pre>
%typemap(in) std::string * <b>(std::string temp)</b> {
    unsigned int len;
    char        *s;
    s = SvPV($input,len);         /* Extract string data */
    temp.assign(s,len);           /* Assign to temp */
    $1 = &amp;temp;                   /* Set argument to point to temp */
}
</pre>
</div>

<p>
In this case, <tt>temp</tt> becomes a local variable in
the scope of the entire wrapper function.  For example:
</p>

<div class="code">
<pre>
wrap_foo() {
   std::string temp;    &lt;--- Declaration of temp goes here
   ...

   /* Typemap code */
   {
      ...
      temp.assign(s,len);
      ...
   } 
   ...
}
</pre>
</div>

<p>
When you set <tt>temp</tt> to a value, it
persists for the duration of the wrapper function and gets
cleaned up automatically on exit. 
</p>

<p>
It is perfectly safe to use more than one typemap involving local
variables in the same declaration. For example, you could declare a
function as :</p>

<div class="code"><pre>
void foo(std::string *x, std::string *y, std::string *z);
</pre></div>

<p>
This is safely handled because SWIG actually renames all local
variable references by appending an argument number suffix.  Therefore, the
generated code would actually look like this:
</p>

<div class="code">
<pre>
wrap_foo() {
   int *arg1;    /* Actual arguments */
   int *arg2;
   int *arg3;
   std::string temp1;    /* Locals declared in the typemap */
   std::string temp2;
   std::string temp3;
   ...
   {
       char *s;
       unsigned int len;
       ...
       temp1.assign(s,len);
       arg1 = *temp1;
   }
   {
       char *s;
       unsigned int len;
       ...
       temp2.assign(s,len);
       arg2 = &amp;temp2;
   }
   {
       char *s;
       unsigned int len;
       ...
       temp3.assign(s,len);
       arg3 = &amp;temp3;
   }
   ...
}
</pre>
</div>

<p>
Some typemaps do not recognize local variables (or they may simply not
apply). At this time, only typemaps that apply to argument conversion support this (input typemaps such as the "in" typemap).
</p>

<p>
<b>Note:</b>
</p>

<p>
When declaring a typemap for multiple types, 
each type must have its own local variable declaration.
</p>

<div class="code">
<pre>
%typemap(in) const std::string *, std::string * (std::string temp) // NO!
// only std::string * has a local variable
// const std::string * does not (oops)
....

%typemap(in) const std::string * (std::string temp), std::string * (std::string temp) // Correct
....
</pre>
</div>


<H3><a name="Typemaps_special_variables"></a>11.4.3 Special variables</H3>


<p>
Within all typemaps, the following special variables are expanded.
This is by no means a complete list as some target languages have additional special variables which are documented in the language specific chapters.
</p>

<center>
<table border=1 summary="Typemap special variables">
<tr><th>Variable</th><th>Meaning</th></tr>

<tr>
<td>$<em>n</em></td>
<td>
A C local variable corresponding to type <em>n</em> in the typemap
pattern.
</td>
</tr>

<tr>
<td>$argnum</td>
<td>Argument number.  Only available in typemaps related to argument conversion</td>
</tr>

<tr>
<td>$<em>n</em>_name</td>
<td>Argument name</td>
</tr>

<tr>
<td>$<em>n</em>_type</td>
<td>Real C datatype of type <em>n</em>.</td>
</tr>

<tr>
<td>$<em>n</em>_ltype</td>
<td>ltype of type <em>n</em></td>
</tr>

<tr>
<td>$<em>n</em>_mangle</td>
<td>Mangled form of type <em>n</em>.  For example <tt>_p_Foo</tt></td>
</tr>

<tr>
<td>$<em>n</em>_descriptor</td>
<td>Type descriptor structure for type <em>n</em>.  For example
<tt>SWIGTYPE_p_Foo</tt>.  This is primarily used when interacting with the
run-time type checker (described later).</td>
</tr>


<tr>
<td>$*<em>n</em>_type</td>
<td>Real C datatype of type <em>n</em> with one pointer removed.</td>
</tr>

<tr>
<td>$*<em>n</em>_ltype</td>
<td>ltype of type <em>n</em> with one pointer removed.</td>
</tr>

<tr>
<td>$*<em>n</em>_mangle</td>
<td>Mangled form of type <em>n</em> with one pointer removed. </td>
</tr>

<tr>
<td>$*<em>n</em>_descriptor</td>
<td>Type descriptor structure for type <em>n</em> with one pointer removed.
</tr>


<tr>
<td>$&amp;<em>n</em>_type</td>
<td>Real C datatype of type <em>n</em> with one pointer added.</td>
</tr>

<tr>
<td>$&amp;<em>n</em>_ltype</td>
<td>ltype of type <em>n</em> with one pointer added.</td>
</tr>

<tr>
<td>$&amp;<em>n</em>_mangle</td>
<td>Mangled form of type <em>n</em> with one pointer added.</td>
</tr>

<tr>
<td>$&amp;<em>n</em>_descriptor</td>
<td>Type descriptor structure for type <em>n</em> with one pointer added.
</tr>

<tr>
<td>$<em>n</em>_basetype</td>
<td>Base typename with all pointers and qualifiers stripped.
</td>
</tr>

</table>
</center>

<p>
Within the table, $<em>n</em> refers to a specific type within the typemap specification.  For example,
if you write this
</p>

<div class="code">
<pre>
%typemap(in) int *INPUT {

}
</pre>
</div>

<p>
then $1 refers to <tt>int *INPUT</tt>.  If you have a typemap like this,
</p>

<div class="code">
<pre>
%typemap(in) (int argc, char *argv[]) {
  ...
}
</pre>
</div>

<p>
then $1 refers to <tt>int argc</tt> and $2 refers to <tt>char *argv[]</tt>.
</p>

<p>
Substitutions related to types and names always fill in values from the actual code that was matched.
This is useful when a typemap might match multiple C datatype.  For example:
</p>

<div class="code">
<pre>
%typemap(in)  int, short, long {
   $1 = ($1_ltype) PyInt_AsLong($input);
}
</pre>
</div>

<p>
In this case, <tt>$1_ltype</tt> is replaced with the datatype that is actually matched.
</p>


<p>
When typemap code is emitted, the C/C++ datatype of the special variables <tt>$1</tt> and 
<tt>$2</tt> is always an "ltype."   An "ltype" is simply a type that can legally appear
on the left-hand side of a C assignment operation.   Here are a few examples of types
and ltypes:
</p>

<div class="diagram">
<pre>
type              ltype
------            ----------------
int               int
const int         int
const int *       int *
int [4]           int *
int [4][5]        int (*)[5]
</pre>
</div>

<p>
In most cases a ltype is simply the C datatype with qualifiers stripped off.  In addition,
arrays are converted into pointers.
</p>

<p>
Variables such as <tt>$&amp;1_type</tt> and <tt>$*1_type</tt> are used to
safely modify the type by removing or adding pointers.  Although not
needed in most typemaps, these substitutions are sometimes needed to properly
work with typemaps that convert values between pointers and values.  
</p>

<p>
If necessary, type related substitutions can also be used when declaring locals.  For example:
</p>

<div class="code">
<pre>
%typemap(in) int * ($*1_type temp) {
    temp = PyInt_AsLong($input);
    $1 = &amp;temp;
}
</pre>
</div>

<p>
There is one word of caution about declaring local variables in this manner. If you declare a local variable
using a type substitution such as <tt>$1_ltype temp</tt>, it won't work like you expect for arrays and certain
kinds of pointers.   For example, if you wrote this,
</p>

<div class="code">
<pre>
%typemap(in) int [10][20] {
   $1_ltype temp;
}
</pre>
</div>

<p>
then the declaration of <tt>temp</tt> will be expanded as 
</p>

<div class="code">
<pre>
int (*)[20] temp;
</pre>
</div>

<p>
This is illegal C syntax and won't compile.  There is currently no
straightforward way to work around this problem in SWIG due to the way
that typemap code is expanded and processed.  However, one possible workaround
is to simply pick an alternative type such as <tt>void *</tt> and use
casts to get the correct type when needed.  For example:
</p>

<div class="code">
<pre>
%typemap(in) int [10][20] {
   void *temp;
   ...
   (($1_ltype) temp)[i][j] = x;    /* set a value */
   ...
}
</pre>
</div>

<p>
Another approach, which only works for arrays is to use the <tt>$1_basetype</tt> substitution.  For example:
</p>

<div class="code">
<pre>
%typemap(in) int [10][20] {
   $1_basetype temp[10][20];
   ...
   temp[i][j] = x;    /* set a value */
   ...
}
</pre>
</div>

<H3><a name="Typemaps_special_variable_macros"></a>11.4.4 Special variable macros</H3>


<p>
Special variable macros are like macro functions in that they take one or more input arguments 
which are used for the macro expansion. 
They look like macro/function calls but use the special variable <tt>$</tt> prefix to the macro name. 
Note that unlike normal macros, the expansion is not done by the preprocessor, 
it is done during the SWIG parsing/compilation stages. 
The following special variable macros are available across all language modules.
</p>

<H4><a name="Typemaps_special_macro_descriptor"></a>11.4.4.1 $descriptor(type)</H4>


<p>
This macro expands into the type descriptor structure for any C/C++ type specified in <tt>type</tt>.
It behaves like the <tt>$1_descriptor</tt> special variable described above except that the type to expand is 
taken from the macro argument rather than inferred from the typemap type. 
For example, <tt>$descriptor(std::vector&lt;int&gt; *)</tt> will expand into <tt>SWIGTYPE_p_std__vectorT_int_t</tt>.
This macro is mostly used in the scripting target languages and is demonstrated later in the <a href="#Typemaps_runtime_type_checker_usage">Run-time type checker usage</a> section.
</p>

<H4><a name="Typemaps_special_macro_typemap"></a>11.4.4.2 $typemap(method, typepattern)</H4>


<p>
This macro uses the <a href="#Typemaps_pattern_matching">pattern matching rules</a> described earlier to lookup and 
then substitute the special variable macro with the code in the matched typemap.
The typemap to search for is specified by the arguments, where <tt>method</tt> is the typemap method name and 
<tt>typepattern</tt> is a type pattern as per the <tt>%typemap</tt> specification in the <a href="#Typemaps_defining">Defining a typemap</a> section.
</p>

<p>
The special variables within the matched typemap are expanded into those for the matched typemap type, 
not the typemap within which the macro is called.
In practice, there is little use for this macro in the scripting target languages.
It is mostly used in the target languages that are statically typed as a way to obtain the target language type given the C/C++ type and more commonly only when the C++ type is a template parameter.
</p>

<p>
The example below is for C# only and uses some typemap method names documented in the C# chapter, but it shows some of the possible syntax variations.
</p>

<div class="code">
<pre>
%typemap(cstype) unsigned long    "uint"
%typemap(cstype) unsigned long bb "bool"
%typemap(cscode) BarClass %{
  void foo($typemap(cstype, unsigned long aa) var1,
           $typemap(cstype, unsigned long bb) var2,
           $typemap(cstype, (unsigned long bb)) var3,
           $typemap(cstype, unsigned long) var4)
  {
    // do something
  }
%}
</pre>
</div>

<p>
The result is the following expansion
</p>

<div class="code">
<pre>
%typemap(cstype) unsigned long    "uint"
%typemap(cstype) unsigned long bb "bool"
%typemap(cscode) BarClass %{
  void foo(uint var1,
           bool var2,
           bool var3,
           uint var4)
  {
    // do something
  }
%}
</pre>
</div>

<H2><a name="Typemaps_nn25"></a>11.5 Common typemap methods</H2>


<p>
The set of typemaps recognized by a language module may vary.  However,
the following typemap methods are nearly universal:
</p>

<H3><a name="Typemaps_nn26"></a>11.5.1 "in" typemap</H3>


<p>
The "in" typemap is used to convert function arguments from the target language
to C.  For example:
</p>

<div class="code">
<pre>
%typemap(in) int {
   $1 = PyInt_AsLong($input);
}
</pre>
</div>

<p>
The following special variables are available:
</p>

<div class="code">
<pre>
$input            - Input object holding value to be converted.
$symname          - Name of function/method being wrapped
</pre>
</div>

<p>
This is probably the most commonly redefined typemap because it can be used
to implement customized conversions.
</p>

<p>
In addition, the "in" typemap allows the number of converted arguments to be
specified.  The <tt>numinputs</tt> attributes facilitates this. For example:
</p>

<div class="code">
<pre>
// Ignored argument.
%typemap(in, numinputs=0) int *out (int temp) {
    $1 = &amp;temp;
}
</pre>
</div>

<p>
At this time, only zero or one arguments may be converted. 
When <tt>numinputs</tt> is set to 0, the argument is effectively ignored and cannot be supplied from the target language. 
The argument is still required when making the C/C++ call and the above typemap
shows the value used is instead obtained from a locally declared variable called <tt>temp</tt>.
Usually <tt>numinputs</tt> is not specified, whereupon the default value is 1, that is, there is a one to one mapping of the number of arguments when used from the target language to the C/C++ call. 
<a href="#Typemaps_multi_argument_typemaps">Multi-argument typemaps</a> provide a similar concept where the number of arguments mapped from the target language to C/C++ can be changed for multiple adjacent C/C++ arguments.
</p>

<p>
<b>Compatibility note: </b> Specifying <tt>numinputs=0</tt>
is the same as the old "ignore" typemap.
</p>

<H3><a name="Typemaps_nn27"></a>11.5.2 "typecheck" typemap</H3>


<p>
The "typecheck" typemap is used to support overloaded functions and methods.  It merely checks an argument
to see whether or not it matches a specific type.  For example:
</p>

<div class="code">
<pre>
%typemap(typecheck,precedence=SWIG_TYPECHECK_INTEGER) int {
   $1 = PyInt_Check($input) ? 1 : 0;
}
</pre>
</div>

<p>
For typechecking, the $1 variable is always a simple integer that is set to 1 or 0 depending on whether or not
the input argument is the correct type.
</p>

<p>
If you define new "in" typemaps <em>and</em> your program uses overloaded methods, you should also define a collection of
"typecheck" typemaps.  More details about this follow in the <a href="#Typemaps_overloading">Typemaps and overloading</a> section.
</p>

<H3><a name="Typemaps_nn28"></a>11.5.3 "out" typemap</H3>


<p>
The "out" typemap is used to convert function/method return values from C
into the target language.  For example:
</p>

<div class="code">
<pre>
%typemap(out) int {
   $result = PyInt_FromLong($1);
}
</pre>
</div>

<p>
The following special variables are available.
</p>

<div class="code">
<pre>
$result           - Result object returned to target language.
$symname          - Name of function/method being wrapped
</pre>
</div>

<p>
The "out" typemap supports an optional attribute flag called "optimal". This is for code optimisation and is detailed in the <a href="#Typemaps_optimal">Optimal code generation when returning by value</a> section.
</p>

<H3><a name="Typemaps_nn29"></a>11.5.4 "arginit" typemap</H3>


<p>
The "arginit" typemap is used to set the initial value of a function
argument--before any conversion has occurred.   This is not normally
necessary, but might be useful in highly specialized applications.
For example:
</p>

<div class="code">
<pre>
// Set argument to NULL before any conversion occurs
%typemap(arginit) int *data {
   $1 = NULL;
}
</pre>
</div>

<H3><a name="Typemaps_nn30"></a>11.5.5 "default" typemap</H3>


<p>
The "default" typemap is used to turn an argument into a default
argument.   For example:
</p>

<div class="code">
<pre>
%typemap(default) int flags {
   $1 = DEFAULT_FLAGS;
}
...
int foo(int x, int y, int flags);
</pre>
</div>

<p>
The primary use of this typemap is to either change the wrapping of
default arguments or specify a default argument in a language where
they aren't supported (like C). Target languages that do not support
optional arguments, such as Java and C#, effectively ignore the value specified
by this typemap as all arguments must be given.
</p>

<p>
Once a default typemap has been applied to an argument, all arguments
that follow must have default values.
See the <a href="SWIG.html#SWIG_default_args">Default/optional arguments</a> section
for further information on default argument wrapping.
</p>

<H3><a name="Typemaps_nn31"></a>11.5.6 "check" typemap</H3>


<p>
The "check" typemap is used to supply value checking code during argument
conversion.  The typemap is applied <em>after</em> arguments have been
converted.  For example:
</p>

<div class="code">
<pre>
%typemap(check) int positive {
   if ($1 &lt;= 0) {
       SWIG_exception(SWIG_ValueError,"Expected positive value.");
   }
}
</pre>
</div>

<H3><a name="Typemaps_nn32"></a>11.5.7 "argout" typemap</H3>


<p>
The "argout" typemap is used to return values from arguments.  This
is most commonly used to write wrappers for C/C++ functions that need
to return multiple values.   The "argout" typemap is almost always combined
with an "in" typemap---possibly to ignore the input value.  For example:
</p>

<div class="code">
<pre>
/* Set the input argument to point to a temporary variable */
%typemap(in, numinputs=0) int *out (int temp) {
   $1 = &amp;temp;
}

%typemap(argout) int *out {
   // Append output value $1 to $result
   ...
}
</pre>
</div>

<p>
The following special variables are available.
</p>

<div class="diagram">
<pre>
$result           - Result object returned to target language.
$input            - The original input object passed.
$symname          - Name of function/method being wrapped
</pre>
</div>

<p>
The code supplied to the "argout" typemap is always placed after
the "out" typemap.  If multiple return values are used, the extra
return values are often appended to return value of the function.
</p>

<p>
See the <tt>typemaps.i</tt> library file for examples.
</p>

<H3><a name="Typemaps_nn33"></a>11.5.8 "freearg" typemap</H3>


<p>
The "freearg" typemap is used to cleanup argument data.  It is only
used when an argument might have allocated resources that need to be
cleaned up when the wrapper function exits.  The "freearg" typemap
usually cleans up argument resources allocated by the "in" typemap.  
For example:
</p>

<div class="code">
<pre>
// Get a list of integers
%typemap(in) int *items {
   int nitems = Length($input);    
   $1 = (int *) malloc(sizeof(int)*nitems);
}
// Free the list 
%typemap(freearg) int *items {
   free($1);
}
</pre>
</div>

<p>
The "freearg" typemap inserted at the end of the wrapper function,
just before control is returned back to the target language.  This
code is also placed into a special variable <tt>$cleanup</tt> that may
be used in other typemaps whenever a wrapper function needs to abort
prematurely.
</p>

<H3><a name="Typemaps_nn34"></a>11.5.9 "newfree" typemap</H3>


<p>
The "newfree" typemap is used in conjunction with the <tt>%newobject</tt>
directive and is used to deallocate memory used by the return result 
of a function.  For example:
</p>

<div class="code">
<pre>
%typemap(newfree) string * {
   delete $1;
}
%typemap(out) string * {
   $result = PyString_FromString($1-&gt;c_str());
}
...

%newobject foo;
...
string *foo();
</pre>
</div>

<p>
See <a href="Customization.html#Customization_ownership">Object ownership and %newobject</a> for further details.
</p>

<H3><a name="Typemaps_nn35"></a>11.5.10 "memberin" typemap</H3>


<p>
The "memberin" typemap is used to copy data from <em>an already converted input value</em>
into a structure member.  It is typically used to handle array members and other special
cases.  For example:
</p>

<div class="code">
<pre>
%typemap(memberin) int [4] {
   memmove($1, $input, 4*sizeof(int));
}
</pre>
</div>

<p>
It is rarely necessary to write "memberin" typemaps---SWIG already provides
a default implementation for arrays, strings, and other objects.
</p>

<H3><a name="Typemaps_nn36"></a>11.5.11 "varin" typemap</H3>


<p>
The "varin" typemap is used to convert objects in the target language to C for the
purposes of assigning to a C/C++ global variable.    This is implementation specific.
</p>

<H3><a name="Typemaps_nn37"></a>11.5.12 "varout" typemap</H3>


<p>
The "varout" typemap is used to convert a C/C++ object to an object in the target
language when reading a C/C++ global variable.  This is implementation specific.
</p>

<H3><a name="throws_typemap"></a>11.5.13 "throws" typemap</H3>


<p>
The "throws" typemap is only used when SWIG parses a C++ method with an exception specification or has the <tt>%catches</tt> feature attached to the method.
It provides a default mechanism for handling C++ methods that have declared the exceptions they will throw.
The purpose of this typemap is to convert a C++ exception into an error or exception in the target language.
It is slightly different to the other typemaps as it is based around the exception type rather than the type of a parameter or variable.
For example:
</p>

<div class="code">
<pre>
%typemap(throws) const char * %{
  PyErr_SetString(PyExc_RuntimeError, $1);
  SWIG_fail;
%}
void bar() throw (const char *);
</pre>
</div>

<p>
As can be seen from the generated code below, SWIG generates an exception handler
with the catch block comprising the "throws" typemap content.
</p>

<div class="code">
<pre>
...
try {
    bar();
}
catch(char const *_e) {
    PyErr_SetString(PyExc_RuntimeError, _e);
    SWIG_fail;
    
}
...
</pre>
</div>

<p>
Note that if your methods do not have an exception specification yet they do throw exceptions, SWIG cannot know how to deal with them.
For a neat way to handle these, see the <a href="Customization.html#Customization_exception">Exception handling with %exception</a> section.
</p>

<H2><a name="Typemaps_nn39"></a>11.6 Some typemap examples</H2>


<p>
This section contains a few examples.  Consult language module documentation
for more examples.
</p>

<H3><a name="Typemaps_nn40"></a>11.6.1 Typemaps for arrays</H3>


<p>
A common use of typemaps is to provide support for C arrays appearing both as
arguments to functions and as structure members.
</p>

<p>
For example, suppose you had a function like this:
</p>

<div class="code">
<pre>
void set_vector(int type, float value[4]);
</pre>
</div>

<p>
If you wanted to handle <tt>float value[4]</tt> as a list of floats, you might write a typemap
similar to this:
</p>

<div class="code">
<pre>

%typemap(in) float value[4] (float temp[4]) {
  int i;
  if (!PySequence_Check($input)) {
    PyErr_SetString(PyExc_ValueError,"Expected a sequence");
    return NULL;
  }
  if (PySequence_Length($input) != 4) {
    PyErr_SetString(PyExc_ValueError,"Size mismatch. Expected 4 elements");
    return NULL;
  }
  for (i = 0; i &lt; 4; i++) {
    PyObject *o = PySequence_GetItem($input,i);
    if (PyNumber_Check(o)) {
      temp[i] = (float) PyFloat_AsDouble(o);
    } else {
      PyErr_SetString(PyExc_ValueError,"Sequence elements must be numbers");      
      return NULL;
    }
  }
  $1 = temp;
}
</pre>
</div>

<p>
In this example, the variable <tt>temp</tt> allocates a small array on the
C stack.  The typemap then populates this array and passes it to the underlying C function.
</p>

<p>
When used from Python, the typemap allows the following type of function call:
</p>

<div class="targetlang">
<pre>
&gt;&gt;&gt; set_vector(type, [ 1, 2.5, 5, 20 ])
</pre>
</div>

<p>
If you wanted to generalize the typemap to apply to arrays of all dimensions you might write this:
</p>

<div class="code">
<pre>
%typemap(in) float value[ANY] (float temp[$1_dim0]) {
  int i;
  if (!PySequence_Check($input)) {
    PyErr_SetString(PyExc_ValueError,"Expected a sequence");
    return NULL;
  }
  if (PySequence_Length($input) != $1_dim0) {
    PyErr_SetString(PyExc_ValueError,"Size mismatch. Expected $1_dim0 elements");
    return NULL;
  }
  for (i = 0; i &lt; $1_dim0; i++) {
    PyObject *o = PySequence_GetItem($input,i);
    if (PyNumber_Check(o)) {
      temp[i] = (float) PyFloat_AsDouble(o);
    } else {
      PyErr_SetString(PyExc_ValueError,"Sequence elements must be numbers");      
      return NULL;
    }
  }
  $1 = temp;
}
</pre>
</div>

<p>
In this example, the special variable <tt>$1_dim0</tt> is expanded with the actual
array dimensions.   Multidimensional arrays can be matched in a similar manner.  For example:
</p>

<div class="code">
<pre>
%typemap(in) float matrix[ANY][ANY] (float temp[$1_dim0][$1_dim1]) {
   ... convert a 2d array ...
}
</pre>
</div>

<p>
For large arrays, it may be impractical to allocate storage on the stack using a temporary variable
as shown.   To work with heap allocated data, the following technique can be used.
</p>

<div class="code">
<pre>
%typemap(in) float value[ANY] {
  int i;
  if (!PySequence_Check($input)) {
    PyErr_SetString(PyExc_ValueError,"Expected a sequence");
    return NULL;
  }
  if (PySequence_Length($input) != $1_dim0) {
    PyErr_SetString(PyExc_ValueError,"Size mismatch. Expected $1_dim0 elements");
    return NULL;
  }
  $1 = (float *) malloc($1_dim0*sizeof(float));
  for (i = 0; i &lt; $1_dim0; i++) {
    PyObject *o = PySequence_GetItem($input,i);
    if (PyNumber_Check(o)) {
      $1[i] = (float) PyFloat_AsDouble(o);
    } else {
      PyErr_SetString(PyExc_ValueError,"Sequence elements must be numbers");      
      free($1);
      return NULL;
    }
  }
}
%typemap(freearg) float value[ANY] {
   if ($1) free($1);
}
</pre>
</div>

<p>
In this case, an array is allocated using <tt>malloc</tt>.   The <tt>freearg</tt> typemap is then used
to release the argument after the function has been called.
</p>

<p>
Another common use of array typemaps is to provide support for array structure members.
Due to subtle differences between pointers and arrays in C, you can't just "assign" to
a array structure member.  Instead, you have to explicitly copy elements into the array.
For example, suppose you had a structure like this:
</p>

<div class="code"><pre>
struct SomeObject {
	float  value[4];
        ...
};
</pre></div>

<p>
When SWIG runs, it won't produce any code to set the <tt>vec</tt> member.
You may even get a warning message like this:
</p>

<div class="shell"><pre>
$ swig -python  example.i
example.i:10: Warning 462: Unable to set variable of type float [4].
</pre></div>

<p>
These warning messages indicate that SWIG does not know how you want
to set the <tt>vec</tt> field.
</p>

<p>
To fix this, you can supply a special "memberin" typemap like this:
</p>

<div class="code"><pre>
%typemap(memberin) float [ANY] {
  int i;
  for (i = 0; i &lt; $1_dim0; i++) {
      $1[i] = $input[i];
  }
}
</pre></div>

<p>
The memberin typemap is used to set a structure member from data that has already been converted
from the target language to C.  In this case, <tt>$input</tt> is the local variable in which 
converted input data is stored.   This typemap then copies this data into the structure. 
</p>

<p>
When combined with the earlier typemaps for arrays, the combination of the "in" and "memberin" typemap allows
the following usage:
</p>

<div class="targetlang">
<pre>
&gt;&gt;&gt; s = SomeObject()
&gt;&gt;&gt; s.x = [1, 2.5, 5, 10]
</pre>
</div>

<p>
Related to structure member input, it may be desirable to return structure members as a new kind of
object.  For example, in this example, you will get very odd program behavior where the structure member
can be set nicely, but reading the member simply returns a pointer:
</p>

<div class="targetlang">
<pre>
&gt;&gt;&gt; s = SomeObject()
&gt;&gt;&gt; s.x = [1, 2.5, 5, 10]
&gt;&gt;&gt; print s.x
_1008fea8_p_float
&gt;&gt;&gt; 
</pre>
</div>

<p>
To fix this, you can write an "out" typemap.   For example:
</p>

<div class="code">
<pre>
%typemap(out) float [ANY] {
  int i;
  $result = PyList_New($1_dim0);
  for (i = 0; i &lt; $1_dim0; i++) {
    PyObject *o = PyFloat_FromDouble((double) $1[i]);
    PyList_SetItem($result,i,o);
  }
}
</pre>
</div>

<p>
Now, you will find that member access is quite nice:
</p>

<div class="targetlang">
<pre>
&gt;&gt;&gt; s = SomeObject()
&gt;&gt;&gt; s.x = [1, 2.5, 5, 10]
&gt;&gt;&gt; print s.x
[ 1, 2.5, 5, 10]
</pre>
</div>

<p>
<b>Compatibility Note:</b>  SWIG1.1 used to provide a special "memberout" typemap.  However, it was mostly
useless and has since been eliminated.   To return structure members, simply use the "out" typemap.
</p>

<H3><a name="Typemaps_nn41"></a>11.6.2 Implementing constraints with typemaps</H3>


<p>
One particularly interesting application of typemaps is the
implementation of argument constraints. This can be done with the
"check" typemap. When used, this allows you to provide code for
checking the values of function arguments. For example:</p>

<div class="code"><pre>
%module math

%typemap(check) double posdouble {
	if ($1 &lt; 0) {
		croak("Expecting a positive number");
	}
}

...
double sqrt(double posdouble);

</pre></div>

<p>
This provides a sanity check to your wrapper function. If a negative
number is passed to this function, a Perl exception will be raised and
your program terminated with an error message.</p>

<p>
This kind of checking can be particularly useful when working with
pointers. For example:</p>

<div class="code"><pre>
%typemap(check) Vector * {
    if ($1 == 0) {
        PyErr_SetString(PyExc_TypeError,"NULL Pointer not allowed");
        return NULL;
   }
}

</pre></div>

<p>
will prevent any function involving a <tt>Vector *</tt> from accepting
a NULL pointer. As a result, SWIG can often prevent a potential
segmentation faults or other run-time problems by raising an exception
rather than blindly passing values to the underlying C/C++ program.</p>

<H2><a name="Typemaps_nn43"></a>11.7 Typemaps for multiple target languages</H2>


<p>
The code within typemaps is usually language dependent,
however, many target languages support the same typemaps.
In order to distinguish typemaps across different languages, the preprocessor should be used.
For example, the "in" typemap for Perl and Ruby could be written as:
</p>

<div class="code"><pre>
#if defined(SWIGPERL)
  %typemap(in) int "$1 = ($1_ltype) SvIV($input);"
#elif defined(SWIGRUBY)
  %typemap(in) int "$1 = NUM2INT($input);"
#else
  #warning no "in" typemap defined
#endif
</pre></div>

<p>
The full set of language specific macros is defined in the <a href="Preprocessor.html#Preprocessor_condition_compilation">Conditional Compilation</a> section.
The example above also shows a common approach of issuing a warning for an as yet unsupported language.
</p>

<p>
<b>Compatibility note: </b> In SWIG-1.1 different languages could be distinguished with the language name being put within the <tt>%typemap</tt> directive, for example, <br>
<tt>%typemap(ruby,in) int "$1 = NUM2INT($input);"</tt>.
</p>

<H2><a name="Typemaps_optimal"></a>11.8 Optimal code generation when returning by value</H2>


<p>
The "out" typemap is the main typemap for return types.
This typemap supports an optional attribute flag called "optimal", which is for reducing 
temporary variables and the amount of generated code, thereby giving the compiler the opportunity to 
use <i>return value optimization</i> for generating faster executing code.
It only really makes a difference when returning objects by value and has some limitations on usage,
as explained later on.
</p>

<p>
When a function returns an object by value, SWIG generates code that instantiates the default
type on the stack then assigns the value returned by the function call to it.
A copy of this object is then made on the heap and this is what is ultimately stored and
used from the target language.
This will be clearer considering an example.
Consider running the following code through SWIG:
</p>

<div class="code">
<pre>
%typemap(out) SWIGTYPE %{
  $result = new $1_ltype((const $1_ltype &amp;)$1);
%}

%inline %{
#include &lt;iostream&gt;
using namespace std;

struct XX {
  XX() { cout &lt;&lt; "XX()" &lt;&lt; endl; }
  XX(int i) { cout &lt;&lt; "XX(" &lt;&lt; i &lt;&lt; ")" &lt;&lt; endl; }
  XX(const XX &amp;other) { cout &lt;&lt; "XX(const XX &amp;)" &lt;&lt; endl; }
  XX &amp; operator =(const XX &amp;other) { cout &lt;&lt; "operator=(const XX &amp;)" &lt;&lt; endl; return *this; }
  ~XX() { cout &lt;&lt; "~XX()" &lt;&lt; endl; }
  static XX create() { 
    return XX(0);
  }
};
%}
</pre>
</div>

<p>
The "out" typemap shown is the default typemap for C# when returning objects by value.
When making a call to <tt>XX::create()</tt> from C#, the output is as follows:
</p>

<div class="targetlang">
<pre>
XX()
XX(0)
operator=(const XX &amp;)
~XX()
XX(const XX &amp;)
~XX()
~XX()
</pre>
</div>

<p>
Note that three objects are being created as well as an assignment.
Wouldn't it be great if the <tt>XX::create()</tt> method was the only time a constructor was called?
As the method returns by value, this is asking a lot and the code that SWIG generates by default
makes it impossible for the compiler to use <i>return value optimisation (RVO)</i>.
However, this is where the "optimal" attribute in the "out" typemap can help out.
If the typemap code is kept the same and just the "optimal" attribute specified like this:
</p>

<div class="code">
<pre>
%typemap(out, optimal="1") SWIGTYPE %{
  $result = new $1_ltype((const $1_ltype &amp;)$1);
%}
</pre>
</div>

<p>
then when the code is run again, the output is simply:
</P>

<div class="targetlang">
<pre>
XX(0)
~XX()
</pre>
</div>

<p>
How the "optimal" attribute works is best explained using the generated code.
Without "optimal", the generated code is:
</p>

<div class="code">
<pre>
SWIGEXPORT void * SWIGSTDCALL CSharp_XX_create() {
  void * jresult ;
  XX result;
  result = XX::create();
  jresult = new XX((const XX &amp;)result);
  return jresult;
}

</pre>
</div>

<p>
With the "optimal" attribute, the code is:
</p>

<div class="code">
<pre>
SWIGEXPORT void * SWIGSTDCALL CSharp_XX_create() {
  void * jresult ;
  jresult = new XX((const XX &amp;)XX::create());
  return jresult;
}
</pre>
</div>

<p>
The major difference is the <tt>result</tt> temporary variable holding the value returned from <tt>XX::create()</tt> is no longer generated and instead the copy constructor call is made directly from
the value returned by <tt>XX::create()</tt>.
With modern compilers implementing RVO, the copy is not actually done, in fact the object is never created
on the stack in <tt>XX::create()</tt> at all, it is simply created directly on the heap.
In the first instance, the <tt>$1</tt> special variable in the typemap is expanded into <tt>result</tt>.
In the second instance, <tt>$1</tt> is expanded into <tt>XX::create()</tt> and this is essentially
what the "optimal" attribute is telling SWIG to do.
</p>

<p>
The "optimal" attribute optimisation is not turned on by default as it has a number of restrictions.
Firstly, some code cannot be condensed into a simple call for passing into the copy constructor.
One common occurrence is when <a href="Customization.html#Customization_exception">%exception</a> is used.
Consider adding the following <tt>%exception</tt> to the example:
</p>

<div class="code">
<pre>
%exception XX::create() %{
try {
  $action
} catch(const std::exception &amp;e) {
  cout &lt;&lt; e.what() &lt;&lt; endl;
}
%}
</pre>
</div>

<p>
SWIG can detect when the "optimal" attribute cannot be used and will ignore it and in this case will issue the following warning:
</p>

<div class="targetlang">
<pre>
example.i:28: Warning 474: Method XX::create() usage of the optimal attribute ignored
example.i:14: Warning 474: in the out typemap as the following cannot be used to generate
optimal code: 
try {
  result = XX::create();
} catch(const std::exception &amp;e) {
  cout &lt;&lt; e.what() &lt;&lt; endl;
}
</pre>
</div>

<p>
It should be clear that the above code cannot be used as the argument to the copy constructor call, that is, for the <tt>$1</tt> substitution.
</p>

<p>
Secondly, if the typemaps uses <tt>$1</tt> more than once, then multiple calls to the wrapped function
will be made. Obviously that is not very optimal.
In fact SWIG attempts to detect this and will issue a warning something like:
</p>

<div class="targetlang">
<pre>
example.i:21: Warning 475: Multiple calls to XX::create() might be generated due to
example.i:7: Warning 475: optimal attribute usage in the out typemap.
</pre>
</div>

<p>
However, it doesn't always get it right, for example when <tt>$1</tt> is within some commented out code.
</p>

<H2><a name="Typemaps_multi_argument_typemaps"></a>11.9 Multi-argument typemaps</H2>


<p>
So far, the typemaps presented have focused on the problem of dealing with
single values.  For example, converting a single input object to a single argument
in a function call.   However, certain conversion problems are difficult to handle
in this manner.   As an example, consider the example at the very beginning of this
chapter:
</p>

<div class="code">
<pre>
int foo(int argc, char *argv[]);
</pre>
</div>

<p>
Suppose that you wanted to wrap this function so that it accepted a single
list of strings like this:
</p>

<div class="targetlang">
<pre>
&gt;&gt;&gt; foo(["ale","lager","stout"])
</pre>
</div>

<p>
To do this, you not only need to map a list of strings to <tt> char *argv[]</tt>, but the
value of <tt>int argc</tt> is implicitly determined by the length of the list.   Using only simple
typemaps, this type of conversion is possible, but extremely painful.
Multi-argument typemaps help in this situation.
</p>

<p>
A multi-argument typemap is a conversion rule that specifies how to
convert a <em>single</em> object in the target language to a set of
consecutive function arguments in C/C++.  For example, the following multi-argument
maps perform the conversion described for the above example: 
</p>

<div class="code">
<pre>
%typemap(in) (int argc, char *argv[]) {
  int i;
  if (!PyList_Check($input)) {
    PyErr_SetString(PyExc_ValueError, "Expecting a list");
    return NULL;
  }
  $1 = PyList_Size($input);
  $2 = (char **) malloc(($1+1)*sizeof(char *));
  for (i = 0; i &lt; $1; i++) {
    PyObject *s = PyList_GetItem($input,i);
    if (!PyString_Check(s)) {
        free($2);
        PyErr_SetString(PyExc_ValueError, "List items must be strings");
        return NULL;
    }
    $2[i] = PyString_AsString(s);
  }
  $2[i] = 0;
}

%typemap(freearg) (int argc, char *argv[]) {
   if ($2) free($2);
}
</pre>
</div>

<p>
A multi-argument map is always specified by surrounding the arguments with parentheses as shown.
For example:
</p>

<div class="code">
<pre>
%typemap(in) (int argc, char *argv[]) { ... }
</pre>
</div>

<p>
Within the typemap code, the variables <tt>$1</tt>, <tt>$2</tt>, and so forth refer to each type
in the map.  All of the usual substitutions apply--just use the appropriate <tt>$1</tt> or <tt>$2</tt>
prefix on the variable name (e.g., <tt>$2_type</tt>, <tt>$1_ltype</tt>, etc.)
</p>

<p>
Multi-argument typemaps always have precedence over simple typemaps and SWIG always performs longest-match searching.
Therefore, you will get the following behavior:
</p>

<div class="code">
<pre>
%typemap(in) int argc                              { ... typemap 1 ... }
%typemap(in) (int argc, char *argv[])              { ... typemap 2 ... }
%typemap(in) (int argc, char *argv[], char *env[]) { ... typemap 3 ... }

int foo(int argc, char *argv[]);                   // Uses typemap 2
int bar(int argc, int x);                          // Uses typemap 1
int spam(int argc, char *argv[], char *env[]);     // Uses typemap 3
</pre>
</div>

<p>
It should be stressed that multi-argument typemaps can appear anywhere in a function declaration and can
appear more than once.  For example, you could write this:
</p>

<div class="code">
<pre>
%typemap(in) (int scount, char *swords[]) { ... }
%typemap(in) (int wcount, char *words[]) { ... }

void search_words(int scount, char *swords[], int wcount, char *words[], int maxcount);
</pre>
</div>

<p>
Other directives such as <tt>%apply</tt> and <tt>%clear</tt> also work with multi-argument maps.  For example:
</p>

<div class="code">
<pre>
%apply (int argc, char *argv[]) {
    (int scount, char *swords[]),
    (int wcount, char *words[])
};
...
%clear (int scount, char *swords[]), (int wcount, char *words[]);
...
</pre>
</div>

<p>
Although multi-argument typemaps may seem like an exotic, little used feature, there
are several situations where they make sense.  First, suppose you wanted to wrap
functions similar to the low-level <tt>read()</tt> and <tt>write()</tt> system calls.
For example:
</p>

<div class="code">
<pre>
typedef unsigned int size_t;

int read(int fd, void *rbuffer, size_t len);
int write(int fd, void *wbuffer, size_t len);
</pre>
</div>

<p>
As is, the only way to use the functions would be to allocate memory and pass some kind of pointer
as the second argument---a process that might require the use of a helper function.  However, using
multi-argument maps, the functions can be transformed into something more natural.  For example, you 
might write typemaps like this:
</p>

<div class="code">
<pre>
// typemap for an outgoing buffer
%typemap(in) (void *wbuffer, size_t len) {
   if (!PyString_Check($input)) {
       PyErr_SetString(PyExc_ValueError, "Expecting a string");
       return NULL;
   }
   $1 = (void *) PyString_AsString($input);
   $2 = PyString_Size($input);
}

// typemap for an incoming buffer
%typemap(in) (void *rbuffer, size_t len) {
   if (!PyInt_Check($input)) {
       PyErr_SetString(PyExc_ValueError, "Expecting an integer");
       return NULL;
   }
   $2 = PyInt_AsLong($input);
   if ($2 &lt; 0) {
       PyErr_SetString(PyExc_ValueError, "Positive integer expected");
       return NULL;
   }
   $1 = (void *) malloc($2);
}

// Return the buffer.  Discarding any previous return result
%typemap(argout) (void *rbuffer, size_t len) {
   Py_XDECREF($result);   /* Blow away any previous result */
   if (result &lt; 0) {      /* Check for I/O error */
       free($1);
       PyErr_SetFromErrno(PyExc_IOError);
       return NULL;
   }
   $result = PyString_FromStringAndSize($1,result);
   free($1);
}
</pre>
</div>

<p>
(note: In the above example, <tt>$result</tt> and <tt>result</tt> are two different variables.
<tt>result</tt> is the real C datatype that was returned by the function.  <tt>$result</tt> is the
scripting language object being returned to the interpreter.).
</p>

<p>
Now, in a script, you can write code that simply passes buffers as strings like this:
</p>

<div class="targetlang">
<pre>
&gt;&gt;&gt; f = example.open("Makefile")
&gt;&gt;&gt; example.read(f,40)
'TOP        = ../..\nSWIG       = $(TOP)/.'
&gt;&gt;&gt; example.read(f,40)
'./swig\nSRCS       = example.c\nTARGET    '
&gt;&gt;&gt; example.close(f)
0
&gt;&gt;&gt; g = example.open("foo", example.O_WRONLY | example.O_CREAT, 0644)
&gt;&gt;&gt; example.write(g,"Hello world\n")
12
&gt;&gt;&gt; example.write(g,"This is a test\n")
15
&gt;&gt;&gt; example.close(g)
0
&gt;&gt;&gt;
</pre>
</div>

<p>
A number of multi-argument typemap problems also arise in libraries that
perform matrix-calculations--especially if they are mapped onto low-level Fortran
or C code. For example, you might have a function like this:
</p>

<div class="code">
<pre>
int is_symmetric(double *mat, int rows, int columns);
</pre>
</div>

<p>
In this case, you might want to pass some kind of higher-level object as an matrix.  To do
this, you could write a multi-argument typemap like this:
</p>

<div class="code">
<pre>
%typemap(in) (double *mat, int rows, int columns) {
    MatrixObject *a;
    a = GetMatrixFromObject($input);     /* Get matrix somehow */

    /* Get matrix properties */
    $1 = GetPointer(a);
    $2 = GetRows(a);
    $3 = GetColumns(a);
}
</pre>
</div>

<p>
This kind of technique can be used to hook into scripting-language matrix packages such as
Numeric Python.  However, it should also be stressed that some care is in order.  For example,
when crossing languages you may need to worry about issues such as row-major vs. column-major
ordering (and perform conversions if needed). Note that multi-argument typemaps cannot deal
with non-consecutive C/C++ arguments; a workaround such as a helper function re-ordering
the arguments to make them consecutive will need to be written.
</p>

<H2><a name="Typemaps_warnings"></a>11.10 Typemap warnings</H2>


<p>
Warnings can be added to typemaps so that SWIG generates a warning message whenever the typemap is used.
See the information in the <a href="Warnings.html#Warnings_nn5">issuing warnings</a> section.
</p>


<H2><a name="Typemaps_fragments"></a>11.11 Typemap fragments</H2>


<p>
The primary purpose of fragments is to reduce code bloat that repeated use of typemap code can lead to.
Fragments are snippets of code that can be thought of as code dependencies of a typemap.
If a fragment is used by more than one typemap, then the snippet of code within the fragment is only generated once.
Code bloat is typically reduced by moving typemap code into a support function
and then placing the support function into a fragment.
</p>

<p>
For example, if you have a very long typemap
</p>

<div class="code">
<pre>
%typemap(in) MyClass * {
  MyClass *value = 0;

  ... many lines of marshalling code  ...

  $result = value;
}
</pre>
</div>

<p>
the same marshalling code is often repeated in several typemaps, such as "in", "varin", "directorout", etc.
SWIG copies the code for each argument that requires the typemap code, easily leading to code bloat
in the generated code.
To eliminate this, define a fragment that includes the common marshalling code:
</p>

<div class="code">
<pre>
%fragment("AsMyClass", "header") {
  MyClass *AsMyClass(PyObject *obj) {
    MyClass *value = 0;

    ... many lines of marshalling code  ...

    return value;
  }
}

%typemap(in, fragment="AsMyClass") MyClass * {
  $result = AsMyClass($input);
}

%typemap(varin, fragment="AsMyClass") MyClass * {
  $result = AsMyClass($input);
}
</pre>
</div>

<p>
When the "in" or "varin" typemaps for MyClass are required, the
contents of the fragment called "AsMyClass" is added to the "header" section within the generated code, and then the
typemap code is emitted. Hence, the method <tt>AsMyClass</tt> will be
generated into the wrapper code before any typemap code that calls it.
</p>

<p>
To define a fragment you need a fragment name, a section name for generating the fragment code into, and the code itself.
See <a href="SWIG.html#SWIG_nn42">Code insertion blocks</a> for a full list of section names.
Usually the section name used is "header". Different delimiters can be used:
</p>

<div class="code">
<pre>
%fragment("my_name", "header") %{ ... %}
%fragment("my_name", "header") { ... }
%fragment("my_name", "header") " ... "
</pre>
</div>

<p>
and these follow the usual preprocessing rules mentioned in the 
<a href="Preprocessor.html#Preprocessor_delimiters">Preprocessing delimiters</a>
section.
The following are some rules and guidelines for using fragments:
</p>

<ol>
<li>
<p>
A fragment is added to the wrapping code only once. When using the <tt>MyClass *</tt> typemaps above and wrapping the method:
</p>

<div class="code">
<pre>
void foo(MyClass *a, MyClass *b);
</pre>
</div>

<p>
the generated code will look something like:
</p>

<div class="code">
<pre>
MyClass *AsMyClass(PyObject *obj) {
  ...
}

void _wrap_foo(...) {
  ....
  arg1 = AsMyClass(obj1);
  arg2 = AsMyClass(obj2);
  ...
  foo(arg1, arg2);
}
</pre>
</div>

<p>
even as there is duplicated typemap code to process both <tt>a</tt> and
<tt>b</tt>, the <tt>AsMyClass</tt> method will be defined only once.
</p>

<li>
<p>
A fragment should only be defined once. If there is more than
one definition, the first definition is the one used.
All other definitions are silently ignored. For example, if you have
</p>


<div class="code">
<pre>
%fragment("AsMyClass", "header") { ...definition 1... }
....
%fragment("AsMyClass", "header") { ...definition 2... }
</pre>
</div>

<p>
only the first definition is used. In this way
you can override the default fragments in a SWIG library by defining your fragment before the library <tt>%include</tt>.
Note that this behavior is the opposite to typemaps, where the last typemap defined/applied prevails.
Fragments follow the first-in-first-out convention since they are intended to be global,
while typemaps are intended to be locally specialized.
</p>

<li>
<p>
Fragment names cannot contain commas.
</p>


<li>
<p>
A fragment can use one or more additional fragments, for example:
</p>

<div class="code">
<pre>
%fragment("&lt;limits.h&gt;", "header") {
  %#include &lt;limits.h&gt;
}


%fragment("AsMyClass", "header", fragment="&lt;limits.h&gt;") {
  MyClass *AsMyClass(PyObject *obj) {
    MyClass *value = 0;

    ... some marshalling code  ...

    if  (ival &lt; CHAR_MIN /*defined in &lt;limits.h&gt;*/) {
       ...
    } else {
       ...
    }
    ...
    return value;
  }
}
</pre>
</div>

<p>
in this case, when the "AsMyClass" fragment is emitted, it also
triggers the inclusion of the "&lt;limits.h&gt;" fragment.
</p>

<li>
<p>
A fragment can have dependencies on a number of other fragments, for example:
</p>

<div class="code">
<pre>
%fragment("bigfragment", "header", fragment="frag1", fragment="frag2", fragment="frag3") "";
</pre>
</div>

<p>
When the "bigfragment" is used, the three dependent fragments "frag1",
"frag2" and "frag3" are also pulled in. Note that as "bigframent" is 
empty (the empty string - ""), it does not add any code itself, but merely triggers the
inclusion of the other fragments.
</p>

<li>
<p>
A typemap can also use more than one fragment, but since the
syntax is different, you need to specify the dependent fragments in a comma separated
list. Consider:
</p>

<div class="code">
<pre>
%typemap(in, fragment="frag1,frag2,frag3") {...}
</pre>
</div>

<p>
which is equivalent to:
</p>

<div class="code">
<pre>
%typemap(in, fragment="bigfragment") {...}
</pre>
</div>

<p>
when used with the "bigfragment" defined above.
</p>

<li>
<p>
Finally, you can force the inclusion of a fragment at any point in the generated code as follows:
</p>

<div class="code">
<pre>
%fragment("bigfragment");
</pre>
</div>

<p>
which is very useful inside a template class, for example.
</p>
</ol>

<p>
Most readers will probably want to skip the next two sub-sections on advanced
fragment usage unless a desire to really get to grips
with some powerful but tricky macro and fragment usage that is used in parts of the SWIG typemap library.
</p>

<H3><a name="Typemaps_fragment_type_specialization"></a>11.11.1 Fragment type specialization</H3>


<p>
Fragments can be <i>type specialized</i>. The syntax is as follows:
</p>

<div class="code">
<pre>
%fragment("name", "header") { ...a type independent fragment... }
%fragment("name"{type}, "header") { ...a type dependent fragment...  }
</pre>
</div>

<p>
where <tt>type</tt> is a C/C++ type. Like typemaps, fragments can also be used inside templates, for example:
</p>

<div class="code">
<pre>
template &lt;class T&gt;
struct A {
  %fragment("incode"{A&lt;T&gt;}, "header") {
    ... 'incode' specialized fragment ...
  }

  %typemap(in, fragment="incode"{A&lt;T&gt;}) {
     ... here we use the 'type specialized' fragment "incode"{A&lt;T&gt;} ...
  }
};
</pre>
</div>

<H3><a name="Typemaps_automatic_specialization"></a>11.11.2 Fragments and automatic typemap specialization</H3>


<p>
Since fragments can be type specialized, they can be elegantly used
to specialize typemaps. For example, if you have something like:
</p>

<div class="code">
<pre>
%fragment("incode"{float}, "header") {
  float in_method_float(PyObject *obj) {
    ...
  }
}

%fragment("incode"{long}, "header") {
  float in_method_long(PyObject *obj) {
    ...
  }
}

// %my_typemaps macro definition
%define %my_typemaps(Type) 
%typemap(in, fragment="incode"{Type}) Type {
  value = in_method_##Type(obj);
}
%enddef

%my_typemaps(float);
%my_typemaps(long);
</pre>
</div>

<p>
then the proper <tt>"incode"{float}</tt> or <tt>"incode"{long}</tt> fragment will be used,
and the <tt>in_method_float</tt> and <tt>in_method_long</tt> methods will be called whenever
the <tt>float</tt> or <tt>long</tt> types are used as input parameters.
</p>

<p>
This feature is used a lot in the typemaps shipped in the SWIG library for some scripting languages.
The interested (or very brave) reader can take a look at the fragments.swg file shipped with SWIG to see this in action.
</p>


<H2><a name="Typemaps_runtime_type_checker"></a>11.12 The run-time type checker</H2>


<p>
Most scripting languages need type information at run-time.  This type information
can include how to construct types, how to garbage collect types, and the inheritance
relationships between types.  If the language interface does not provide its own type
information storage, the generated SWIG code needs to provide it.
</p>

<p>
Requirements for the type system:
</p>
<ul>
<li>Store inheritance and type equivalence information and be able to correctly 
re-create the type pointer.</li>
<li>Share type information between modules.</li>
<li>Modules can be loaded in any order, regardless of actual type
dependency.</li>
<li>Avoid the use of dynamically allocated memory, and library/system calls in general.</li>
<li>Provide a reasonably fast implementation, minimizing the lookup time for all
language modules.</li>
<li>Custom, language specific information can be attached to types.</li>
<li>Modules can be unloaded from the type system.</li>
</ul>

<H3><a name="Typemaps_nn45"></a>11.12.1 Implementation</H3>


<p>
The run-time type checker is used by many, but not all, of SWIG's supported target languages.
The run-time type checker features
are not required and are thus not used for statically typed languages such as Java and C#.
The scripting and scheme based languages rely on it and it forms
a critical part of SWIG's operation for these languages.
</p>

<p>
When pointers, arrays, and objects are wrapped by SWIG, they are normally converted
into typed pointer objects.  For example, an instance of <tt>Foo *</tt> might be
a string encoded like this:
</p>

<div class="diagram">
<pre>
_108e688_p_Foo
</pre>
</div>

<p>
At a basic level, the type checker simply restores some type-safety to
extension modules.  However, the type checker is also responsible for
making sure that wrapped C++ classes are handled
correctly---especially when inheritance is used.   This is especially
important when an extension module makes use of multiple inheritance.
For example:
</p>

<div class="code">
<pre>
class Foo {
   int x;
};

class Bar {
   int y;
};

class FooBar : public Foo, public Bar {
   int z;
};
</pre>
</div>

<p>
When the class <tt>FooBar</tt> is organized in memory, it contains the contents
of the classes <tt>Foo</tt> and <tt>Bar</tt> as well as its own data members.  For example:
</p>

<div class="diagram">
<pre>
FooBar --&gt; | -----------|  &lt;-- Foo
           |   int x    |
           |------------|  &lt;-- Bar
           |   int y    |
           |------------|
           |   int z    |
           |------------|
</pre>
</div>

<p>
Because of the way that base class data is stacked together, the
casting of a <tt>Foobar *</tt> to either of the base classes may
change the actual value of the pointer.  This means that it is
generally not safe to represent pointers using a simple integer or a
bare <tt>void *</tt>---type tags are needed to implement correct
handling of pointer values (and to make adjustments when needed).   
</p>

<p>
In the wrapper code generated for each language, pointers are handled through
the use of special type descriptors and conversion functions.  For example,
if you look at the wrapper code for Python, you will see code like this:
</p>

<div class="code">
<pre>
if ((SWIG_ConvertPtr(obj0,(void **) &amp;arg1, SWIGTYPE_p_Foo,1)) == -1) return NULL;
</pre>
</div>

<p>
In this code, <tt>SWIGTYPE_p_Foo</tt> is the type descriptor that
describes <tt>Foo *</tt>.  The type descriptor is actually a pointer to a 
structure that contains information about the type name to use in the
target language, a list of equivalent typenames (via typedef or
inheritance), and pointer value handling information (if applicable).
The <tt>SWIG_ConvertPtr()</tt> function is simply a utility function
that takes a pointer object in the target language and a
type-descriptor objects and uses this information to generate a C++
pointer.  However, the exact name and calling conventions of the conversion
function depends on the target language (see language specific chapters for details). 
</p>

<p>
The actual type code is in swigrun.swg, and gets inserted near the top of the generated
swig wrapper file.  The phrase "a type X that can cast into a type Y" means
that given a type X, it can be converted into a type Y.  In other words, X is a derived
class of Y or X is a typedef of Y.  The structure to store type information looks like this:
</p>

<div class="code">
<pre>
/* Structure to store information on one type */
typedef struct swig_type_info {
  const char *name;             /* mangled name of this type */
  const char *str;              /* human readable name for this type */
  swig_dycast_func dcast;       /* dynamic cast function down a hierarchy */
  struct swig_cast_info *cast;  /* Linked list of types that can cast into this type */
  void *clientdata;             /* Language specific type data */
} swig_type_info;

/* Structure to store a type and conversion function used for casting */
typedef struct swig_cast_info {
  swig_type_info *type;          /* pointer to type that is equivalent to this type */
  swig_converter_func converter; /* function to cast the void pointers */
  struct swig_cast_info *next;   /* pointer to next cast in linked list */
  struct swig_cast_info *prev;   /* pointer to the previous cast */
} swig_cast_info;
</pre>
</div>

<p>
Each <tt>swig_type_info</tt> stores a linked list of types that it is equivalent to.  Each entry in this
doubly linked list stores a pointer back to another swig_type_info structure,
along with a pointer to a conversion function.  This conversion function is used
to solve the above problem of the FooBar class, correctly returning a pointer to
the type we want.
</p>

<p>
The basic problem we need to solve is verifying and building arguments passed to functions.
So going back to the <tt>SWIG_ConvertPtr()</tt> function example from above, we are
expecting a <tt>Foo *</tt> and need to
check if <tt>obj0</tt> is in fact a <tt>Foo *</tt>.  From before, <tt>SWIGTYPE_p_Foo</tt> is just
a pointer to the <tt>swig_type_info</tt> structure describing <tt>Foo *</tt>.  So we loop through the
linked list of <tt>swig_cast_info</tt> structures attached to <tt>SWIGTYPE_p_Foo</tt>.  If we see that the type of <tt>obj0</tt> is in the
linked list, we pass the object through the associated conversion function and
then return a positive.  If we reach the end of the linked list without a match,
then <tt>obj0</tt> can not be converted to a <tt>Foo *</tt> and an error is generated.
</p>

<p>
Another issue needing to be addressed is sharing type information between multiple modules.
More explicitly, we need
to have ONE <tt>swig_type_info</tt> for each type.  If two modules both use the type, the
second module loaded must lookup and use the swig_type_info structure from the module already loaded.
Because no dynamic memory is used and the circular dependencies of the
casting information, loading the type information is somewhat tricky, and not explained here.
A complete description is in the <tt>Lib/swiginit.swg</tt> file (and near the top of any generated file).
</p>

<p>
Each module has one swig_module_info structure which looks like this:
</p>

<div class="code">
<pre>
/* Structure used to store module information
 * Each module generates one structure like this, and the runtime collects
 * all of these structures and stores them in a circularly linked list.*/
typedef struct swig_module_info {
  swig_type_info **types;         /* Array of pointers to swig_type_info structs in this module */
  int size;                       /* Number of types in this module */
  struct swig_module_info *next;  /* Pointer to next element in circularly linked list */
  swig_type_info **type_initial;  /* Array of initially generated type structures */
  swig_cast_info **cast_initial;  /* Array of initially generated casting structures */
  void *clientdata;               /* Language specific module data */
} swig_module_info;
</pre>
</div>

<p>
Each module stores an array of pointers to <tt>swig_type_info</tt> structures and the number of
types in this module.  So when a second module is loaded, it finds the <tt>swig_module_info</tt>
structure for the first module and searches the array of types. If any of its own
types are in the first module and have already been loaded, it uses those <tt>swig_type_info</tt>
structures rather than creating new ones.  These <tt>swig_module_info</tt> 
structures are chained together in a circularly linked list.
</p>

<H3><a name="Typemaps_runtime_type_checker_usage"></a>11.12.2 Usage</H3>


<p>This section covers how to use these functions from typemaps.  To learn how to
call these functions from external files (not the generated _wrap.c file), see
the <a href="Modules.html#Modules_external_run_time">External access to the run-time system</a>
section.</p>

<p>When pointers are converted in a typemap, the typemap code often looks
similar to this:
</p>

<div class="code">
<pre>
%typemap(in) Foo * {
  if ((SWIG_ConvertPtr($input, (void **) &amp;$1, $1_descriptor)) == -1) return NULL;
}
</pre>
</div>

<p>
The most critical part is the typemap is the use of the <tt>$1_descriptor</tt>
special variable.  When placed in a typemap, this is expanded into the
<tt>SWIGTYPE_*</tt> type descriptor object above.  As a general rule,
you should always use <tt>$1_descriptor</tt> instead of trying to
hard-code the type descriptor name directly.
</p>

<p>
There is another reason why you should always use the
<tt>$1_descriptor</tt> variable.  When this special variable is
expanded, SWIG marks the corresponding type as "in use."  When
type-tables and type information is emitted in the wrapper file,
descriptor information is only generated for those datatypes that were
actually used in the interface.  This greatly reduces the size of the
type tables and improves efficiency. 
</p>

<p>
Occasionally, you might need to write a typemap that needs to convert
pointers of other types.  To handle this, the special variable macro
<tt>$descriptor(type)</tt> covered earlier can be used to generate the SWIG type
descriptor name for any C datatype.  For example:
</p>

<div class="code">
<pre>
%typemap(in) Foo * {
  if ((SWIG_ConvertPtr($input, (void **) &amp;$1, $1_descriptor)) == -1) {
     Bar *temp;
     if ((SWIG_ConvertPtr($input, (void **) &amp;temp, <b>$descriptor(Bar *)</b>) == -1) {
         return NULL;
     }
     $1 = (Foo *) temp;
  }
}
</pre>
</div>

<p>
The primary use of <tt>$descriptor(type)</tt> is when writing typemaps for container
objects and other complex data structures.  There are some restrictions on the argument---namely it must
be a fully defined C datatype.  It can not be any of the special typemap variables.
</p>

<p>
In certain cases, SWIG may not generate type-descriptors like you expect.  For example,
if you are converting pointers in some non-standard way or working with an unusual
combination of interface files and modules, you may find that SWIG omits information
for a specific type descriptor.  To fix this, you may need to use the <tt>%types</tt> directive.
For example:
</p>

<div class="code">
<pre>
%types(int *, short *, long *, float *, double *);
</pre>
</div>

<p>
When <tt>%types</tt> is used, SWIG generates type-descriptor
information even if those datatypes never appear elsewhere in the
interface file.
</p>

<p>
Further details about the run-time type checking can be found in the documentation for
individual language modules.   Reading the source code may also help.  The file
<tt>Lib/swigrun.swg</tt> in the SWIG library contains all of the source of the generated code for 
type-checking.  This code is also included in every generated wrapped file so you
probably just look at the output of SWIG to get a better sense for how types are
managed.
</p>

<H2><a name="Typemaps_overloading"></a>11.13 Typemaps and overloading</H2>


<p>
This section does not apply to the statically typed languages like Java and C#, where overloading
of the types is handled much like C++ by generating overloaded methods in the target language.
In many of the other target languages, SWIG still fully supports C++ overloaded methods and functions.   For example,
if you have a collection of functions like this:
</p>

<div class="code">
<pre>
int foo(int x);
int foo(double x);
int foo(char *s, int y);
</pre>
</div>

<p>
You can access the functions in a normal way from the scripting interpreter:
</p>

<div class="targetlang">
<pre>
# Python
foo(3)           # foo(int)
foo(3.5)         # foo(double)
foo("hello",5)   # foo(char *, int)

# Tcl
foo 3            # foo(int)
foo 3.5          # foo(double)
foo hello 5      # foo(char *, int)
</pre>
</div>

<p>
To implement overloading, SWIG generates a separate wrapper function for each overloaded method.
For example, the above functions would produce something roughly like this:
</p>

<div class="code">
<pre>
// wrapper pseudocode
_wrap_foo_0(argc, args[]) {       // foo(int)
   int arg1;
   int result;
   ...
   arg1 = FromInteger(args[0]);
   result = foo(arg1);
   return ToInteger(result);
}

_wrap_foo_1(argc, args[]) {       // foo(double)
   double arg1;
   int result;
   ...
   arg1 = FromDouble(args[0]);
   result = foo(arg1);
   return ToInteger(result);
}

_wrap_foo_2(argc, args[]) {       // foo(char *, int)
   char *arg1;
   int   arg2;
   int result;
   ...
   arg1 = FromString(args[0]);
   arg2 = FromInteger(args[1]);
   result = foo(arg1,arg2);
   return ToInteger(result);
}

</pre>
</div>

<p>
Next, a dynamic dispatch function is generated:
</p>

<div class="code">
<pre>
_wrap_foo(argc, args[]) {
   if (argc == 1) {
       if (IsInteger(args[0])) {
           return _wrap_foo_0(argc,args);
       } 
       if (IsDouble(args[0])) {
           return _wrap_foo_1(argc,args);
       }
   }
   if (argc == 2) {
       if (IsString(args[0]) &amp;&amp; IsInteger(args[1])) {
          return _wrap_foo_2(argc,args);
       }
   }
   error("No matching function!\n");
}
</pre>
</div>

<p>
The purpose of the dynamic dispatch function is to select the appropriate C++ function based on 
argument types---a task that must be performed at runtime in most of SWIG's target languages.
</p>

<p>
The generation of the dynamic dispatch function is a relatively tricky affair.  Not only must input typemaps
be taken into account (these typemaps can radically change the types of arguments accepted), but overloaded
methods must also be sorted and checked in a very specific order to resolve potential ambiguity.   A high-level
overview of this ranking process is found in the "<a href="SWIGPlus.html#SWIGPlus">SWIG and C++</a>" chapter.    What isn't mentioned in that chapter
is the mechanism by which it is implemented---as a collection of typemaps.
</p>

<p>
To support dynamic dispatch, SWIG first defines a general purpose type hierarchy as follows:
</p>

<div class="diagram">
<pre>
Symbolic Name                   Precedence Value
------------------------------  ------------------
SWIG_TYPECHECK_POINTER           0  
SWIG_TYPECHECK_VOIDPTR           10 
SWIG_TYPECHECK_BOOL              15 
SWIG_TYPECHECK_UINT8             20 
SWIG_TYPECHECK_INT8              25 
SWIG_TYPECHECK_UINT16            30 
SWIG_TYPECHECK_INT16             35 
SWIG_TYPECHECK_UINT32            40 
SWIG_TYPECHECK_INT32             45 
SWIG_TYPECHECK_UINT64            50 
SWIG_TYPECHECK_INT64             55 
SWIG_TYPECHECK_UINT128           60 
SWIG_TYPECHECK_INT128            65 
SWIG_TYPECHECK_INTEGER           70 
SWIG_TYPECHECK_FLOAT             80 
SWIG_TYPECHECK_DOUBLE            90 
SWIG_TYPECHECK_COMPLEX           100 
SWIG_TYPECHECK_UNICHAR           110 
SWIG_TYPECHECK_UNISTRING         120 
SWIG_TYPECHECK_CHAR              130 
SWIG_TYPECHECK_STRING            140 
SWIG_TYPECHECK_BOOL_ARRAY        1015 
SWIG_TYPECHECK_INT8_ARRAY        1025 
SWIG_TYPECHECK_INT16_ARRAY       1035 
SWIG_TYPECHECK_INT32_ARRAY       1045 
SWIG_TYPECHECK_INT64_ARRAY       1055 
SWIG_TYPECHECK_INT128_ARRAY      1065 
SWIG_TYPECHECK_FLOAT_ARRAY       1080 
SWIG_TYPECHECK_DOUBLE_ARRAY      1090 
SWIG_TYPECHECK_CHAR_ARRAY        1130 
SWIG_TYPECHECK_STRING_ARRAY      1140 
</pre>
</div>

<p>
(These precedence levels are defined in <tt>swig.swg</tt>, a library file that's included by all target language modules.)
</p>

<p>
In this table, the precedence-level determines the order in which types are going to be checked.  Low values
are always checked before higher values.  For example, integers are checked before floats, single values are checked
before arrays, and so forth.
</p>

<p>
Using the above table as a guide, each target language defines a collection of "typecheck" typemaps. 
The follow excerpt from the Python module illustrates this:
</p>

<div class="code">
<pre>
/* Python type checking rules */
/* Note:  %typecheck(X) is a macro for %typemap(typecheck,precedence=X) */

%typecheck(SWIG_TYPECHECK_INTEGER)
	 int, short, long,
 	 unsigned int, unsigned short, unsigned long,
	 signed char, unsigned char,
	 long long, unsigned long long,
	 const int &amp;, const short &amp;, const long &amp;,
 	 const unsigned int &amp;, const unsigned short &amp;, const unsigned long &amp;,
	 const long long &amp;, const unsigned long long &amp;,
	 enum SWIGTYPE,
         bool, const bool &amp; 
{
  $1 = (PyInt_Check($input) || PyLong_Check($input)) ? 1 : 0;
}

%typecheck(SWIG_TYPECHECK_DOUBLE)
	float, double,
	const float &amp;, const double &amp;
{
  $1 = (PyFloat_Check($input) || PyInt_Check($input) || PyLong_Check($input)) ? 1 : 0;
}

%typecheck(SWIG_TYPECHECK_CHAR) char {
  $1 = (PyString_Check($input) &amp;&amp; (PyString_Size($input) == 1)) ? 1 : 0;
}

%typecheck(SWIG_TYPECHECK_STRING) char * {
  $1 = PyString_Check($input) ? 1 : 0;
}

%typecheck(SWIG_TYPECHECK_POINTER) SWIGTYPE *, SWIGTYPE &amp;, SWIGTYPE [] {
  void *ptr;
  if (SWIG_ConvertPtr($input, (void **) &amp;ptr, $1_descriptor, 0) == -1) {
    $1 = 0;
    PyErr_Clear();
  } else {
    $1 = 1;
  }
}

%typecheck(SWIG_TYPECHECK_POINTER) SWIGTYPE {
  void *ptr;
  if (SWIG_ConvertPtr($input, (void **) &amp;ptr, $&amp;1_descriptor, 0) == -1) {
    $1 = 0;
    PyErr_Clear();
  } else {
    $1 = 1;
  }
}

%typecheck(SWIG_TYPECHECK_VOIDPTR) void * {
  void *ptr;
  if (SWIG_ConvertPtr($input, (void **) &amp;ptr, 0, 0) == -1) {
    $1 = 0;
    PyErr_Clear();
  } else {
    $1 = 1;
  }
}

%typecheck(SWIG_TYPECHECK_POINTER) PyObject *
{
  $1 = ($input != 0);
}
</pre>
</div>

<p>
It might take a bit of contemplation, but this code has merely organized all of the basic C++ types, provided some simple type-checking
code, and assigned each type a precedence value.
</p>

<p>
Finally, to generate the dynamic dispatch function, SWIG uses the following algorithm:
</p>

<ul>
<li>Overloaded methods are first sorted by the number of required arguments.</li>
<li>Methods with the same number of arguments are then sorted by precedence values of argument types.</li>
<li>Typecheck typemaps are then emitted to produce a dispatch function that checks arguments in the correct order.</li>
</ul>

<p>
If you haven't written any typemaps of your own, it is unnecessary to worry about the typechecking rules.
However, if you have written new input typemaps, you might have to supply a typechecking rule as well.
An easy way to do this is to simply copy one of the existing typechecking rules. 
Here is an example,
</p>

<div class="code">
<pre>
// Typemap for a C++ string
%typemap(in) std::string {
    if (PyString_Check($input)) {
         $1 = std::string(PyString_AsString($input));
     } else {
         SWIG_exception(SWIG_TypeError, "string expected");
     }
}
// Copy the typecheck code for "char *".  
%typemap(typecheck) std::string = char *;
</pre>
</div>

<p>
The bottom line:  If you are writing new typemaps and you are using overloaded methods, you will probably 
have to write typecheck code or copy existing code.   Since this is a relatively new SWIG feature, there are
few examples to work with.  However, you might look at some of the existing library files likes 'typemaps.i' for
a guide.
</p>

<p>
<b>Notes:</b>
</p>

<ul>
<li>Typecheck typemaps are not used for non-overloaded methods.  Because of this, it is
still always necessary to check types in any "in" typemaps.
</li>

<li>The dynamic dispatch process is only meant to be a heuristic.  There are many corner
cases where SWIG simply can't disambiguate types to the same degree as C++.   The only way to
resolve this ambiguity is to use the %rename directive to rename one of the overloaded methods (effectively
eliminating overloading).
</li>

<li>
Typechecking may be partial.  For example, if working with arrays, the typecheck code might 
simply check the type of the first array element and use that to dispatch to the correct function.
Subsequent "in" typemaps would then perform more extensive type-checking.
</li>

<li>Make sure you read the section on overloading in the "<a href="SWIGPlus.html#SWIGPlus">SWIG and C++</a>" chapter.
</li>
</ul>

<H2><a name="Typemaps_nn48"></a>11.14 More about <tt>%apply</tt> and <tt>%clear</tt></H2>


<p>
In order to implement certain kinds of program behavior, it is sometimes necessary to
write sets of typemaps.  For example, to support output arguments, one often writes
a set of typemaps like this:
</p>

<div class="code">
<pre>
%typemap(in,numinputs=0) int *OUTPUT (int temp) {
   $1 = &amp;temp;
}
%typemap(argout) int *OUTPUT {
   // return value somehow
}
</pre>
</div>

<p>
To make it easier to apply the typemap to different argument types and names, the <tt>%apply</tt> directive
performs a copy of all typemaps from one type to another.  For example, if you specify this,
</p>

<div class="code">
<pre>
%apply int *OUTPUT { int *retvalue, int32 *output };
</pre>
</div>

<p>
then all of the <tt>int *OUTPUT</tt> typemaps are copied to <tt>int *retvalue</tt> and <tt>int32 *output</tt>.
</p>

<p>
However, there is a subtle aspect of <tt>%apply</tt> that needs more description.  Namely, <tt>%apply</tt> does not
overwrite a typemap rule if it is already defined for the target datatype.   This behavior allows you to do two things:
</p>

<ul>
<li>You can specialize parts of a complex typemap rule by first defining a few typemaps and then using
<tt>%apply</tt> to incorporate the remaining pieces.
</li>

<li>Sets of different typemaps can be applied to the same datatype using repeated <tt>%apply</tt> directives.
</li>
</ul>

<p>
For example:
</p>

<div class="code">
<pre>
%typemap(in) int *INPUT (int temp) {
   temp = ... get value from $input ...;
   $1 = &amp;temp;
}

%typemap(check) int *POSITIVE {
   if (*$1 &lt;= 0) {
      SWIG_exception(SWIG_ValueError,"Expected a positive number!\n");
      return NULL;
   }
}

...
%apply int *INPUT     { int *invalue };
%apply int *POSITIVE  { int *invalue };
</pre>
</div>

<p>
Since <tt>%apply</tt> does not overwrite or replace any existing rules, the only way to reset behavior is to
use the <tt>%clear</tt> directive.  <tt>%clear</tt> removes all typemap rules defined for a specific datatype.  For
example:
</p>

<div class="code">
<pre>
%clear int *invalue;
</pre>
</div>


<H2><a name="Typemaps_nn47"></a>11.15 Passing data between typemaps</H2>


<p>
It is also important to note that the primary use of local variables
is to create stack-allocated objects for temporary use inside a
wrapper function (this is faster and less-prone to error than
allocating data on the heap).  In general, the variables are not intended
to pass information between different types of typemaps.  However, this
can be done if you realize that local names have the argument number appended
to them.  For example, you could do this:
</p>

<div class="code">
<pre>
%typemap(in) int *(int temp) {
   temp = (int) PyInt_AsLong($input);
   $1 = &amp;temp;
}

%typemap(argout) int * {
   PyObject *o = PyInt_FromLong(temp$argnum);
   ...
}
</pre>
</div>

<p>
In this case, the <tt>$argnum</tt> variable is expanded into the argument
number.  Therefore, the code will reference the appropriate local
such as <tt>temp1</tt> and <tt>temp2</tt>.   It should be noted that there are 
plenty of opportunities to break the universe here and that accessing locals
in this manner should probably be avoided.  At the very least, you should make
sure that the typemaps sharing information have exactly the same types and names.
</p>


<H2><a name="Typemaps_nn52"></a>11.16 C++ "this" pointer</H2>


<p>
All the rules discussed for typemaps apply to C++ as well as C.
However in addition C++ passes an extra parameter into every
non-static class method -- the <tt>this</tt> pointer.  Occasionally it can be
useful to apply a typemap to this pointer (for example to check
and make sure <tt>this</tt> is non-null before deferencing).
Actually, C also has an the equivalent of the <tt>this</tt> pointer which is used
when accessing variables in a C struct.
</p>
<p>
In order to customise the <tt>this</tt> pointer handling, target a variable named <tt>self</tt> in your typemaps.
<tt>self</tt> is the name SWIG uses to refer to the extra parameter in wrapped functions. 
</p>
<p>
For example, if wrapping for Java generation:
</p>

<div class="code">
<pre>
%typemap(check) SWIGTYPE *self %{
if (!$1) {
  SWIG_JavaThrowException(jenv, SWIG_JavaNullPointerException,
    "invalid native object; delete() likely already called");
  return $null;
}
%}
</pre>
</div>

<p>
In the above case, the <tt>$1</tt> variable is expanded into the argument
name that SWIG is using as the <tt>this</tt> pointer.

SWIG will then insert the check code before the actual C++ class method
is called, and will raise an exception rather than crash
the Java virtual machine.

The generated code will look something like:
</p>

<div class="code">
<pre>
  if (!arg1) {
    SWIG_JavaThrowException(jenv, SWIG_JavaNullPointerException,
      "invalid native object; delete() likely already called");
    return ;
  }
  (arg1)-&gt;wrappedFunction(...);
</pre>
</div>

<p>
Note that if you have a parameter named <tt>self</tt> then it
will also match the typemap.  One work around is to create an interface file that wraps
the method, but gives the argument a name other than <tt>self</tt>.
</p>

<H2><a name="Typemaps_nn51"></a>11.17 Where to go for more information?</H2>


<p>
The
best place to find out more information about writing typemaps is to
look in the SWIG library.  Most language modules define all of their
default behavior using typemaps.  These are found in files such as
<tt>python.swg</tt>, <tt>perl5.swg</tt>, <tt>tcl8.swg</tt> and so
forth.  The <tt>typemaps.i</tt> file in the library also contains
numerous examples.   You should look at these files to get a feel
for how to define typemaps of your own.
Some of the language modules support additional typemaps and further
information is available in the individual chapters for each target language.
There you may also find more hands-on practical examples.
</p>

</body>
</html>
View Lorry Controller Status