Add std::string constructor for substring of string_view (LWG 2742)

	* doc/xml/manual/intro.xml: Document LWG 2742 status.
	* doc/html/*: Regenerate.
	* include/bits/basic_string.h
	(basic_string(const T&, size_type, size_type, const Allocator&)): Add
	constructor for substring of basic_string_view, as per LWG 2742 but
	with additional constraint to fix ambiguity.
	* testsuite/21_strings/basic_string/cons/char/9.cc: New test.
	* testsuite/21_strings/basic_string/cons/wchar_t/9.cc: New test.

From-SVN: r242416

1 files changed, 46 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/9.cc b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/9.cc
new file mode 100644
index 00000000000..0024ffc8894
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string/cons/char/9.cc
@@ -0,0 +1,46 @@
+// Copyright (C) 2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++1z } }
+
+#include <string>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  using C = char;
+  using string_type = std::basic_string<C>;
+  using view_type = std::basic_string_view<C>;
+
+  std::allocator<C> alloc;
+  VERIFY( string_type(view_type("string")) == "string" );
+  VERIFY( string_type(view_type("string"), alloc) == "string" );
+
+  // LWG 2742
+  VERIFY( string_type("substring", 3, 6) == "string" );
+  VERIFY( string_type("substring", 3, 6, alloc) == "string" );
+  VERIFY( string_type(view_type("substring"), 3, 6) == "string" );
+  VERIFY( string_type(view_type("substring"), 3, 6, alloc) == "string" );
+}
+
+int
+main()
+{
+  test01();
+}