Value type of map need not be default copyable

[Ollie Wild]

Patch courtesy Richard Smith at Google:

Fix bug in the implementation of std::map's operator[]. Construct an
object of type value_type, rather than using std::make_pair, so as to
allow mapped_type to have an *explicit* copy constructor.

See [map.access] (23.4.4.3)/5 for the corresponding standardese.

Tested via bootstrap + test.

Okay for trunk?

Thanks,
Ollie


2012-08-02  Ollie Wild  <a...@google.com>
            Richard Smith  <richardsm...@google.com>

        * include/bits/stl_map.h (operator[](key_type&&)): Replace
        std::make_pair with value_type.
        * testsuite/23_containers/map/operators/2.cc: New test.

diff --git a/libstdc++-v3/include/bits/stl_map.h 
b/libstdc++-v3/include/bits/stl_map.h
index cfd478a..a3abdd4 100644
--- a/libstdc++-v3/include/bits/stl_map.h
+++ b/libstdc++-v3/include/bits/stl_map.h
@@ -475,7 +475,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
        iterator __i = lower_bound(__k);
        // __i->first is greater than or equivalent to __k.
        if (__i == end() || key_comp()(__k, (*__i).first))
-          __i = insert(__i, std::make_pair(std::move(__k), mapped_type()));
+          __i = insert(__i, value_type(std::move(__k), mapped_type()));
        return (*__i).second;
       }
 #endif
diff --git a/libstdc++-v3/testsuite/23_containers/map/operators/2.cc 
b/libstdc++-v3/testsuite/23_containers/map/operators/2.cc
new file mode 100644
index 0000000..ce633d7
--- /dev/null
+++ b/libstdc++-v3/testsuite/23_containers/map/operators/2.cc
@@ -0,0 +1,38 @@
+// Copyright (C) 2012
+// 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/>.
+
+// 23.4.4 template class map
+
+// This test verifies that the value type of a map need not be default
+// copyable.
+
+// { dg-do compile }
+// { dg-options "-std=gnu++11" }
+
+#include <map>
+
+struct Mapped {
+    Mapped();
+    explicit Mapped(const Mapped&);
+};
+
+Mapped & foo()
+{
+  std::map<int, Mapped> m;
+  return m[0];
+}