re PR libstdc++/57336 (Cannot INVOKE a reference_wrapper around an abstract type)

	PR libstdc++/57336
	* include/std/functional (__invoke): Do not form function types with
	abstract return type.
	* testsuite/20_util/reference_wrapper/invoke-3.cc: New.

From-SVN: r199136

libstdc++-v3/ChangeLog

+2013-05-21  Jonathan Wakely  <jwakely.gcc@gmail.com>
+
+	PR libstdc++/57336
+	* include/std/functional (__invoke): Do not form function types with
+	abstract return type.
+	* testsuite/20_util/reference_wrapper/invoke-3.cc: New.
+
 2013-05-19  Jonathan Wakely  <jwakely.gcc@gmail.com>
 
 	* include/std/tuple (get): Implement N3670.

libstdc++-v3/include/std/functional

@@ -195,7 +195,7 @@ _GLIBCXX_HAS_NESTED_TYPE(result_type)
 	     (!is_member_pointer<_Functor>::value
 	      && !is_function<_Functor>::value
 	      && !is_function<typename remove_pointer<_Functor>::type>::value),
-	     typename result_of<_Functor(_Args&&...)>::type
+	     typename result_of<_Functor&(_Args&&...)>::type
 	   >::type
     __invoke(_Functor& __f, _Args&&... __args)
     {

libstdc++-v3/testsuite/20_util/reference_wrapper/invoke-3.cc

+// { dg-options "-std=gnu++11" }
+// { dg-do compile }
+
+// Copyright (C) 2013 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/>.
+
+// 20.8.3.4 reference_wrapper invocation [refwrap.invoke]
+#include <functional>
+
+struct ABC
+{
+    virtual bool operator()() const = 0;
+};
+
+struct Concrete : ABC
+{
+    virtual bool operator()() const { return true; }
+};
+
+Concrete c;
+ABC& abc = c;
+
+auto b = std::cref(abc)();