PR libstdc++/79486 use lvalues in result_of expressions

	PR libstdc++/79486
	* include/std/future (__future_base::_Task_state::_M_run)
	(__future_base::_Task_state::_M_run_delayed): Use lvalue types in
	result_of expressions.
	* testsuite/30_threads/packaged_task/79486.cc: New.

From-SVN: r245386

libstdc++-v3/ChangeLog

+2017-02-13  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/79486
+	* include/std/future (__future_base::_Task_state::_M_run)
+	(__future_base::_Task_state::_M_run_delayed): Use lvalue types in
+	result_of expressions.
+	* testsuite/30_threads/packaged_task/79486.cc: New.
+
 2017-02-11  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/79467

libstdc++-v3/include/std/future

@@ -1416,7 +1416,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       virtual void
       _M_run(_Args&&... __args)
       {
-	auto __boundfn = [&] () -> typename result_of<_Fn(_Args&&...)>::type {
+	auto __boundfn = [&] () -> typename result_of<_Fn&(_Args&&...)>::type {
 	    return std::__invoke(_M_impl._M_fn, std::forward<_Args>(__args)...);
 	};
 	this->_M_set_result(_S_task_setter(this->_M_result, __boundfn));
@@ -1425,7 +1425,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       virtual void
       _M_run_delayed(_Args&&... __args, weak_ptr<_State_base> __self)
       {
-	auto __boundfn = [&] () -> typename result_of<_Fn(_Args&&...)>::type {
+	auto __boundfn = [&] () -> typename result_of<_Fn&(_Args&&...)>::type {
 	    return std::__invoke(_M_impl._M_fn, std::forward<_Args>(__args)...);
 	};
 	this->_M_set_delayed_result(_S_task_setter(this->_M_result, __boundfn),

libstdc++-v3/testsuite/30_threads/packaged_task/79486.cc

+// Copyright (C) 2017 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-do compile { target c++11 } }
+
+#include <future>
+
+struct F {
+  void operator()() & { }
+  void operator()() && = delete; // PR libstdc++/79486
+};
+
+std::packaged_task<void()> t{F{}};