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Implement LWG 2825, LWG 2756 breaks class template argument deduction for optional. 

* include/std/optional: Add a deduction guide.
* testsuite/20_util/optional/cons/deduction_guide.cc: New.

From-SVN: r245024
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Ville Voutilainen 2017-01-30 15:37:16 +02:00 committed by Ville Voutilainen
parent 87c45ec798
commit 1dd9523917
3 changed files with 53 additions and 0 deletions
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7
libstdc++-v3/ChangeLog
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@ -1,3 +1,10 @@
2017-01-30 Ville Voutilainen <ville.voutilainen@gmail.com>
Implement LWG 2825, LWG 2756 breaks class template argument
deduction for optional.
* include/std/optional: Add a deduction guide.
* testsuite/20_util/optional/cons/deduction_guide.cc: New.
2017-01-27 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/79254

2
libstdc++-v3/include/std/optional
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@ -981,6 +981,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// @}
template <typename _Tp> optional(_Tp) -> optional<_Tp>;
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std

44
libstdc++-v3/testsuite/20_util/optional/cons/deduction_guide.cc Normal file
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@ -0,0 +1,44 @@
// { dg-options "-std=gnu++17" }
// { dg-do compile }
// 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/>.
#include <optional>
#include <type_traits>
struct MoveOnly
{
MoveOnly() = default;
MoveOnly(MoveOnly&&) {}
MoveOnly& operator=(MoveOnly&&) {}
};
int main()
{
std::optional x = 5;
static_assert(std::is_same_v<decltype(x), std::optional<int>>);
int y = 42;
std::optional x2 = y;
static_assert(std::is_same_v<decltype(x2), std::optional<int>>);
const int z = 666;
std::optional x3 = z;
static_assert(std::is_same_v<decltype(x3), std::optional<int>>);
std::optional mo = MoveOnly();
static_assert(std::is_same_v<decltype(mo), std::optional<MoveOnly>>);
mo = MoveOnly();
}