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Constrain swap overload for std::optional (LWG 2748) 

* doc/xml/manual/intro.xml: Document LWG 2748 status.
	* include/std/optional (optional<T>::swap): Use is_nothrow_swappable_v
	for exception specification.
	(swap(optional<T>&, optional<T>&)): Disable when T is not swappable.
	* testsuite/20_util/optional/swap/2.cc: New test.

From-SVN: r242415
This commit is contained in:
Jonathan Wakely 2016-11-15 14:33:09 +00:00 committed by Jonathan Wakely
parent b229ab2a71
commit 8b99f005cb
4 changed files with 67 additions and 3 deletions
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8
libstdc++-v3/ChangeLog
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@ -1,3 +1,11 @@
2016-11-15 Jonathan Wakely <jwakely@redhat.com>
* doc/xml/manual/intro.xml: Document LWG 2748 status.
* include/std/optional (optional<T>::swap): Use is_nothrow_swappable_v
for exception specification.
(swap(optional<T>&, optional<T>&)): Disable when T is not swappable.
* testsuite/20_util/optional/swap/2.cc: New test.
2016-11-14 Ville Voutilainen <ville.voutilainen@gmail.com>
Implement P0513R0, Poisoning the Hash.

10
libstdc++-v3/doc/xml/manual/intro.xml
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@ -1094,7 +1094,7 @@ requirements of the license of GCC.
</para></listitem></varlistentry>
<varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-defects.html#2583">2583</link>:
<emphasis>There is no way to supply an allocator for <code> basic_string(str, pos)</code>
<emphasis>There is no way to supply an allocator for <code>basic_string(str, pos)</code>
</emphasis>
</term>
<listitem><para>Add new constructor
@ -1107,6 +1107,14 @@ requirements of the license of GCC.
<listitem><para>Define the <code>value_compare</code> typedef.
</para></listitem></varlistentry>
<varlistentry><term><link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="../ext/lwg-defects.html#2748">2748</link>:
<emphasis>swappable traits for optionals
</emphasis>
</term>
<listitem><para>Disable the non-member <code>swap</code> overload when
the contained object is not swappable.
</para></listitem></varlistentry>
</variablelist>
</section>

7
libstdc++-v3/include/std/optional
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@ -613,7 +613,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
void
swap(optional& __other)
noexcept(is_nothrow_move_constructible<_Tp>()
&& noexcept(swap(declval<_Tp&>(), declval<_Tp&>())))
&& is_nothrow_swappable_v<_Tp>)
{
using std::swap;
@ -920,8 +920,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{ return !__rhs || __lhs >= *__rhs; }
// Swap and creation functions.
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2748. swappable traits for optionals
template<typename _Tp>
inline void
inline enable_if_t<is_move_constructible_v<_Tp> && is_swappable_v<_Tp>>
swap(optional<_Tp>& __lhs, optional<_Tp>& __rhs)
noexcept(noexcept(__lhs.swap(__rhs)))
{ __lhs.swap(__rhs); }

45
libstdc++-v3/testsuite/20_util/optional/swap/2.cc Normal file
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@ -0,0 +1,45 @@
// { dg-options "-std=gnu++17" }
// { dg-do compile }
// 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/>.
#include <optional>
// Swappable.
struct A { };
static_assert( std::is_nothrow_swappable_v<A> );
static_assert( std::is_nothrow_swappable_v<std::optional<A>> );
// Swappable, but might throw.
struct B { };
void swap(B&, B&) noexcept(false);
static_assert( std::is_swappable_v<std::optional<B>> );
static_assert( !std::is_nothrow_swappable_v<std::optional<B>> );
// Not swappable, but optional<C> is swappable via the generic std::swap.
struct C { };
void swap(C&, C&) = delete;
static_assert( std::is_swappable_v<std::optional<C>> );
// Not swappable, and optional<D> not swappable via the generic std::swap.
struct D { D(D&&) = delete; };
static_assert( !std::is_swappable_v<std::optional<D>> );