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type_traits (void_t): Add. 

* include/std/type_traits (void_t): Add.
	* testsuite/20_util/void_t/1.cc: New.

From-SVN: r222522
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Jonathan Wakely 2015-04-28 13:07:34 +01:00 committed by Jonathan Wakely
parent 6b241bd157
commit bd1eb5e092
3 changed files with 56 additions and 0 deletions
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5
libstdc++-v3/ChangeLog
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@ -1,3 +1,8 @@
2015-04-28 Jonathan Wakely <jwakely@redhat.com>
* include/std/type_traits (void_t): Add.
* testsuite/20_util/void_t/1.cc: New.
2015-04-28 Tim Shen <timshen@google.com> 2015-04-28 Tim Shen <timshen@google.com>
* include/bits/regex.tcc: Handle regex_constants::__polynomial. * include/bits/regex.tcc: Handle regex_constants::__polynomial.

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libstdc++-v3/include/std/type_traits
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@ -2406,6 +2406,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename...> using __void_t = void; template<typename...> using __void_t = void;
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
#define __cpp_lib_void_t 201411
/// A metafunction that always yields void, used for detecting valid types.
template<typename...> using void_t = void;
#endif
/// @} group metaprogramming /// @} group metaprogramming
/** /**

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libstdc++-v3/testsuite/20_util/void_t/1.cc Normal file
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@ -0,0 +1,45 @@
// Copyright (C) 2015 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-options "-std=gnu++1z" }
// { dg-do compile }
#include <type_traits>
#ifndef __cpp_lib_void_t
# error "Feature-test macro for void_t missing"
#elif __cpp_lib_void_t != 201411
# error "Feature-test macro for void_t has wrong value"
#endif
static_assert( std::is_same<std::void_t<int, long, double>, void>::value,
"void_t is a synonym for void" );
struct X { };
X operator+(const X& x) { return x; }
template<typename T, typename U = std::void_t<>>
struct has_unary_plus
: std::false_type
{ };
template<typename T>
struct has_unary_plus<T, std::void_t<decltype(+std::declval<X>())>>
: std::true_type
{ };
static_assert( has_unary_plus<X>::value, "void_t detects valid expressions" );