46 lines
1.4 KiB
C++
46 lines
1.4 KiB
C++
// Copyright (C) 2015-2016 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-options "-std=gnu++1z" }
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// { dg-do compile }
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#include <type_traits>
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#ifndef __cpp_lib_void_t
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# error "Feature-test macro for void_t missing"
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#elif __cpp_lib_void_t != 201411
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# error "Feature-test macro for void_t has wrong value"
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#endif
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static_assert( std::is_same<std::void_t<int, long, double>, void>::value,
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"void_t is a synonym for void" );
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struct X { };
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X operator+(const X& x) { return x; }
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template<typename T, typename U = std::void_t<>>
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struct has_unary_plus
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: std::false_type
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{ };
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template<typename T>
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struct has_unary_plus<T, std::void_t<decltype(+std::declval<X>())>>
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: std::true_type
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{ };
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static_assert( has_unary_plus<X>::value, "void_t detects valid expressions" );
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