| // Copyright (C) 2015-2021 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++17 } } |
| |
| #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" ); |
