1 // { dg-options "-std=gnu++17" } 2 3 // Copyright (C) 2016-2019 Free Software Foundation, Inc. 4 // 5 // This file is part of the GNU ISO C++ Library. This library is free 6 // software; you can redistribute it and/or modify it under the 7 // terms of the GNU General Public License as published by the 8 // Free Software Foundation; either version 3, or (at your option) 9 // any later version. 10 11 // This library is distributed in the hope that it will be useful, 12 // but WITHOUT ANY WARRANTY; without even the implied warranty of 13 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 14 // GNU General Public License for more details. 15 16 // You should have received a copy of the GNU General Public License along 17 // with this library; see the file COPYING3. If not see 18 // <http://www.gnu.org/licenses/>. 19 20 #include <optional> 21 #include <testsuite_hooks.h> 22 23 class S{}; // No hash specialization 24 25 template<class T> 26 auto f(int) -> decltype(std::hash<std::optional<T>>(), std::true_type()); 27 28 template<class T> 29 auto f(...) -> decltype(std::false_type()); 30 31 static_assert(!decltype(f<S>(0))::value, ""); 32 33 template<typename T> hashable()34constexpr bool hashable() 35 { return std::is_invocable_v<std::hash<T>&, const T&>; } 36 37 static_assert(!hashable<std::optional<S>>()); 38 static_assert(!hashable<std::optional<const S>>()); 39 static_assert(hashable<std::optional<int>>()); 40 static_assert(hashable<std::optional<const int>>()); 41 main()42int main() 43 { 44 int x = 42; 45 std::optional<int> x2 = 42; 46 VERIFY(std::hash<int>()(x) == std::hash<std::optional<int>>()(x2)); 47 48 // PR libstdc++/82262 49 std::optional<const int> x3 = x2; 50 VERIFY(std::hash<int>()(x) == std::hash<std::optional<const int>>()(x3)); 51 } 52