libstdc++-v3/testsuite/20_util/variant/hash.cc

   1 // { dg-options "-std=gnu++17" }
   2 // { dg-do run { target c++17 } }
   3
   4 // Copyright (C) 2016-2020 Free Software Foundation, Inc.
   5 //
   6 // This file is part of the GNU ISO C++ Library.  This library is free
   7 // software; you can redistribute it and/or modify it under the
   8 // terms of the GNU General Public License as published by the
   9 // Free Software Foundation; either version 3, or (at your option)
  10 // any later version.
  11
  12 // This library is distributed in the hope that it will be useful,
  13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 // GNU General Public License for more details.
  16
  17 // You should have received a copy of the GNU General Public License along
  18 // with this library; see the file COPYING3.  If not see
  19 // <http://www.gnu.org/licenses/>.
  20
  21 #include <variant>
  22 #include <testsuite_hooks.h>
  23
  24 class S{}; // No hash specialization
  25
  26 template<class T>
  27 auto f(int) -> decltype(std::hash<std::variant<T>>(), std::true_type());
  28
  29 template<class T>
  30 auto f(...) -> decltype(std::false_type());
  31
  32 static_assert(!decltype(f<S>(0))::value, "");
  33 static_assert(!decltype(f<std::variant<S>>(0))::value, "");
  34 static_assert(!decltype(f<std::variant<S, S>>(0))::value, "");
  35 static_assert(decltype(f<std::variant<int>>(0))::value, "");
  36 static_assert(decltype(f<std::variant<int, int>>(0))::value, "");
  37 static_assert(!std::is_invocable_v<
  38     std::hash<std::variant<S>>&, std::variant<S> const&> );
  39 static_assert(!std::is_invocable_v<
  40     std::hash<std::variant<S, int>>&, std::variant<S, int> const&> );
  41 static_assert(std::is_invocable_v<
  42     std::hash<std::variant<int>>&, std::variant<int> const&> );
  43 static_assert(std::is_invocable_v<
  44     std::hash<std::variant<int, int>>&, std::variant<int, int> const&> );
  45
  46 int main()
  47 {
  48   int x = 42;
  49   std::variant<int> x2 = 42;
  50   VERIFY(std::hash<int>()(x) == std::hash<std::variant<int>>()(x2));
  51 }