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

   1 // { dg-options "-std=gnu++17" }
   2
   3 // Copyright (C) 2016-2020 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>
  34 constexpr 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
  42 int 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 }