test/std/utilities/tuple/tuple.tuple/tuple.helper/tuple_size_value_sfinae.pass.cpp

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// <tuple>

// template <class... Types> class tuple;

// template <class... Types>
//   class tuple_size<tuple<Types...>>
//     : public integral_constant<size_t, sizeof...(Types)> { };

// UNSUPPORTED: c++98, c++03

#include <tuple>
#include <type_traits>

#include "test_macros.h"

template <class T, class = decltype(std::tuple_size<T>::value)>
constexpr bool has_value(int) { return true; }
template <class> constexpr bool has_value(long) { return false; }
template <class T> constexpr bool has_value() { return has_value<T>(0); }

struct Dummy {};

int main(int, char**) {
  // Test that the ::value member does not exist
  static_assert(has_value<std::tuple<int> const>(), "");
  static_assert(has_value<std::pair<int, long> volatile>(), "");
  static_assert(!has_value<int>(), "");
  static_assert(!has_value<const int>(), "");
  static_assert(!has_value<volatile void>(), "");
  static_assert(!has_value<const volatile std::tuple<int>&>(), "");

  return 0;
}