libcxx/test/std/utilities/optional/optional.nullopt/compare.three_way.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
//
//===----------------------------------------------------------------------===//

// REQUIRES: std-at-least-c++17

// <optional>

// struct nullopt_t{see below};
// inline constexpr nullopt_t nullopt(unspecified);

// [optional.nullopt]/2:
//  nullopt_t models copyable and three_way_comparable<strong_ordering>.

#include <algorithm>
#include <cassert>
#include <concepts>
#include <optional>
#include <vector>

#include "test_macros.h"

#if TEST_STD_VER >= 20
static_assert(std::copyable<std::nullopt_t>);
static_assert(std::three_way_comparable<std::nullopt_t, std::strong_ordering>);
#endif

constexpr bool test() {
  { // ==
    decltype(auto) result = std::nullopt == std::nullopt;
    static_assert(std::is_same_v<decltype(result), bool>);
    static_assert(noexcept(std::nullopt == std::nullopt));

    assert(result);
  }
  { // !=
    decltype(auto) result = std::nullopt != std::nullopt;
    static_assert(std::is_same_v<decltype(result), bool>);
    static_assert(noexcept(std::nullopt != std::nullopt));

    assert(!result);
  }
  { // <=
    decltype(auto) result = std::nullopt <= std::nullopt;
    static_assert(std::is_same_v<decltype(result), bool>);
    static_assert(noexcept(std::nullopt <= std::nullopt));

    assert(result);
  }
  { // >=
    decltype(auto) result = std::nullopt >= std::nullopt;
    static_assert(std::is_same_v<decltype(result), bool>);
    static_assert(noexcept(std::nullopt >= std::nullopt));

    assert(result);
  }
  { // >
    decltype(auto) result = std::nullopt > std::nullopt;
    static_assert(std::is_same_v<decltype(result), bool>);
    static_assert(noexcept(std::nullopt > std::nullopt));

    assert(!(std::nullopt > std::nullopt));
  }
  { // <
    decltype(auto) result = std::nullopt < std::nullopt;
    static_assert(std::is_same_v<decltype(result), bool>);
    static_assert(noexcept(std::nullopt < std::nullopt));

    assert(!result);
  }

#if TEST_STD_VER >= 20
  { // <=>
    std::same_as<std::strong_ordering> decltype(auto) result = std::nullopt <=> std::nullopt;
    static_assert(noexcept(std::nullopt <=> std::nullopt));

    assert(result == std::strong_ordering::equal);
  }

  { // Test ranges::find with nullopt
    std::vector<std::optional<int>> v = {1, 2, std::nullopt, 4, 5};

    auto it = std::ranges::find(v, std::nullopt);

    assert(it != v.end());
    assert(*it == std::nullopt);
  }
#endif

  return true;
}

int main(int, char**) {
  test();
  static_assert(test());

  return 0;
}