test/std/time/time.cal/time.cal.month/time.cal.month.nonmembers/minus.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
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++03, c++11, c++14, c++17

// <chrono>
// class month;

// constexpr month operator-(const month& x, const months& y) noexcept;
//   Returns: x + -y.
//
// constexpr months operator-(const month& x, const month& y) noexcept;
//   Returns: If x.ok() == true and y.ok() == true, returns a value m in the range
//   [months{0}, months{11}] satisfying y + m == x.
//   Otherwise the value returned is unspecified.
//   [Example: January - February == months{11}. -end example]

#include <chrono>
#include <type_traits>
#include <cassert>

#include "test_macros.h"

using month  = std::chrono::month;
using months = std::chrono::months;

constexpr bool test() {
  month m{6};
  for (unsigned i = 1; i <= 12; ++i) {
    month m1 = m - months{i};
    assert(m1.ok());
    int exp = 6 - i;
    if (exp < 1)
      exp += 12;
    assert(static_cast<unsigned>(m1) == static_cast<unsigned>(exp));
  }

  //  Check the example
  assert(month{1} - month{2} == months{11});

  return true;
}

int main(int, char**) {
  ASSERT_NOEXCEPT(std::declval<month>() - std::declval<months>());
  ASSERT_NOEXCEPT(std::declval<month>() - std::declval<month>());

  ASSERT_SAME_TYPE(month, decltype(std::declval<month>() - std::declval<months>()));
  ASSERT_SAME_TYPE(months, decltype(std::declval<month>() - std::declval<month>()));

  test();
  static_assert(test());

  return 0;
}