test/std/time/time.cal/time.cal.month/time.cal.month.nonmembers/plus.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: month(int{x} + y.count()).
//
// constexpr month operator+(const months& x, const month& y) noexcept;
//   Returns:
//     month{modulo(static_cast<long long>(int{x}) + (y.count() - 1), 12) + 1}
//   where modulo(n, 12) computes the remainder of n divided by 12 using Euclidean division.
//   [Note: Given a divisor of 12, Euclidean division truncates towards negative infinity
//   and always produces a remainder in the range of [0, 11].
//   Assuming no overflow in the signed summation, this operation results in a month
//   holding a value in the range [1, 12] even if !x.ok(). -end note]
//   [Example: February + months{11} == January. -end example]

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

#include "test_macros.h"

constexpr bool test() {
  using month  = std::chrono::month;
  using months = std::chrono::months;

  month my{2};
  for (unsigned i = 0; i <= 15; ++i) {
    month m1 = my + months{i};
    month m2 = months{i} + my;
    assert(m1.ok());
    assert(m2.ok());
    assert(m1 == m2);
    unsigned exp = i + 2;
    while (exp > 12)
      exp -= 12;
    assert(static_cast<unsigned>(m1) == exp);
    assert(static_cast<unsigned>(m2) == exp);
  }

  return true;
}

int main(int, char**) {
  using month  = std::chrono::month;
  using months = std::chrono::months;

  ASSERT_NOEXCEPT(std::declval<month>() + std::declval<months>());
  ASSERT_NOEXCEPT(std::declval<months>() + std::declval<month>());

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

  test();
  static_assert(test());

  return 0;
}