test/std/utilities/time/time.cal/time.cal.ymd/time.cal.ymd.members/plus_minus_equal_month.pass.cpp

//===----------------------------------------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is dual licensed under the MIT and the University of Illinois Open
// Source Licenses. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
// UNSUPPORTED: c++03, c++11, c++14, c++17

// <chrono>
// class year_month_day;

// constexpr year_month_day& operator+=(const months& m) noexcept;
// constexpr year_month_day& operator-=(const months& m) noexcept;

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

#include "test_macros.h"

template <typename D, typename Ds>
constexpr bool testConstexpr(D d1)
{
    if (static_cast<unsigned>((d1          ).month()) !=  1) return false;
    if (static_cast<unsigned>((d1 += Ds{ 1}).month()) !=  2) return false;
    if (static_cast<unsigned>((d1 += Ds{ 2}).month()) !=  4) return false;
    if (static_cast<unsigned>((d1 += Ds{12}).month()) !=  4) return false;
    if (static_cast<unsigned>((d1 -= Ds{ 1}).month()) !=  3) return false;
    if (static_cast<unsigned>((d1 -= Ds{ 2}).month()) !=  1) return false;
    if (static_cast<unsigned>((d1 -= Ds{12}).month()) !=  1) return false;
    return true;
}

int main()
{
    using year           = std::chrono::year;
    using month          = std::chrono::month;
    using day            = std::chrono::day;
    using year_month_day = std::chrono::year_month_day;
    using months         = std::chrono::months;

    ASSERT_NOEXCEPT(std::declval<year_month_day&>() += std::declval<months>());
    ASSERT_NOEXCEPT(std::declval<year_month_day&>() -= std::declval<months>());

    ASSERT_SAME_TYPE(year_month_day&, decltype(std::declval<year_month_day&>() += std::declval<months>()));
    ASSERT_SAME_TYPE(year_month_day&, decltype(std::declval<year_month_day&>() -= std::declval<months>()));
    
    static_assert(testConstexpr<year_month_day, months>(year_month_day{year{1234}, month{1}, day{1}}), "");

    for (unsigned i = 0; i <= 10; ++i)
    {
        year y{1234};
        day   d{23};
        year_month_day ym(y, month{i}, d);
        assert(static_cast<unsigned>((ym += months{2}).month()) == i + 2);
        assert(ym.year() == y);
        assert(ym.day()  == d);
        assert(static_cast<unsigned>((ym             ).month()) == i + 2);
        assert(ym.year() == y);
        assert(ym.day()  == d);
        assert(static_cast<unsigned>((ym -= months{1}).month()) == i + 1);
        assert(ym.year() == y);
        assert(ym.day()  == d);
        assert(static_cast<unsigned>((ym             ).month()) == i + 1);
        assert(ym.year() == y);
        assert(ym.day()  == d);
    }
}