std::chrono::operator+, std::chrono::operator- (std::chrono::year_month_weekday_last)

From cppreference.com
 
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
 
 
constexpr std::chrono::year_month_weekday_last

    operator+( const std::chrono::year_month_weekday_last& ymwdl,

               const std::chrono::months& dm ) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

    operator+( const std::chrono::months& dm,

               const std::chrono::year_month_weekday_last& ymwdl ) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

    operator+( const std::chrono::year_month_weekday_last& ymwdl,

               const std::chrono::years& dy ) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

    operator+( const std::chrono::years& dy,

               const std::chrono::year_month_weekday_last& ymwdl ) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

    operator-( const std::chrono::year_month_weekday_last& ymwdl,

               const std::chrono::months& dm ) noexcept;
(since C++20)
constexpr std::chrono::year_month_weekday_last

    operator-( const std::chrono::year_month_weekday_last& ymwdl,

               const std::chrono::years& dy ) noexcept;
(since C++20)
1,2) Adds dm.count() months to the date represented by ymwdl. The result has the same year() and month() as std::chrono::year_month(ymwdl.year(), ymwdl.month()) + dm and the same weekday() as ymwdl.
3,4) Adds dy.count() years to the date represented by ymwdl. The result is equivalent to std::chrono::year_month_weekday_last(ymwdl.year() + dy, ymwdl.month(), ymwd.weekday_last()).
5) Subtracts dm.count() months from the date represented by ymwdl. Equivalent to ymwdl + -dm.
6) Subtracts dy.count() years from the date represented by ymwdl. Equivalent to ymwdl + -dy.

For durations that are convertible to both std::chrono::years and std::chrono::months, the years overloads (3,4,6) are preferred if the call would otherwise be ambiguous.

Example

#include <cassert>
#include <chrono>
using namespace std::chrono;
 
int main()
{
    constexpr auto ymwdl1{Tuesday[last]/11/2021};
    auto ymwdl2 = ymwdl1;
    ymwdl2 = std::chrono::months(12) + ymwdl2;
    ymwdl2 = ymwdl2 - std::chrono::years(1);
    assert(ymwdl1 == ymwdl2);
}