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

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std::chrono::year_month_weekday_last
 
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

Run this code
#include <iostream>
#include <chrono>
using namespace std::chrono;
 
int main()
{
    std::cout << std::boolalpha;
 
    constexpr auto ymwdl1 {Tuesday[last]/11/2021};
    auto ymwdl2 = ymwdl1;
    ymwdl2 = months(12) + ymwdl2;
    ymwdl2 = ymwdl2 - years(1);
    std::cout << (ymwdl1 == ymwdl2) << '\n';
}

Output: 

true
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