std::chrono:: operator==,<=> (std::chrono::year_month_day)

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chrono I/O
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C-style date and time
std::chrono::year_month_day
Defined in header <chrono>
constexpr bool operator == ( const std:: chrono :: year_month_day & x,
const std:: chrono :: year_month_day & y ) noexcept ;
(1) (since C++20)
(2) (since C++20)

Compares the two year_month_day values x and y . This is a lexicographical comparison: the year() is compared first, then month() , then day() .

The < , <= , > , >= , and != operators are synthesized from operator <=> and operator == respectively.

Return value

1) x. year ( ) == y. year ( ) && x. month ( ) == y. month ( ) && x. day ( ) == y. day ( )
2) If x. year ( ) <=> y. year ! = 0 , x. year ( ) <=> y. year ; otherwise if x. month ( ) <=> y. month ( ) ! = 0 , x. month ( ) <=> y. month ( ) ; otherwise x. day ( ) <=> y. day ( ) .

Notes

If both x and y represent valid dates ( x. ok ( ) && y. ok ( ) == true ), the result of the lexicographical comparison is consistent with the calendar order.

Example

Run this code 
#include <chrono>
 
int main()
{
    constexpr auto ymd1{std::chrono::day(13)/7/1337};
    constexpr auto ymd2{std::chrono::year(1337)/7/13};
    static_assert(ymd1 == ymd2);
    static_assert(ymd1 <= ymd2);
    static_assert(ymd1 >= ymd2);
    static_assert(ymd1 <=> ymd2 == 0);
}
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