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

From cppreference.net
C++
Date and time library
std::chrono::year_month
Definido en el encabezado <chrono>
constexpr bool operator == ( const std:: chrono :: year_month & x,
const std:: chrono :: year_month & y ) noexcept ;
(1) (desde C++20)
constexpr std:: strong_ordering operator <=> ( const std:: chrono :: year_month & x,
const std:: chrono :: year_month & y ) noexcept ;
(2) (desde C++20)

Compara los dos valores year_month x y y .

Los operadores < , <= , > , >= y != se sintetizan a partir de operator <=> y operator == respectivamente.

Valor de retorno

1) x. year ( ) == y. year ( ) && x. month ( ) == y. month ( )
2) x. year ( ) <=> y. year ( ) ! = 0 ? x. year ( ) <=> y. year ( ) : x. month ( ) <=> y. month ( )

Ejemplo

Ejecutar este código 
#include <chrono>
#include <iostream>
int main()
{
    using namespace std::chrono;
    constexpr year_month ym1{year(2021), month(7)};
    constexpr year_month ym2{year(2021)/7};
    static_assert(ym1 == ym2);
    std::cout << ym1 << '\n';
    static_assert((2020y/1 < 2020y/2) && (2020y/2 == 2020y/2) && (2020y/3 <= 2021y/3) &&
                  (2023y/1 > 2020y/2) && (3020y/2 != 2020y/2) && (2020y/3 >= 2020y/3));
}

Salida: 

2021/Jul