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

From cppreference.net
< cpp ‎ | chrono ‎ | day
C++
Date and time library
std::chrono::day
Defined in header <chrono>
constexpr bool operator == ( const std:: chrono :: day & x,
const std:: chrono :: day & y ) noexcept ;
(1) (since C++20)
constexpr std:: strong_ordering operator <=> ( const std:: chrono :: day & x,
const std:: chrono :: day & y ) noexcept ;
(2) (since C++20)

Compare the two std::chrono::day x and y .

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

Return value

1) unsigned ( x ) == unsigned ( y )
2) unsigned ( x ) <=> unsigned ( y )

Example

Run this code 
#include <chrono>
#include <iostream>
int main()
{
    constexpr std::chrono::day x{13}, y{31};
    static_assert(x != y);
    if constexpr (constexpr auto res = x <=> y; res < 0)
        std::cout << "x is less than y\n";
    else if constexpr (res > 0)
        std::cout << "x is greater than y\n";
    else
        std::cout << "x and y are equal\n";
    using namespace std::literals::chrono_literals;
    static_assert
    (
        (6d < 9d) && (6d == 6d) && (6d <= 9d) &&
        (9d > 6d) && (9d != 6d) && (9d >= 6d)
    );
}

Output: 

x is less than y