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

From cppreference.net
C++
Date and time library
std::chrono::year
定义于头文件 <chrono>
constexpr bool operator == ( const std:: chrono :: year & x,
const std:: chrono :: year & y ) noexcept ;
(1) (C++20 起)
constexpr std:: strong_ordering operator <=> ( const std:: chrono :: year & x,
const std:: chrono :: year & y ) noexcept ;
(2) (C++20 起)

比较两个 std::chrono::year x 与 y 。

< 、 <= 、 > 、 >= 和 != 运算符分别由 operator <=> 和 operator == 合成。

返回值

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

示例

运行此代码 
#include <chrono>
#include <iostream>
int main()
{
    using namespace std::chrono;
    constexpr year y1{2020};
    constexpr year y2{2021};
    std::cout << std::boolalpha << (y1 != y2) << '\n';
    static_assert((2020y < 2023y) && (2020y == 2020y) && (2020y <= 2023y) &&
                  (2023y > 2020y) && (2023y != 2020y) && (2023y >= 2020y));
}

输出： 

true