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

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std::chrono::day
 
在标头 <chrono> 定义 
constexpr bool operator==( const std::chrono::day& x,
                           const std::chrono::day& y ) noexcept;
(1) (C++20 起) 
constexpr std::strong_ordering operator<=>( const std::chrono::day& x,
                                            const std::chrono::day& y ) noexcept;
(2) (C++20 起)

比较两个 std::chrono::day x 和 y。

<、<=、>、>= 及 != 运算符分别从 operator<=> 与 operator== 合成。

返回值

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

示例

运行此代码
#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)
    );
}

输出： 

x is less than y