C++怎么使用C++20的Three-Way Comparison(宇宙飞船运算符)_C++代码简化与

#include <iostream>
#include <compare>

struct Point {
    int x;
    int y;

    // 自动生成三路比较
    auto operator<=>(const Point&) const = default;
};

int main() {
    Point a{1, 2};
    Point b{1, 3};

    if (a < b) std::cout << "a < b\n";        // 输出
    if (a != b) std::cout << "a != b\n";      // 输出
    if (a <= b) std::cout << "a <= b\n";      // 输出

    return 0;
}
  

struct Person {
    std::string name;
    int age;

    auto operator<=>(const Person& other) const {
        if (auto cmp = name <=> other.name; cmp != 0)
            return cmp;
        return age <=> other.age;
    }
};
  

struct A { int value; };
struct B { int value; };

auto operator<=>(const A& a, const B& b) {
    return a.value <=> b.value;
}

A a{5};
B b{10};
if (a < b) std::cout << "a < b\n";  // 成立
  

struct Vec3 {
    double x, y, z;
    bool operator==(const Vec3&) const = default;
};