Three-way Comparison Basics

#include <compare>
#include <iostream>
#include <string>
struct Version {
    int major, minor, patch;
    
    // Spaceship operator - generates all comparison operators!
    auto operator<=>(const Version&) const = default;
};
struct Point {
    double x, y;
    
    // Custom spaceship for specific ordering
    auto operator<=>(const Point& other) const {
        // Compare by distance from origin
        auto dist1 = x*x + y*y;
        auto dist2 = other.x*other.x + other.y*other.y;
        return dist1 <=> dist2;
    }
    
    // Need explicit == when <=> is custom
    bool operator==(const Point& other) const {
        return x == other.x && y == other.y;
    }
};
int main() {
    Version v1{1, 2, 3};
    Version v2{1, 2, 4};
    Version v3{1, 2, 3};
    
    std::cout << std::boolalpha;
    std::cout << "v1 < v2: " << (v1 < v2) << std::endl;   // true
    std::cout << "v1 == v3: " << (v1 == v3) << std::endl; // true
    std::cout << "v2 > v1: " << (v2 > v1) << std::endl;   // true
    
    Point p1{3, 4};   // distance = 5
    Point p2{6, 8};   // distance = 10
    
    std::cout << "p1 < p2: " << (p1 < p2) << std::endl;   // true
    
    return 0;
}