README.md

Spaceship (Three-Way Comparison) Operator <=>

Before:

class Point {
public:
  friend bool operator==(const Point& a, const Point& b) { return a.x == b.x && a.y == b.y; }
  friend bool operator< (const Point& a, const Point& b) { return a.x < b.x || (a.x == b.x && a.y < b.y); }
  friend bool operator!=(const Point& a, const Point& b) { return !(a == b); }
  friend bool operator<=(const Point& a, const Point& b) { return !(b < a); }
  friend bool operator> (const Point& a, const Point& b) { return b < a; }
  friend bool operator>=(const Point& a, const Point& b) { return !(a < b); }

private:
  double x, y;
};

Now:

#include <compare>

class Point {
public:
  auto operator<=>(const Point&) const = default;

private:
  double x, y;
};

Note: <compare> header is responsible for populating the compiler with all of the comparison category types necessary for the spaceship operator to return a type appropriate for our defaulted function.

📎 Standard library types (vector, string, map, set, ...) include support for <=>

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