Operators, Overloading & Spaceship Operator (<=> in C++20)

1Concept

C++ allows user-defined operator overloading. C++20 introduced the Three-Way Comparison (Spaceship) operator <=>, which allows the compiler to auto-generate all 6 relational operators (==, !=, <, <=, >, >=) with default ordering.

2Architecture Diagram

a <=> b:
 Returns:
   - std::strong_ordering::less    (if a < b)
   - std::strong_ordering::equal   (if a == b)
   - std::strong_ordering::greater (if a > b)

3Code Example

#include <iostream>
#include <compare>

struct Point {
    int x;
    int y;

    // C++20 spaceship operator auto-generates ==, !=, <, <=, >, >=
    auto operator<=>(const Point&) const = default;
};

int main() {
    Point p1{10, 20};
    Point p2{10, 30};
    Point p3{10, 20};

    std::cout << std::boolalpha;
    std::cout << "p1 == p3: " << (p1 == p3) << "\n";
    std::cout << "p1 < p2: " << (p1 < p2) << "\n";
    std::cout << "p2 > p1: " << (p2 > p1) << "\n";

    return 0;
}

4Expected Output

p1 == p3: true
p1 < p2: true
p2 > p1: true

5Key Takeaways

• ✓C++20 auto operator<=>(const T&) const = default generates complete ordering comparisons.
• ✓Operator overloading should follow natural mathematical semantics.
• ✓Logical operators && and || short-circuit; overloaded && does not short-circuit.