Lesson 21: Operator Overloading

Operator Overloading\n\nC++ lets you give existing operators new meaning for your own types, making them behave like built‑in types. Overloadable operators include arithmetic, comparison, subscript, function call, and stream insertion/extraction.\n\n---\n\n## Example: Vector2D with arithmetic and stream operators\ncpp\nclass Vector2D {\n double x_, y_;\npublic:\n Vector2D(double x = 0, double y = 0) : x_(x), y_(y) {}\n // addition\n Vector2D operator+(const Vector2D& rhs) const {\n return Vector2D(x_ + rhs.x_, y_ + rhs.y_);\n }\n // scalar multiplication (member)\n Vector2D operator*(double scalar) const {\n return Vector2D(x_ * scalar, y_ * scalar);\n }\n // stream insertion for printing\n friend std::ostream& operator<<(std::ostream& os, const Vector2D& v) {\n return os << '(' << v.x_ << ", " << v.y_ << ')';\n }\n};\n\nint main() {\n Vector2D a{1, 2}, b{3, 4};\n Vector2D c = a + b * 2.0; // uses overloaded * and +\n std::cout << \"c = \" << c << '\\n';\n return 0;\n}\n\n\nKey guidelines:\n- Prefer non‑member overloads for symmetric operators (+, ==).\n- Never overload operators in a way that breaks expected precedence or associativity.\n- Keep overloads intuitive; avoid surprising side‑effects.\n\n> Tip: Overload operator= and the copy/move constructors together to maintain the rule of three/five.\n\n---\n\n<Alert type="warning">You cannot overload &&, ||, , (comma), or ?:.