Method toString

tests/test_operator_overloading.cpp:41–43

    ~Vector2() { print_destroyed(this); }

    std::string toString() const {
        return "[" + std::to_string(x) + ", " + std::to_string(y) + "]";
    }

    Vector2 operator-() const { return Vector2(-x, -y); }
    Vector2 operator+(const Vector2 &v) const { return Vector2(x + v.x, y + v.y); }