Operator Overloading in struct

Question

Suppose I define this structure:

struct Point {
   double x, y;
};

How can I overload the + operator so that, declared,

Answer 1

In C++ there's only one difference between a struct and a class: in a struct the default visibility is public while in a class it is private.

Other than that you can do anything you would do in a class in a struct and it will look exactly the same.

Write operator overloading in a struct as you would in a class.

Answer 2

Just do it:

Point operator+( Point const& lhs, Point const& rhs );
Point operator+( Point const& lhs, double rhs );
Point operator+( double lhs, Point const& rhs );

With regards to your last question, the compiler makes no assumptions concerning what your operator does. (Remember, the + operator on std::string is not commutative.) So you have to provide both overloads.

Alternatively, you can provide an implicit conversion of double to Point (by having a converting constructor in Point). In that case, the first overload above will handle all three cases.

Answer 3

This will also work:

struct Point{
    double x,y;
    Point& operator+(const Point& rhs){ 
            x += rhs.x;
            y += rhs.y;
            return *this;
    }
}

Answer 4

Here is how I would do it.

struct Point {
   double x, y;
   struct Point& operator+=(const Point& rhs) { x += rhs.x; y += rhs.y; return *this; }
   struct Point& operator+=(const double& k) { x += k; y += k; return *this; }
};

Point operator+(Point lhs, const Point& rhs) { return lhs += rhs; }
Point operator+(Point lhs, const double k) { return lhs += k; }
Point operator+(const double k, Point rhs) { return rhs += k; }