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

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.