185. Friend Function

Question.2

A developer needs int + Vec to work (not just Vec + int):

class Vec {
   int x;
public:
   Vec(int v) : x(v) {}
   friend Vec operator+(int n, const Vec& v) {
       return Vec(n + v.x);
   }
};

Vec a(10);
Vec b = 5 + a;  // int on the LEFT

Why must operator+ be a friend instead of a member?

Need Help? Refer to the Quick Guide below

Friend functions are faster for operators
A member operator+ requires the class object on the left (this); for int + Vec, int is on the left -- a free function is needed, and friend gives it access to the private member x
The compiler requires friend for all binary operators
Member operators cannot return objects

Restart quiz!