how to overload operator == outside template class using friend function?

Question

I\'m trying to write a template class which overloads operator==. I know how to get it inside the class:

    template 
            


        

Answer 1

@Kühl's answer is the most permissive approach to declare a templated friend function of a templated class. However, there is one unapparent side effect of this approach: All template instantiations of Point are friends with all template instantiations of operator==(). An alternative is to make only the instantiation with the same type of Point a friend. Which is done by adding a in the friend declaration of operator==().

template  class Point;

template 
bool operator== (Point, Point);

template 
class Point {
    // ...
    friend bool operator== (Point, Point);
};

References
http://web.mst.edu/~nmjxv3/articles/templates.html