CS202   7- ‹#›
Member Function Friends
•But... A member function cannot be declared a friend before it is first declared as a member of its own class.
•Unlike a friend class, where we can have an incomplete declaration, friend member function declarations (in our declaring class) cannot take place until after the member functions have been declared (in their own class).
•If two or more classes share the same friend class or function, those classes share a mutual friend. This means that more than one class gives a single friend class or function permission to access their members.