Overloaded friend Functions
It’s possible to specify overloaded functions as
friends of a class. Each function intended to be a
friend must be explicitly declared in the class definition as a
friend of the class.
Software Engineering Observation 9.12
Even though the prototypes for friend functions appear in the class definition, friends are not member functions.
Software Engineering Observation 9.13
Member access notions of private, protected and public are not relevant to friend declarations, so friend declarations can be placed anywhere ...