Question

I have a class with a protected method Zig::punt() and I only want it to be accessible to the class “Avocado”. In C++, you’ll normally do this using the “friend Avocado” specifier, but this will cause all of the other variables to become accessible to “Avocado” class; I don’t want this because this breaks encapsulation.

Is what I want impossible, or does there already exist an obscure trick out there that I can use to achieve what I want? Or possibly alternative class design patterns that’ll achieve the same thing?

Thanks in advance for any ideas!

Answer 1

Here’s an ugly yet working trick:

class AvocadoFriender {
protected:
  virtual void punt() = 0;
  friend class Avocado; 
}

class Zig : public AvocadoFriender {
  ...
protected:
  void punt();
}

Basically you add a mixin class that exposes only the part of the interface that you want to Avocado. We take advantage of the fact that by inheriting a class that is befriended to Avocado you don’t expose anything more except what was exposed originally.