Fine grained access specifiers c++

Question

I have the following class :-

class A {
  public:
    // some stuff that everyone should see
  protected:
    // some stuff that derived classes should see
  private:
    // some stuff that only I can see
    void f();
    void g();
};

Now, I want f() to only be accessible from a certain set of classes (say classes B,C,D) and g() to be accessible from a certain other set of classes (say classes D,E,F). Is there any way to specify this in C++? If I make all the classes friends of A, then both f & g will be accessible from B,C,D,E,F (along with the other private members of A) which is not what I want.

Is this possible or should I change my object model?

Answer 1

class A_f {
    friend class B;
    void f();
};

class A_g {
    friend class C;
    void g();
};

class A: public A_f, public A_g {
    friend class A_f;
    friend class A_g;
private:
    void do_f();
    void do_g();
};

inline void A_f::f() { static_cast<A *>(this)->do_f(); }
inline void A_g::g() { static_cast<A *>(this)->do_g(); }

void B::something(A *a) {
    a->f();
}