Conversions in a chain of classes

Question

I have an object S. S is composed of layers S0, S1, S2 ... just like a stack of stackable drawers.

I want to create a chain of template classes A, B, C such that:

1. They represents proxies to different layers of the S object.
2. Even during template instantiation, C can convert to B, which can convert to A.
3. A, B, and C have different sets of methods.

The problem is that if I use public inheritance, then C will get the methods of A and B.

Test:

#include <iostream>
// Library
template <typename T>
class A {
public:
    void a() {std::cout << "a\n"; }
    int s_{0};
};

template <typename T>
class B : public A<T> {
public:
    void b() {std::cout << "b\n"; }
};

template <typename T>
class C : public B<T> {
public:
    void c() {std::cout << "c\n"; }
};

// User of library write a function like this
template <typename T>
void foo(A<T>& a) { a.a(); }

// The problem:
int main() {
    C<int> c;
    foo(c);
    c.a();  // <--- how to hide this?
    return 0;
}

Answer 1

I'm not sure if I understand what you want. But one way to do it is changing the access level of base class member in derived class. For example:

template <typename T>
class C : public B<T> {
public:
    void c() { std::cout << "c\n"; }
private:
    using A::a;  // <-- reduce access level of base class member
};