Is there a way in C++ to render a class' interface private to all classes except a few?

Question

I am writing a B-link tree and its attendant sub classes like a data page class and a node class etc.

I was wondering is there a way to protect the public interfaces of the nodes and pages such that only the b-link tree class itself can access them, WITHOUT simultaneously exposing the private methods of the pages and nodes to the b-link class?

IE I have already thought of simply changing the 'public' interface of the pages and nodes into the protected category and then declaring the B-link tree as a friend but that gives the b-link tree access to private methods that I want to stay private.

Answer 1

Off the top of my head, you could do something like:

class FooAdapter;

class Foo
{
private:
     void funcToExpose();
     void funcToHide();
     friend FooAdapter;
};

class FooAdapter
{
private:
     Foo foo;
     void funcToExpose() { foo.funcToExpose(); }

     friend SomeFriend;
};

(Not compiled or tested, but you should get the idea.)

Answer 2

If you don't want the interfaces of the nodes and pages to be exposed in your API then just declare them inside your b-link implementation file. If the b-link implementation spans more than one file, then put the node and page class declarations in an implementation-only header file (co-located with your implementation files, not with your API headers).

Answer 3

You can try defining your attendant sub classes in an anonymous namespace in the same translation unit as the b-tree. Supposedly that will make those clases inaccesible from outside that translation unit.

See http://stackoverflow.com/questions/154469/unnamed-anonymous-namespaces-vs-static-functions