Inheritance type forcing

Question

Is it possible to make inheritance forced to be public, private or protected?

Ie:

class block: public shape{ // Only way to inherit from shape
};

// class block: private shape{}; // throws an error

To make things more clear:

• this will not cause an error in its current state
• What I want to achieve is to enforce the constraint where any class that derives from shape be public. eg. If a class tries to privately inherit from shape that should trigger a compile error.

Answer 1

There is generally no way that a base can dictate the interfaces of its derived classes. Such constraint doesn't seem to solve any problem, and "forced publicity" could easily be worked around by restricting access to the derived class.

For example, Square here provides a public interface to Shape, but nobody can access Square anyway due to access protection.

class SquaresAreAllMine {
private:
    class Square : public Shape {};
};

(Declaring signatures of virtual functions is an exception, as there is no way for a derived class to revert to non-virtual status. This is not really intended to be restrictive, though.)