CODEWITHSUNDEEP
c++c++11inheritance
Exagon
Exagon

Reputation: 5098

Only inherit one time from a class

I have a class A and I need a subclass of A class B: public A. How can I achieve that I can inherit from this class but nobody else ever can inherit again from this two classes? If i make class A final B can't inherit from A.

Upvotes: 1

Views: 268

Answers (3)

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

Just an idea (though I don't think that's actually a good design):

class B;
class A {
     // everything's private
     friend class B; // << except for class B
};

class B final // << final prevents from further inheritance
: A {
     public:
     // What you want to publish ...
};

Though as mentioned before, I don't see that much point for class A unless you want to have more class instantiations like class B.

Upvotes: 2

Nicol Bolas
Nicol Bolas

Reputation: 474406

There is no way in C++ to say that only one class can inherit from another class. Either a class is final (and thus uninheritable) or it isn't.

The absolute best you could do is have A declare its constructors private and make B a friend of A. But that would make it difficult for other users to create objects of type A.

Upvotes: 6

David
David

Reputation: 28178

As I commented: I'm unclear on what you want. You want B to be able to inherit from A, but no new classes to ever be able to inherit from either? Going on that assumption your best bet is to make A's ctor private and friend B, while making B final.

I don't know what you're after, design wise, but this is bad design. It does, however, answer your question.

Upvotes: 2

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