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ban of inheritance

ML380 (8)
Hi!
I have found question: How do I forbid opportunity of inheritance, using virtual inheritance?
I thought that it's impossible in C++.
quirkyusername (792)
Like so:

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class Unoverloadable;

class Base
{
    private:
        friend Unoverloadable;
        Base(){}
};

class Unoverloadable : public virtual Base
{
    // class definition
};


now since derived classes need access to their base class constructors, and only Unoverloadable can access Base as its constructor is private, nothing can be derived from Unoverloadable.

May I ask why exactly you want to prevent inheritance?
quirkyusername (792)
Does anyone know if C++ is getting a final keyword like java in C++ 0x? Or for that matter anything else interesting that's coming to 0x
Last edited on
Moschops (7244)
I know auto is coming (as Stroustrup intended way back in the mists of time when he started all this, apparently). I don't know if I'd call it interesting; I've never really minded having to declare a type when I create an object.
quirkyusername (792)
Never heard of auto but I looked it up and to me it just makes things less readable =/
filipe (1165)
Not necessarily. What's the most readable version:

for(auto it = vec.begin(); it != vec.end(); ++it)

or

for(std::vector<std::vector<MyClass> >::iterator it = vec.begin(); it != vec.end(); ++it)

?
Albatross (4553)
Although I haven't heard of a "final" keyword for C++, I would be really disappointed if it was implemented. That's a feature of Java that I really didn't like. Can't we point guns at our feet when we want to?

-Albatross
firedraco (6243)
Tbh, final is dumb. Who are you to say that no-one should be able to derive from your class?
Seraphimsan (954)
the original author. (hence the owner of the intellectual property of the code)
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Albatross (4553)
I'd have liked to keep restrictions on the uses of individual pieces of code and tiny sub-sections of a library out of open source software.

-Albatross
Seraphimsan (954)
Doesn't have to be open source. Could be closed source with an interface for the library. Don't get me wrong I'm all for the current c++ philosophy and completely unrestricted code. Just playing the devils advocate here.
Albatross (4553)
Just playing the devils advocate here.

Where's my holy water? I need to sprinkle some on the seraph. ;)

I'm pretty sure Java has a keyword for creating interfaces separate from the implementations, but I haven't touched the language in so long I almost forgot.

-Albatross
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rocketboy9000 (562)
auto... I already sorta made something like that:
#define let(x,y) typeof(y) x=y
Also, if you don't want people to inherit, why not just do this:
class Foo{//If you inherit, I'll hunt you down and eat your soul
(Using whatever threat you can get away with, obviously.)
firedraco (6243)
@Albatross: It does. It's basically a class with only (pure?) virtual functions. Since Java doesn't support multiple inheritance it's the only way to do some things in it.
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ML380 (8)
May I ask why exactly you want to prevent inheritance?

I haven’t any desire to do that. It’s only theoretical question. I have found it in one questions list for test C++ knowledge, and can’t get answer.
ML380 (8)
By the way, another theoretical question.
In Java, keyword ‘final’ also can prevent the redefining of method. Is there any trick in C++ to do the same?
m4ster r0shi (2201)
This works for me, but I don't know if it's portable.

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template <class T>
struct FriendMaker { typedef T Type; };

template <class T>
class Uninheritable
{
    //compiler bug \/
    friend class FriendMaker<T>::Type;
    ~Uninheritable(){}
};

class NotABase: virtual public Uninheritable<NotABase> {};
class NotADerived: public NotABase {};

int main()
{
    NotABase a;

    //uncommenting any of the following statements
    //results in a compilation error

    //NotADerived b;
    //NotADerived * pb=new NotADerived;
    //NotABase * pa=new NotADerived;

    return 0;
}

EDIT: Forgot to put the virtual keyword there...
It forces NotADerived to call the Uninheritable<NotABase> dtor, which causes an error.
Last edited on
ML380 (8)
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//compiler bug \/
friend class FriendMaker<T>::Type;

In Visual Studio you can use the
Friend T;
Without using of auxiliary FriendMaker.
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