ban of inheritance

[ML380]

Hi!
I have found question: How do I forbid opportunity of inheritance, using virtual inheritance?
I thought that it's impossible in C++.

[quirkyusername]

Like so:

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]

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

[Moschops]

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]

Never heard of auto but I looked it up and to me it just makes things less readable =/

[filipe]

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]

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]

Tbh, final is dumb. Who are you to say that no-one should be able to derive from your class?

[Seraphimsan]

the original author. (hence the owner of the intellectual property of the code)

[Albatross]

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]

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]

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

[rocketboy9000]

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]

@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.

[ML380]

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]

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]

This works for me, but I don't know if it's portable.

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.

[ML380]

//compiler bug \/
friend class FriendMaker<T>::Type;

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