Invisible <voi### [at] devnull> wrote:
> > class X; // declaration of X

> Ah, I see. This is the fact I was looking for. :-)

> So this does... what? Tells the compiler "hey, this type exists, but I'm 
> not going to tell you anything about it"?

  It tells that there's a class named X.

  From that point forward you can do anything with that type that does not
require calling its member functions or accessing its contents. (In other
words, you can handle pointers and references of that type.) You can also
make further declarations using it (such as declaring it as the return
type of a function).

  Doing anything else with an object of that type requires a full class
definition, but that can be done later in the code.

  This allows inter-dependency between classes.

> >>> (For obvious reasons. It would be an infinitely large class.)
> >
> >> It can if at least one of the classes refers to the other through a
> >> pointer or a reference.
> >
> >    It wouldn't be a member variable then.

> What would it be then?

  A pointer/reference to an object of that type.

  What I mean is that you can't do this:

class A { B b; };
class B { A a; };

  That would be a pair of infinitely large classes.

-- 
                                                          - Warp

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