Re: class does not want to get friends with another class

[Axel Freyn <axel-freyn at gmx dot de>]

Hi,
> 
> david.hagood wrote:
> > 
> > On Thu, 2010-10-07 at 14:08 -0700, brac37 wrote:
> >> Hello,
> >> 
> >> I have some code that works when I make class classA public. But I only
> >> want
> >> class classA to be accessible by itself and class classB. So the problem
> >> is
> >> very concrete: make classB a friend of classA.
> >> 
> >> Here is the code that describes both classes.
> >> 
> >> 
> >> 
> >> template <class T, int C> class classA;
> >> 
> >> template <class T, int C, classA<T,C> &instanceA> class classB;
> >> 
> >> template <class T, int C> class classA
> >> {
> >> 
> >>   template <classA &instanceA> friend class classB;
> > I think your problem is that you are not fully specifying the template
> > parameters for class B, thus as far as class A is concerned, you are
> > speaking of some other class B.
> > 
> > I think you have to fully spec out class B here:
> > 
> > friend class classB<T,C,classA&>;
> > 
> 
> No, that does not work. This time, the error is given already before
> instantiation. The error is that that the third parameter ClassA & is not of
> the right kind: it is a type instead of a constant instance of that type.
This is the same problem as in your other mail: You try to make a
partial template specialization of classB to be friend of classA. That
won't work (if I understood the C++-Standard correctly in this point...)

What you can do, is to make friend the "complete" template classA:
template <class T1, int C1, classA<T1, C1> &instanceA> friend class classB;

works.


Axel