[Bug c++/45942] class will not get friends with another class

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45942

--- Comment #6 from Jonathan Wakely <redi at gcc dot gnu.org> 2010-10-08 15:08:36 UTC ---
(In reply to comment #4)
> (In reply to comment #2)
> > This code is not valid, G++ is correct to reject it.
> 
> Please explain why the code is invalid, and do not click "Resolved invalid"
> until ClassB is a friend of ClassA.

You reported an invalid bug, so I rejected it.
It's not my job to teach you C++ but here you go:

template <class T, int C> class A;

template <class T, int C, A<T,C> &a> class B;

template <class T, int C> class A
{
  template <class X, int Y, A<X,Y>&> friend class B;
};


That makes B<X,Y,A<X,Y>&> a friend of A

Your original example is invalid for the reason the compiler gave, the syntax
you tried to use declares a partial specialization, which is not allowed in a
friend declaration.  That's how C++ works, I don't make the rules.