Consider this:

 class X;

 class Y {
  class X {};
  friend class ::X;  // error!!!
 };

I meet that nice problem when compiling the following code:

 class A {
  class B {};
  friend class A::B;  // error!!!
 };

Most compilers compile this without a warning. Only the one from
DEC produced an 'invalid declarator' error.

I watched the ARM and found out:
 Section 11.4: "... All the functions of a class X can be
  made friends of a class Y by a single declaration
  using an 'elaborated-type-specifier' ('9.1):

   class Y {
    friend class X;
    // ...
   };"

 'elaborated-type-specifier':
  'class-key' 'class-name'
  'class-key' 'identifier'
  enum 'enum-name'

 'class-key':
  class
  struct
  union

 'class-name':
  'identifier'

In what follows: The examples above are really errors!
Correcting the second example is easy:

 class A {
  class B {};
  friend class B;
 };

But how about the first example?!?!?!?

 class X;

 class Y {
  class X {};
  friend class X;  // That's not what I want!
 class X;

Or:

 class X;

 class Y {
  friend class X;  // Error: violating the rewriting rules!
  class X {};
 };

Bye.
Tilo Koerbs,  mkt@uni-jena.de
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