[Bug c++/13935] [3.4/3.5 Regression] Template friend lookup bug

["gdr at integrable-solutions dot net" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From gdr at integrable-solutions dot net  2004-01-30 19:23 -------
Subject: Re:  [3.4/3.5 Regression] Template friend lookup bug

"giovannibajo at libero dot it" <gcc-bugzilla@gcc.gnu.org> writes:

| ------- Additional Comments From giovannibajo at libero dot it  2004-01-30 17:58 -------
| Well, when I say:
| 
| friend class B;
| 
| I'm saying that ::B is a friend of MainClass<> (and ::B is thus predeclared). 
| Then, I'm defining MainClass<>::B<>, which is a totally unrelated
| type. I don't  see how this could be illegal.

That is the same thing as for

   struct foo { };

   struct bar {
      foo foo;
   };  

The first 'foo' refers to the outer foo, and the second changes the
meaning of the first.  That is ill-formed even though a diagnostic is
not required.  If you want to make that valid construct, then you need
to qualify explicitly

   struct bar {
      ::foo foo;
   };

See 3.3.6/1
   [...]
   2) A name N used in a class S shall refer to the same declaration
      in its context and when reevaluated in the completed scope of
      S. No diagnostic is required for a violation of this rule.

| I think the crucial point is about this:
| template < class TP2 > friend class B;
| 
| Does this refer to ::B or to MainClass<>::B<>?

That refers to the second, but then the meaning of the use of the
unqualified name 'B' changes after the class is completed.

| How is the lookup performed, exactly? 

On the first friend declaration, one looks into the current class
scope, finds nothing, then looks into the enclosing namespace scope.
One finds ::B.  But when MainClass<> is completed, you see that the
meaning of B (as en unqualified name in the scope of MainClass<>) has
changed. So, your program is in error.

-- Gaby


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13935