[Bug c++/48948] [C++0x] constexpr friend function cannot be defined in-class

[schaub.johannes at googlemail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48948

--- Comment #5 from Johannes Schaub <schaub.johannes at googlemail dot com> 2011-05-10 17:07:30 UTC ---
(In reply to comment #4)
> (In reply to comment #0)
> > gcc 4.7.0 20110507 (experimental) in C++0x mode rejects the following code at
> > the line marked with #:
> > 
> > //---
> > struct B {
> >   friend constexpr int f(B) { return 0; } // #
> > };
> > //---
> > 
> > "error: invalid type for parameter 1 of constexpr function 'constexpr int
> > f(B)'"
> > 
> > This code should be accepted. 
> > 
> 
> I remember that Gaby (I hope I remember correctly, hehe) argued that the body
> of "f" is late-parsed. Hence, the argument, until after the end of definition
> of "B", "f" is only considered declared but not defined.
> 

Consider also this, which I think demonstrates that position:

struct A {
  struct B;
  void f(B) { }
  struct B { };
};

I think this is ill-formed by the spec, because "B" is incomplete in f's
parameter and f is defined at that point. And this is not one of the contexts
that B is allowed to be incomplete by 8.3.5p9.

However, clang, gcc and comeau online all accept this. Apparently, they
consider "f" only declared and not defined.

I would be glad if someone points me to the rule that says that "f" is only
considered defined at the closing "}" of A though.