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From: "redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/56760] namespaces, templates and forwarding declarations.
Date: Thu, 28 Mar 2013 11:05:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56760

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> 2013-03-28 11:05:26 UTC ---
(In reply to comment #8)
> I read the section on name lookup changes at
> http://gcc.gnu.org/gcc-4.7/porting_to.html
> 
> but it talks about a different kind of problem. Consider that there the
> compiler does error messages. But here at our problem the linker (!) does the
> error.

It's the same problem.  You get a linker error because this line:

  func(containHolder, b); // COMMENT THIS OUT AND IT WORKS

calls this function:

  template<class T> void func(const seco::contain<T> &a, nam::binbuffer &b)
  { func(*a.wombat, b); }

which then calls this function:

  template<class T> void func (const T &a, nam::binbuffer &b);

which is not defined. So you get a linker error.

You are expecting it to call this function:

  template<class T> void func(const seco::holder<T> &a, nam::binbuffer &b)
  { func(*a.fun, b); }

but it cannot, because that is not declared before it is used. This is the
situation described in the name lookup changes.

Your code is not valid C++, the compiler is correct.