[Bug libstdc++/14926] [3.4/3.5 regression] forward declarations and strong using

[llewelly@xmission.com]

"bangerth at dealii dot org" <gcc-bugzilla@gcc.gnu.org> writes:

> ------- Additional Comments From bangerth at dealii dot org  2004-04-12 20:00 -------
> I was under the impression that an implementation was allowed to declare 
> (for example) its vector class as 
>   template <typename T, typename Allocator = alloc<something>, 
>             typename additional_parameter=something > 
>   class vector {...}; 
> and that this was the reason to make forward declarations of classes in 
> namespace std:: undefined. I may be wrong, though. It doesn't also matter 
> here. 

http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-closed.html#94
explains why additional template parameters are not allowed.