Re: [boost] Code question on fusion tag_of.hpp

Subject: Re: [boost] Code question on fusion tag_of.hpp
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2012-08-09 04:10:21

On 08/08/2012 23:39, Dave Steffen wrote:
> Hi Folks
>
> During a recent bug hunt, we came across the following (Boost 1.49,
> fusion/adapted/std_tuple/tag_of.hpp):
>
> #include <tuple>
>
> namespace std
> {
>      template <typename... Elements>
>      class tuple;
> }
>
> We find this rather puzzling -- why is this here?  As far as we can
> tell, this doesn't do anything.

It forward declares std::tuple so that it can specialize its traits for it.

But it really shouldn't do that, since there is no guarantee this 
declaration is compatible with the standard one.