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

Subject: Re: [boost] Code question on fusion tag_of.hpp
From: Dave Steffen (dave.steffen_at_[hidden])
Date: 2012-08-09 12:04:05

Mathias Gaunard wrote:
 > 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.

Well, first of all, it's not a forward declaration, right?  std::tuple 
is declared in whatever gets included with #include<tuple>, right?  So 
it's not a forward declaration, it's a... what?  A backwards 
declaration? :-)  It's redundant at any rate.  (Or I'm completely wrong, 
in which case I'm missing something.)

And then, yes, this may or may not be compatible with the real 
std::tuple (which is what we were looking in to when we found this).

-- 
Dave Steffen
Software Engineer
NUMERICA CORPORATION
www.numerica.us
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