Re: [boost] [TR1/Fusion] Conflict between TR1 and Fusion headers

From: John Maddock (john_at_[hidden])
Date: 2008-03-05 08:56:16

Richard Webb wrote:
> Hi,
> I've got a project that uses Boost.TR1 (by adding boost/tr1/tr1 to my
> include path) and Fusion, and i've run into some errors when
> including the Fusion headers.
> For example:
>
> boost/fusion/tuple/make_tuple.hpp(21) : error C2027: use of undefined
> type 'boost::fusion::tuple<>'
>
> boost/fusion/iterator/prior.hpp(50) : error C2039: 'tag_of' : is not
> a member of 'boost::fusion::detail'
>
> This seems to be caused by the inclusion of <utility> in
> <boost/fusion/support/tag_of.hpp>, which when using Boost.TR1 like
> this causes the Fusion headers to be included again. At the point
> when <utility> is included, the tag_of include guard has been defined
> but tag_of itself hasn't been declared, so nested inclusions of
> tag_of.hpp do nothing and the build fails.
>
> My code builds ok if i either:
> -Include <utility> myself before Fusion
> -Remove the include <utility> from tag_of.hpp (it doesnt actually
> seem to be required - at least, the regression tests all pass with it
> removed)
>
> This seems a bit fragile though. Is there a better way it can be
> fixed?

Hmmm, confirmed that this is an issue with current SVN trunk, this is tricky 
to solve and I can't think of a method in TR1 that would work off hand... 
Joel any ideas if there's an easy (and non-fragile!) way to fix this in 
fusion?

John.