Re: [boost] Concept check and __LINE__

Subject: Re: [boost] Concept check and __LINE__
From: Kenny Riddile (kfriddile_at_[hidden])
Date: 2010-04-27 17:16:55

Matthew L. Creech wrote:
> I made some trivial changes in a header file today, and suddenly it
> refused to compile, throwing out boost::concept_check errors.  Here's
> an example error:
> 
> In file included from
> /home/mlcreech/work/PCM-tk/etn_export/include/translator++.hpp:193,
>                  from ../../common/source/main.cpp:8:
> /home/mlcreech/work/PCM-tk/etn_export/include/translator/handle.hpp:119:
> error: conflicting declaration ‘typedef struct
> boost::concept::detail::instantiate<boost::concept::requirement<Model>::failed
> [with Model = toolkit::translator::Callable<toolkit::translator::CHandle<toolkit::translator::CValArray<toolkit::translator::CSimpleVal<double>
>>>> ]> toolkit::translator::boost_concept_check119’
> /home/mlcreech/work/PCM-tk/etn_export/include/translator/concept/translatable_archetype.hpp:119:
> error: ‘toolkit::translator::boost_concept_check119’ has a previous
> declaration as ‘typedef struct
> boost::concept::detail::instantiate<boost::concept::requirement<Model>::failed
> [with Model = toolkit::translator::Translatable<toolkit::translator::translatable_archetype<boost::null_archetype<int>
>>> ]> toolkit::translator::boost_concept_check119’
> make[3]: *** [translate++] Error 1
> 
> I had no idea what this was about, but then I went to look up where
> the supposed conflicts were and noticed that they were both on line
> 119.  As it turns out, I have 2 different header files which have
> BOOST_CONCEPT_ASSERT() for different concepts at line 119.  It seems
> that Boost internally generates some global names based on the line
> number, so it creates 2 identially-named enum definitions.  From
> "boost/concept_check/general.hpp":
> 
> #  define BOOST_CONCEPT_ASSERT( ModelInParens )                             \
>   enum { BOOST_PP_CAT(boost_concept_check,__LINE__) =                       \
>          ::boost::concept_check_<void(*) ModelInParens>::instantiate        \
>   }
> 
> Off-hand I'm not sure how to fix this in Boost (maybe some
> preprocessor tricks based on __FILE__?), but it seems like it should
> at least be documented as a limitation.  Or maybe there's some other
> way of using BOOST_CONCEPT_ASSERT() that works around this?
> 
> Obviously the immediate fix is trivial - add a few blank lines.  I
> just thought I'd bring it up in case others hit the same problem.
> Thanks
> 

A similar situation used to exist with the serialization library. 
Perhaps this can be fixed in a similar way?  Here's the old thread:

http://lists.boost.org/Archives/boost/2008/11/145397.php