[boost] ETI bug and iterators

From: Yitzhak Sapir (yitzhak.sapir_at_[hidden])
Date: 2004-08-17 09:01:12

Hello.

I am in the process of upgrading code to use boost 1.31.0 for MSVC6.5.  During this process I happened upon minimum_category.hpp which contains "ETI workarounds".  Now, it seems that the ETI workarounds cause the compilation to fail, with the error message: constant expression expected.  Particularly, we are creating zip iterators to two STLPort vectors.  In debug iterator mode, I get the following error.  (minimum_category.hpp was modified a bit, but the problem is in the instantiation of boost::is_same<T1 or T2,int>).  If I remove the ETI "workarounds" the code compiles fine.  So my question is what is ETI, what does the ETI workaround provide, and how can I benefit from both the workaround and normal use of the code?

The code looks something like:

        std::find(boost::make_zip_iterator(boost::make_tuple(vector1.begin(), vector2.begin())), boost::make_zip_iterator(boost::make_tuple(vector1.end(), vector2.end())), ...

The beginning of the error looks something like this:

./../3rdParty\boost/iterator/detail/minimum_category.hpp(86) : error C2057: expected constant expression
        ../../3rdParty\boost/iterator/detail/minimum_category.hpp(112) : see reference to class template instantiation 'boost::detail::minimum_category<struct boost::random_access_traversal_tag,struct boost::random_access_traversal_tag>' being compi
led
        ../../3rdParty\boost/mpl/aux_/preprocessed/msvc60/apply.hpp(88) : see reference to class template instantiation 'boost::detail::minimum_category<struct boost::mpl::arg<1>,struct boost::mpl::arg<2> >::apply<struct boost::random_access_travers
al_tag,struct boost::random_access_traversal_tag>' being compiled
        ../../3rdParty\boost/mpl/aux_/preprocessed/msvc60/apply.hpp(101) : see reference to class template instantiation 'boost::mpl::aux::msvc_apply2<struct boost::detail::minimum_category<struct boost::mpl::arg<1>,struct boost::mpl::arg<2> > >::re
sult_<struct boost::random_access_traversal_tag,struct boost::random_access_traversal_tag>' being compiled
        ../../3rdParty\boost/iterator/zip_iterator.hpp(173) : see reference to class template instantiation 'boost::mpl::apply2<struct boost::detail::minimum_category<struct boost::mpl::arg<1>,struct boost::mpl::arg<2> >,struct boost::random_access_
traversal_tag,struct boost::random_access_traversal_tag>' being compiled

Thanks.