Re: [Boost-users] [Multi-Index] has_index<BMI,TAG> meta-function

On Tue, Jul 14, 2009 at 5:11 PM, JOAQUIN M. LOPEZ MUÑOZ wrote:

...

I'd like to use enable_if/disable_if with a meta-function that determines whether a given multi-index container has a given tagged index. You can use this:

template<typename Index> struct tag_list {  typedef typename Index::tag_list type; };

template struct has_index:  boost::mpl::contains<    boost::mpl::transform_view<      typename MultiIndexContainer::index_type_list,      boost::mpl::containsboost::mpl::_,Tag>    >,    boost::mpl::true_  > {};

Thanks. This appears to be working for me (i.e. I'm getting to errors past this code, which I'll need to clear before I can fully test it). My own attempt below fails on tag_list precisely, and I don't understand why. Your post came just in time :) Although if someone can point where mine went wrong, I'm still interested. Once again, thank you Joaquín! --DD error C2039: 'tag_list' : is not a member of 'boost::mpl::vector3' boost\multi_index\detail\has_tag.hpp 31 error C2146: syntax error : missing ',' before identifier 'tag_list' boost\multi_index\detail\has_tag.hpp 31 error C2065: 'tag_list' : undeclared identifier boost\multi_index\detail\has_tag.hpp 31 error C2955: 'boost::mpl::contains' : use of class template requires template argument list boost\multi_index\detail\has_tag.hpp 32 using namespace boost; using boost::multi_index::detail::has_tag; template struct has_index { typedef typename BMI::index_type_list index_type_list; typedef typename mpl::end::type index_type_list_end; typedef typename has_tag<TAG>::template apply::type iter; BOOST_STATIC_CONSTANT(bool, value =!(is_same::value)); };