On Tue, Jul 14, 2009 at 5:11 PM, JOAQUIN M. LOPEZ MUÑOZ<joaquin@tid.es> wrote:

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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<typename MultiIndexContainer,typename Tag> struct has_index:  boost::mpl::contains<    boost::mpl::transform_view<      typename MultiIndexContainer::index_type_list,      boost::mpl::contains<tag_list<boost::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<T0,T1,T2>' 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<typename BMI, typename TAG> struct has_index { typedef typename BMI::index_type_list index_type_list; typedef typename mpl::end<index_type_list>::type index_type_list_end; typedef typename has_tag<TAG>::template apply<index_type_list>::type iter; BOOST_STATIC_CONSTANT(bool, value =!(is_same<iter, index_type_list_end>::value)); };

On Tue, Jul 14, 2009 at 5:49 PM, JOAQUIN M. LOPEZ MUÑOZ<joaquin@tid.es> wrote:

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    using namespace boost;     using boost::multi_index::detail::has_tag;

    template<typename BMI, typename TAG>     struct has_index {         typedef typename BMI::index_type_list index_type_list;         typedef typename mpl::end<index_type_list>::type index_type_list_end;         typedef typename has_tag<TAG>::template apply<index_type_list>::type iter;

has_tag applies to each index individually, not the entire index_type_list.

I see it now. Thanks for pointing it out. One last question tonight :) Similarly to how I can now statically enable/disable code based on which index is implemented by a BMI, can one also change that code based on whether the index is unique vs non-unique? Or ordered vs hashed? For example, using D's static if, could I do static if (index.is_unique) { // using index.find } else { // using index.equal_range } Thanks, --DD

On Fri, Jul 17, 2009 at 9:07 AM, Joaquin M Lopez Munoz<joaquin@tid.es> wrote:

Dominique Devienne <ddevienne <at> gmail.com> writes:

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On Tue, Jul 14, 2009 at 5:49 PM, JOAQUIN M. LOPEZ MUÑOZ<joaquin <at> tid.es>

One last question tonight :)

Sorry it's been a little later than that. I've been offline for the last couple of days.

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Similarly to how I can now statically enable/disable code based on which index is implemented by a BMI, can one also change that code based on whether the index is unique vs non-unique? Or ordered vs hashed? [...]

Use index_specifier_type_list instead of index_type_list (differences explained at http://tinyurl.com/nwe27r ) and resort to something like this:

 template<typename IndexSpecifier>  struct is_unique_index:boost::mpl::false_{};

 template<typename TagList,typename KeyFromValue,typename Compare>  struct is_unique_index<    boost::multi_index::ordered_unique<TagList,KeyFromValue,Compare>  >:boost::mpl::true_{};

 template<typename TagList,typename KeyFromValue,typename Hash,typename Pred>  struct is_unique_index<    boost::multi_index::hashed_unique<TagList,KeyFromValue,Hash,Pred>  >:boost::mpl::true_{};

and similarly for ordered vs hashed.

Thanks. Partial specialization I understand at least :) Although that's the first time I see the specialization having more template arguments than the base template, and that threw me off initially, but I see there's still a single template argument in is_unique_index, which happens to be a template itself. Thanks a bunch. --DD