Daniel Dilts
I'm am using boost::multi_index to hold a set of polymorphic entities. Due to efficiency concerns, I have to be able sort the container based on actual type. I was planning on sorting based on the return result of typeid. When I try this I get errors in <functional>. I am using VC++ 2005 Standard Edition SP1. What am I doing wrong, or, what is a better way of accomplishing what I am trying to do?
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struct extractType { typedef const type_info& result_type;
Here is the first problem: you've got to define typedef type_info result_type and let operator() return value be const result_type& (instead of the current return_type). Past the first hurdle you'll find that type_info is not comparable with <, so you'll also need to provide a custom comparer for this type based on type_info::before. The following summarizes all the changes needed (note: do not forget to include <typeinfo>; also, you're using type_info instead of std::type_info, which seems to work in VS but is not standard as far as I know): namespace Entities { struct type{}; struct extractType { typedef std::type_info result_type; const result_type& operator()(const Entity * r)const { return typeid(*r); } }; struct lessType { bool operator()(const std::type_info& x, const std::type_info& y)const { return x.before(y); } }; typedef boost::multi_index::multi_index_container< Entity *, boost::multi_index::indexed_by< boost::multi_index::ordered_non_unique< boost::multi_index::tag<type>, extractType, lessType > > > EntityContainer; }; Hope this helps. Thank you for using Boost.MultiIndex. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo