Re: [Boost-users] [multi-index] Container of polymorphic pointers

Subject: Re: [Boost-users] [multi-index] Container of polymorphic pointers
From: Daniel Dilts (diltsman_at_[hidden])
Date: 2008-10-30 20:49:04

I appreciate the help.  This worked perfectly.

On Thu, Oct 30, 2008 at 1:10 AM, Joaquin M Lopez Munoz <joaquin_at_[hidden]>wrote:

> Daniel Dilts <diltsman <at> gmail.com> writes:
>
> > 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?
> >
> [...]
> >     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
>
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users