On Thu, Oct 30, 2008 at 1:10 AM, Joaquin M Lopez Munoz <joaquin@tid.es> 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

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