Re: [Boost-users] [MultiIndex] Key extraction from a base member

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2005-10-19 17:12:08

Hello Bruno, thanks for using Boost.MultiIndex!

----- Mensaje original -----
De: Bruno Martínez <br1_at_[hidden]>
Fecha: Miércoles, Octubre 19, 2005 10:46 pm
Asunto: [Boost-users] [MultiIndex] Key extraction from a base member

> Hi.
> 
> I have the following problem with MultiIndex.  For
> 
> struct Base {
> 	int id;
> };
> 
> struct Der : Base {
> };
> 
> I can't make a key extractor.
> 
[explanation on why it doesnt work snipped]
> Maybe the solution is to put some enable_ifs in member.
> 

Basically, something like that should be done, right.
Actually enable_if only works for highly compliant
compilers, so I'll have to resort to some uglier
mechanism, but it can be done. This is planned to
be solved (or added as a new feature, if you wish)
in Boost 1.34. The problem was first brought
to my attention in http://tinyurl.com/dnfzs.
In the meantime I'm afraid you are forced to write
your own key extractor (which is trivial, in any case.)

Best regards,

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo