Re: [Boost-users] [multiindex] [bind] Update members of the container between two iterators (was: Conversion loses qualifiers)

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2007-11-17 04:05:11

Hi Nebojsa,

----- Mensaje original -----
De: Nebojsa Simic <nelle_at_[hidden]>
Fecha: Sábado, Noviembre 17, 2007 0:05 am
Asunto: Re: [Boost-users] [multiindex] [bind] Update members of the 
container between two iterators (was: Conversion loses qualifiers)
Para: boost-users_at_[hidden]

> Nebojsa Simic wrote:
[...]
> > 
> > for_each( it
> >     , idxResponse.end()
> >     , boost::bind( &StatisticsByResponse::modify,
> > boost::ref(idxResponse), ::_1, fnAddStats )
> >   );
> > 
> > but it still does not compile (problem with boost::bind "wrong
> > number of arguments").
> > 
> > the call :
> > idxResponse.modify( it, fnAddStats );
> > works, so the problem is not the first bind, but the one in 
> > for_each.
[...]

You can't use for_each(it1,it2,someFunctor) to do what you want because
modify() needs an iterator, and for_each passes a value reference
to someFunctor rather than the iterator.
So, you've got to resort to a handmade loop like:

  for(StatisticsByResponse::iterator it=m_statistic.project<1>
(result.first),
                                     it_end=idxResponse.end();
      it!=it_end;++it){
    idxResponse.modify(it,boost::bind
(&Statistics::addStats,::_1,val,tick));
  }

A warning about modifying elements of a multi_index_container in
a loop: if your modification affects the key on which the index you're
traversing depends upon, then the loop is broken, because when
you call modify(...) the element will be rearranged in the index and
along with it the iterator "it". If this is your case, please read the
following post where mechanisms for range modifying are provided:

http://lists.boost.org/boost-users/2006/03/18048.php

(Note that post comes with some usable code attached). Hope this
helps, thanks for using Boost.MultiIndex, if something's still
not clear do not hesitate to come back.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo