Re: [Boost-users] [multi_index] iterating over keys and "extracting" key extractors

Subject: Re: [Boost-users] [multi_index] iterating over keys and "extracting" key extractors
From: Nick Stokes (randomaccessiterator_at_[hidden])
Date: 2015-03-19 09:09:38

Thanks Joaquín

On Wed, Mar 18, 2015 at 3:45 PM, Joaquin M Lopez Munoz <joaquin_at_[hidden]>
wrote:

> Nick Stokes <randomaccessiterator <at> gmail.com> writes:
>
> >
> > Q1:  Is there a builtin in way in MI to iterate over keys rather
> > than elements? I.e. the iterator's value type will be that of the
> > key, not the element.
>
> No, there's none. Some iterator adaption is needed as you mention
> below.
>
> > Q2:  Is there a way to obtain the type of key extractors given a
> > multi index container?  (it is related to Q1, as this sort of a
> > thing could be passed to boost::transform iterator to obtain an
> > alternative answer for Q1)
>
>   auto beg=boost::make_transform_iterator(
>              foos.get<1>().begin(),foos.get<1>().key_extractor()),
>        end=boost::make_transform_iterator(
>              foos.get<1>().end(),foos.get<1>().key_extractor());
>
>   std::copy(
>     beg,end,std::ostream_iterator<std::string>(std::cout," "));
>
> Joaquín M López Muñoz
> Telefónica
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