Re: [boost] [fusion] flatten/flatten_view Proposal

Subject: Re: [boost] [fusion] flatten/flatten_view Proposal
From: TONGARI J (tongari95_at_[hidden])
Date: 2013-10-23 23:35:52

Hi Eric,

2013/10/24 Eric Niebler <eniebler_at_[hidden]>

> On 10/23/2013 7:30 AM, TONGARI J wrote:
> > Hi there,
> >
> > I've created the ticket, doc&test included
> > https://svn.boost.org/trac/boost/ticket/9294
> >
> > 'flatten' is an algorithm which returns a view that allows you to go
> > through the leaf elems sequentially.
> >
> > For example:
> >
> >     flatten(make_vector(1, make_vector(2, 3))) == make_vector(1, 2, 3)
> >
> > This is developed when I use Fusion to work with SQL for simple data
> > mapping.
>
> You have duplicated a *huge* amount of work already in Fusion for
> supporting segmented sequences. If your Fusion sequence is logically a
> sequence of sequences, you just have to implement
> extension::is_segmented_impl and extension::segments_impl to make your
> type a valid Fusion sequence that has "flat" Fusion iterators.
> extension::segments_impl just has to return a Fusion sequence of Fusion
> sequences. See libs/fusion/test/sequence/tree.hpp for an example.
>
> Sorry this isn't documented. That's my fault. I'm doubly sorry that you
> went to the trouble of implementing this. Adding support to Fusion for
> segmented sequences is one of the reasons why I have no hair today. ;-)
>

I just tried to re-implement it by segments_impl, but seems to cause memory
violation.

Code is attached. Could you shed some light on this?
(note: flatten_view should be writable if the underlying sequence is
writable)

Thanks,