Re: segmented fusion - a-ha!

Eric Niebler wrote:
> I just had an a-ha! moment. Segmentation in Fusion is *so* much simpler 
> than I was making it. Fusion doesn't need segmented iterators, it needs 
> segmented sequences! Fusion's algorithms don't take iterators like the 
> std algorithms do -- they take sequences. I was trying to shoe-horn Matt 
> Austern's formulation into Fusion, but that's the wrong approach.
>
> Consider the joint_view. It should advertise itself as a segmented view. 
> Then, the only thing it needs to provide is a way to step through the 
> internal segments -- which are Fusion sequences that may or may not be 
> segmented. What you get, essentially, is:

Yeah! This is "make it as simple as possible" thing that I was
looking for. Essentially, segmented sequences are sequences with
child sequences (segments). I see:

    traits::is_segmented<Seq>::type // --> mpl::true_/false_

Then for segmented sequences:

    segments(seq) // --> a sequence of sequences
    result_of::segments<Seq>::type // --> a sequence of sequences type

Now, a joint_view can hold and return a vector2<Sequence1, Sequence2>&
when its intrinsic "segments" is called (via tag-dispatch).

Now, if for_each was an object (ala Fusion1), then segmented for_each
will simply be:

    for_each(segments(seq), for_each);

(Strike 1 for object algorithms, Dave?)

Effectively, each segment is unrolled for us by the mechanism
that already exists in fusion!

I think this is cool! This is more elegant than I expected it to be.
I like it! No, I love it!

Regards,
--
Joel de Guzman
http://www.boost-consulting.com
http://spirit.sf.net



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