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Subject: [boost] Stacking iterators vs. dataflow
From: Phil Endecott (spam_from_boost_dev_at_[hidden])
Date: 2008-09-03 08:36:23

I just noticed this in the "lifetime of ranges vs. iterators" thread
(which I've not really been following):

Arno Sch?dl wrote:
> rng | filtered( funcA )
> | filtered( funcB )
> | filtered( funcC )
> | filtered( funcD )
> | filtered( funcE )

I thought it worth pointing out the similarity, and also the
difference, between this and the proposed dataflow notation. Here,
operator| is being used like a shell pipe operator. In dataflow,
operator| has a quite different meaning: it's a vertical line,
distributing the output of "rng" to the inputs of the funcs in
parallel. Confusing, perhaps? Anyway you could presumably write
something like

   rng >>= funcA >>= funcB ....

and I would be interested to hear how the two implementations compare.
Is it true to say that stacked iterators implement a "data pull" style,
while dataflow implements "data push"?

I also note that Arno wants to use stacked iterators because this alternative:

  result = fn1( fn2( fn3( fn4( huge_document ) ) ) );

creates large intermediates and requires dynamic allocation. Again, a
framework that allowed buffering of "sensible size" chunks and
potentially distributed the work between threads could be a good solution.


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