Re: [boost] lifetime of ranges vs. iterators

Subject: Re: [boost] lifetime of ranges vs. iterators
From: David Abrahams (dave_at_[hidden])
Date: 2008-09-03 09:11:47

on Tue Sep 02 2008, "Giovanni Piero Deretta" <gpderetta-AT-gmail.com> wrote:

>> Great, but what are you doing with these stacks?  Normally, the answer
>> would be something like "I'm applying the X algorithm to a range of
>> elements that represent Y but have been adapted to look like Z"
>>
>
> Usually is a matter of converting a text document to a point in a
> feature vector space as a preprocessing stage:

e.g., for the purposes of search?  Just trying to get a feel for what
you're describing.

> Most pipelines start with tokenization, normalization, filtering and
> hashing, with a 'take' operation at the end.

By 'take' you mean a destructive read?

> The resulting range is usually sorted (which implies breaking the
> laziness), 

Yep.

> unique-ed and augmented with score information (another map).
>
> I very often need to compute set union and intersection of pair of
> these ranges.
> [I do not have yet a lazy adaptor for this (actually I do, but is kind
> of experimental)].

Okay.

> Most of the uses of lazy ranges are in relatively non performance
> critical part of the application, so I do not aim for absolute zero
> abstraction overhead.

Okay, so... is it worth breaking up the iterator abstraction for this
purpose?

> A nice thing of lazy ranges is that are useful to control peak memory
> usage of the application (in fact if you are careful, you can do very
> little dynamic memory allocation)

Yes.

> I'm interested in using dynamic iterators in the near future for code
> decoupling 

You mean, like, any_iterator?

> and It would be a pity if these ranges couldn't fit in a small object
> optimization buffer.

Do you know how big that target ("small object optimization buffer") is?

-- 
Dave Abrahams
BoostPro Computing
http://www.boostpro.com