[boost] Re: Boost Algorithms Library

From: Joel de Guzman (joel_at_[hidden])
Date: 2005-03-21 21:45:36

David Abrahams wrote:

> Whether results should be lazy (as in Fusion) or greedy, as in
> standard algorithms, or whether both variants should be provided
> somehow, are interesting questions.  The answers change the usage
> pattern, i.e.:
> 
>   copy(transform(s1,op), output)
> 
> or 
>   output = transform(s1,op)  // if output supports it
> 
> vs.
> 
>   transform(s1,op,output)

WRT Fusion, I am re-considering its laziness. MPL algorithms are
sequence preserving. Fusion is not, due to laziness. i.e:

     transform(tuple, op)

does not return a sequence like tuple. instead, it returns a
view (transform_view).

However, I realize now, that in most use cases, I noticed that I
had to eagerly generate the result into a tuple almost as immediately
after each transform step.

After leaving this for a while in my thought queue, and after
implementing phoenix2's lazy STL algorithms, I realized that
the lazy Fusion algorithms could as well be implemented as
phoenix2's lazy fusion algorithms. If I implemented Fusion
algorithms as non-lazy and sequence preserving like MPL, I could
easily write lazy fusion algorithms through phoenix.

I am still unsure about which is the best way to go. I just
thought I'd share my recent thoughts on the issue.

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