Re: [boost] [mpl]iter_fold_if Forward Backward rationale?

Subject: Re: [boost] [mpl]iter_fold_if Forward Backward rationale?
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2009-05-29 17:02:55

AMDG

David Abrahams wrote:
> on Tue May 19 2009, Larry Evans <cppljevans-AT-suddenlink.net> wrote:
>   
>>> Alas.  AFAICT, there are no tests or uses for the Backward Predicate
>>> in MPL.
>>>
>>>       
>> However, there may be a use in the future.
>>     
>
> That's really no excuse ;-)
>
> I think this is probably a case of premature generalization.
>   

Anything that can be done with the backward predicate can be done
by passing an appropriate boolean flag along with the result.  Unlike the
forward predicate, there are no big-O gains from having the algorithm
know about it.  The only case where it is significantly more convenient
to use the backward predicate is when doing both a forward and a reverse
operation.  For this case, what is really needed is the ability to give 
iter_fold_if
a lambda expression which will be used to package the result of the forward
operation for the backwards operation.  (This is all premature 
generalization
of course...)

In Christ,
Steven Watanabe