[OT] foreach(scheme) (Was: Differentiate const flavors using CASE?)

[kris]

Daniel Keep wrote:
> 
> kris wrote:
> 
>>janderson wrote:
>>
>>>Andrei Alexandrescu (See Website For Email) wrote:
>>>
>>>>
>>>>Yah :o). Speaking of foreach_reverse, probably it would be wise to
>>>>lobby Walter to deprecate it in favor of foreach(reverse) (item ;
>>>>collection) { ... }. The keyword(extra) syntax is definitely becoming
>>>>a D signature syntax.
>>>>
>>>>
>>>>Andrei
>>>
>>>
>>>//Using your other suggestion:
>>>foreach(reverse) (item ; collection) (item2 ; x->GetColection(b))
>>>(item3 ; collection3)
>>>{
>>>
>>>}
>>>
>>>Its starting to get hard and harder to read IMO.
>>>
>>>Although perhaps the reverse could be come sort of iterator mechanism.
>>>You could define what order items are visited.  I mean, reverse would
>>>not be a keyword at all and would exist in some library.  Although I'm
>>>not sure how it would be implemented, and it may defeat the purpose of
>>>foreach_reverse being optimal.
>>>
>>>Just a thought.
>>
>>shouldn't this perhaps be something like:
>>
>>foreach (item; collection) (item2; x->GetColection(b))(item3;
>>collection3.reverse)
>>{
>>
>>}
>>
>>
>>Now you can select a direction on the each container?
>>
>>Naturally, this would avoid performing a copy of the content, and the
>>basic approach is quite easy to handle via a struct containing an
>>opApply(). It would open the door to alternate iteration approaches
>>also, such as skipping entries, merging, or whatever.
>>
>>Tango does something vaguely like this for the text-iterators in
>>tango.text.Util
> 
> 
> What if collection3 is a 40 MB array?
> 
> The nice thing about foreach_reverse is that it doesn't require any
> transformations on the data.  

I didn't suggest transformation at all :) Merely a mean of satisfying 
opApply that happens to go backwards instead (or some other pattern).

Please, take a peek at tango.text.Util ... methods lines(), delimiters() 
and patterns() are examples of what I'm getting at. That particular 
approach can easily be adapted for any kind of container