iterators as first class objects

iterators as first class objects

[Lionel.DRAGHI]

| -----Message d'origine-----
| De: Robert I. Eachus 
...
| But the trick of having data structure packages return an 
| array view of 
| a collection, or actually an array of access values, is very, very 
| useful.

I also really like this idiom, but there are drawbacks:

1 - you get more job done:
First within the data structure component, you have to build the array. 
If the internal structure is not already an array, you will probably need an
actual iterator.
Then, within the user's code, there is the "for i in " loop.
With an iterator, there is only one loop.

2 - within the component, the whole array is build: with an iterator, you
may exit before the end.

This is why we use it only for small data structure. 

As this leads to crystal-clear user's code, and as it's a common need, I
think it's worth thinking about langage extension.
   
-- 
Lionel Draghi

Re: iterators as first class objects

[Robert I. Eachus]

Lionel.DRAGHI@fr.thalesgroup.com wrote:

> 2 - within the component, the whole array is build: with an iterator, you
> may exit before the end.
> 
> This is why we use it only for small data structure. 
> 
> As this leads to crystal-clear user's code, and as it's a common need, I
> think it's worth thinking about langage extension.

Which is why, as I said elsewhere I usually provide both the array view 
and a global next operation.  It is not an iterator because it removes 
the object from the structure before returning it.

If you want to think of this as an array view, and a queue view, fine, 
although the Next operation maps well to all data structures.  (If the 
user doesn't care about order (a bag) he still gets one item at a time 
with no repetition.


-- 
                                           Robert I. Eachus

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