Most clients of iterators won't care if they exhausted the iterator. The vast
majority of use cases looks like
for pat in iter {
// do stuff
}
// never touch iter again
For the few times where you might actually care, that's what the Fuse adaptor
is for, so you can say
let mut iter = iter.fuse();
// now the iterator conforms to behavior #1
-Kevin
On Aug 7, 2013, at 7:18 AM, Armin Ronacher <[email protected]> wrote:
> Hi,
>
> On 04/08/2013 02:18, Kevin Ballard wrote:
>> I believe that #3 is the right behavior to define. This gives the most
>> flexibility to individual iterators, and we can provide an iterator
>> adaptor that gives any iterator the behavior defined by #1 (see Fuse in
>> PR #8276 <https://github.com/mozilla/rust/pull/8276>).
> I think #3 is a terrible idea. It requires that every user of an iterator
> needs to keep track of if the iterator was exhausted and need to replace it
> with a dummy iterator that yields None forever or signal to other code that
> the iterator is exhausted. There is a lot of code that fetches a number of
> items from an iterator and then passes the iterator on to something else that
> does more with it.
>
> If I now need to check if the iterator was exhaused and then create a new and
> empty iterator to pass onwards to the other function it makes it a lot more
> complicated. Imagine this Python code:
>
> def dropwhile(predicate, iterable):
> iterable = iter(iterable)
> for x in iterable:
> if not predicate(x):
> yield x
> break
> for x in iterable:
> yield x
>
> If it's not guaranteed that an iterator returns None (StopIteration) after it
> was exhausted it needs to be rewritten to this:
>
> def dropwhile(predicate, iterable):
> iterable = iter(iterable)
> exhausted = True
> for x in iterable:
> if not predicate(x):
> yield x
> exhausted = False
> break
> if not exhausted:
> for x in iterable:
> yield x
>
> People will forget that they have to do this and cause bugs with composable
> iterator patterns. Just look through the Python itertools package for how
> many cases of partial iterator processing exist:
> http://docs.python.org/2/library/itertools.html
>
>
> Regards,
> Armin
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