I don't understand why we need IterableOnce ? Was: Proposal: JDK-8148917 Enhanced-For Statement Should Allow Streams

Peter Levart peter.levart at gmail.com
Fri Mar 15 08:24:53 UTC 2019

On 3/15/19 9:03 AM, forax at univ-mlv.fr wrote:
>>       * @since 13
>>       */
>>      interface Once {}
>> What do you think of that?
> It's not clear to me if an annotation, available at runtime, is not a better fit.
> Anyway, i'm not sure not sure introducing such interface/annotation worth its maintenance cost, as you said the use case is pretty narrow.

It is narrow, but in a situation like that, where you want to code an 
optimal generic algorithm and all you have access to is an Iterable, 
there's no other way (short of providing additional methods, which is 
ugly). Just think of this situation. You have to decide upfront if you 
need to buffer the elements obtained from 1st iteration or not, but 1st 
iteration always succeeds...

Annotations are not suitable for that as the check has to be quick and 
they don't play well with inheritance etc...


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