Possible addition of a default 'getOne' method on Iterable? (original) (raw)

Paul Sandoz paul.sandoz at oracle.com
Wed Jan 31 22:02:13 UTC 2018

See also Stream.findFirst and findAny. Stream is the place we have and I think we should primarily focus effort on rather than Iterable for such features.

I believe a related feature some have requested is the ability to obtain an only, or at most, one element. On Stream this might manifest as:

T findOne(); Optional findAtMostOne(); // See Guava’s MoreCollectors/onlyElement,toOptional [1]

which might differ in terms of exceptions thrown compared to other terminal operations.

Paul.

[1] https://google.github.io/guava/releases/21.0/api/docs/com/google/common/collect/MoreCollectors.html#onlyElement-- <https://google.github.io/guava/releases/21.0/api/docs/com/google/common/collect/MoreCollectors.html#onlyElement-->

On Jan 30, 2018, at 10:09 PM, Dave Brosius <dbrosius at mebigfatguy.com> wrote:

Basically, but it's annoying and ugly to write most likely sub-optimal has problems with things like synchronized collections

On 01/31/2018 12:28 AM, Zheka Kozlov wrote: Isn't iterable.getOne() the same as iterable.iterator().next()?

2018-01-31 12:15 GMT+07:00 Dave Brosius <dbrosius at mebigfatguy.com <mailto:dbrosius at mebigfatguy.com>>: Greetings,

sorry if this has been asked before, but has there been any consideration for adding a default T getOne() { Iterator it = iterator(); if (!it.hasNext()) { throw new NoSuchElementException(); } return it.next(); } on the Iterable interface? It is often the case you have a collection of some sort (un indexed, in this case), where you know there is only one value in the collection, or you know for some attribute of all the objects in the Iterable, all objects can be thought of as the same, and so you just want to get any of the elements. Having to craft this iterator code is annoying, and it would be much nicer to be able to do String s = mySet.getOne(); In addition to this, it is likely that most collections could implement getOne() more optimally than using the standard iterator approach. Of course i am not stuck on the choice of the name 'getOne' anything would do. examplar() ? As we know, naming is always the hardest part. thoughts? dave

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