RFR : JDK-8001642 : Add Optional<T>, OptionalDouble, OptionalInt, OptionalLong

[Joe Bowbeer]

Neat! Thanks.


On Fri, Mar 15, 2013 at 12:53 PM, Ali Lahijani <alahijani at gmail.com> wrote:

> I guess limit() can be used to achieve short circuiting:
>
> T findFirst(T ifNone) {
>   return limit(1).reduce(ifNone, (l, r) -> r);
>
> }
>
> On Fri, Mar 15, 2013 at 10:26 PM, Joe Bowbeer <joe.bowbeer at gmail.com>wrote:
>
>> It wasn't obvious to me until recently that it is the short-circuiting
>> behavior of the 'find' methods that is hardest to derive.
>>
>> Without short-circuiting, findFirst forms could be derived as follows, but
>> they will fail on infinite streams:
>>
>> T findFirst(T ifNone) {
>>   return reduce(ifNone, (l, r) -> (l != ifNone) ? l : r);
>> }
>>
>> T findFirst(Predicate<? super T> predicate, T ifNone) {
>>   return reduce(ifNone, (l, r) -> (l != ifNone || !predicate.test(r)) ? l
>> :
>> r);
>> }
>>
>> I'm not sure why, but I'm liking the idea of only adding
>> findAny(predicate,
>> ifNone).
>>
>> --Joe
>>
>>
>> On Fri, Mar 15, 2013 at 8:04 AM, Doug Lea <dl at cs.oswego.edu> wrote:
>>
>> > On 03/15/13 09:46, Brian Goetz wrote:
>> >
>> >> Wouldn't the minimal change NOT have a predicate, to match the existing
>> >> form of
>> >> findFirst?
>> >>
>> >>    Optional<T> findFirst()
>> >>    T findFirst(T orElse)
>> >>
>> >>
>> > Yes and no. The only way to get non-optional-bearing
>> > result for search would otherwise be s.filter(pred).findAny(),
>> > which entails buffering of stuff you will throw away.
>> >
>> > This is also the reason only adding why findAny(pred) (not findDirst)
>> > is defensible: the alternative is of most interest to the sort of
>> > person who want to avoid that Optional too.
>> >
>> > -Doug
>> >
>> >
>> >
>> >
>> >
>> >> On 3/15/2013 7:31 AM, Doug Lea wrote:
>> >>
>> >>> On 03/15/13 06:26, Joe Bowbeer wrote:
>> >>>
>> >>>> Doug,
>> >>>>
>> >>>> I think your point that Optional and non-Optional forms of reduce are
>> >>>> already
>> >>>> provided is significant.
>> >>>>
>> >>>> I noticed that your proposed versions of findFirst and findAny have a
>> >>>> Predicate
>> >>>> argument, but the Optional forms do not:
>> >>>>
>> >>>> T findFirst(Predicate<? super T> predicate, T ifNone);
>> >>>>
>> >>>> Why is this?
>> >>>>
>> >>>
>> >>>
>> >>> It's in the spirit of proposing a minimal change. The predicate
>> >>> form suffices for all Optional-avoiding search stuff. To reduce
>> >>> impact by another 50%, it would suffice to ONLY include the "any"
>> form.
>> >>>    T findAny(Predicate<? super T> predicate, T ifNone);
>> >>>
>> >>> -Doug
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>
>> >
>>
>
>