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

[Joe Bowbeer]

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
>>>
>>>
>>>
>>>
>>>
>>>
>>
>