Primitive streams and optional

[Brian Goetz]

Yes, "tolerate" might not be a good word, since sometimes it has a 
connotation of "I'll put up with it, but I don't like it" and sometimes 
a more positive "we're all brothers on this earth together."  In this 
case, I mean the more intolerant flavor of tolerance, and the spec 
should reflect that ;)

On 11/28/2012 10:59 AM, Remi Forax wrote:
> On 11/28/2012 04:27 PM, Doug Lea wrote:
>> On 11/26/12 15:43, Brian Goetz wrote:
>>
>>> 1.  Ban nulls.  This is equivalent to adding
>>>     .tee(e -> { if (e == null) throw new NPE(); }
>>> between all stages of a pipeline.
>>>
>>> 2.  Ignore nulls.  This is what Doug is proposing, and is equivalent
>>> to adding
>>>     .filter(e -> e != null)
>>> between all stages of a pipeline.
>>>
>>> 3.  Tolerate nulls.  This treat nulls as "just another value" and
>>> hopes that
>>> lambdas and downstream stages can deal.
>>>
>>
>> In case anyone was thinking that these have anything to do with
>> efficiency, remember that JVMs are required to null-check each
>> non-explicity-checked use of any reference anyway.
>> So these three choices have similar costs.
>>
>> (They do vary a little:  #3 will sometimes be the most expensive,
>> since the lack of a pre-null-check forces twistier code paths
>> to be generated later on first dereference of a field.)
>
> Yes, for #3, if someone call any stream pipelines without sending null,
> it's ok. If there is just one codepath that sends one null through one
> pipeline, the user will pay a high tax once because the VM may have to
> deoptimize a lot of pipeline codes (not just the code of one pipeline).
>
> Note that this may be not true in the future if the VM is able to
> specialize the code at the site of the call to the terminal op. In that
> case, send null will only affect one stream and not all of them.
>
> To summarize, the javadoc of Stream should be clear that it's not
> because streams tolerate null that users should send null through them.
> Also note that many implementations of collection/map exhibit the same
> issue if elements of collections or keys of map are once null.
>
>>
>> -Doug
>>
>
> Rémi
>