BiCollector

[Brian Goetz]

"bisecting" sounds like it sends half the elements to one collector and 
half to the other ...

"tee" might be a candidate, though it doesn't follow the `ing 
convention.  "teeing" sounds dumb.



On 6/15/2018 7:36 PM, Paul Sandoz wrote:
> Hi Tagir,
>
> This is looking good.
>
> My current favorite name for the factory method is “bisecting” since we are dividing the collector into two collectors, the results of which are then merged.
>   
> Suggested first paragraph of the factory method:
>
>    "Returns a collector that passes the input elements to two specified collectors and merges their results with the specified merge function.”
>
> Paul.
>   
>
>> On Jun 15, 2018, at 4:26 AM, Tagir Valeev <amaembo at gmail.com> wrote:
>>
>> Hello!
>>
>> I created a preliminary webrev of my own implementation (no testcases yet):
>> http://cr.openjdk.java.net/~tvaleev/patches/pairing/webrev/
>> If anybody wants to sponsor my implementation, I will happily log an issue and write tests.
>>
>> The name "pairing" was invented by me, but as I'm not a native English speaker I cannot judge whether it's optimal, so better ideas are welcome.
>> Also I decided to remove accumulator types from public type variables. They do not add anything to type signature, only clutter it
>> increasing the number of type parameters from 4 to 6. I think it was a mistake to expose the accumulator type parameter in other cascading collectors
>> like filtering(), collectingAndThen(), groupingBy(), etc. I'm not insisting though, if you feel that conformance to existing collectors is
>> more important than simplicity.
>>
>> With best regards,
>> Tagir Valeev.
>>
>> On Fri, Jun 15, 2018 at 5:05 AM Brian Goetz <brian.goetz at oracle.com> wrote:
>>
>>> Well, I don't see the need to pack the two results into a Map.Entry
>>> (or any similar) container as a drawback.
>>   From an "integrity of the JDK APIs" perspective, it is unquestionably a
>> drawback.  These items are not a Key and an associated Value in a Map;
>> it's merely pretending that Map.Entry really means "Pair".  There's a
>> reason we don't have a Pair class in the JDK (and no, let's not reopen
>> that now); using something else as a Pair proxy that is supposed to have
>> specific semantics is worse. (It's fine to do this in your own code, but
>> not in the JDK. Different standards for code that has different audiences.)
>>
>> Tagir's proposed sidestepping is nice, and it will also play nicely with
>> records, because then you can say:
>>
>>        record NameAndCount(String name, int count);
>>
>>        stream.collect(pairing(collectName, collectCount, NameAndCount::new));
>>
>> and get a more properly abstract result out.  And its more in the spirit
>> of existing Collectors.  If you want to use Map.Entry as an
>> _implementation detail_, that's fine.
>>
>> I can support this form.
>>
>>> I also don't see a larger abstraction like BiStream as a natural fit
>>> for a similar thing.
>> I think the BiStream connection is mostly tangential.  We tried hard to
>> support streams of (K,V) pairs when we did streams, as Paul can attest,
>> but it was a huge complexity-inflater and dropping this out paid an
>> enormous simplification payoff.
>>
>> With records, having streams of tuples will be simpler to represent, but
>> no more performant; it will take until we get to value types and
>> specialized generics to get the performance we want out of this.
>>
>>