Yet another run at reduce (collect)

[Brian Goetz]

We have tried to follow the practice of treating all objects passed to 
stream methods as values.  So collectors can be reused.  You can 
singleton them as you suggest.

On 1/9/2013 5:50 PM, Aleksey Shipilev wrote:
> Thanks. Another question: it seems to me that collector passed into
> collect(...) can actually be reused, since I would expect the library
> will call makeResult() at least once to bootstrap the collector? Or, is
> the library reusing the one passed via the parameter? I.e. instead of:
>
>   stream().collect(new MyCollector()).getResult();
>
>   class MyCollector implements Collector<Long, MyCollector> {
>      public MyCollector makeResult() {
>          return new MyCollector();
>      }
>
>      public void accumulate(MyCollector result, Long value) {
>          result.result += value;
>      }
>
>      public MyCollector combine(MyCollector result, SumLongSink other) {
>          result.result += other.result;
>          return result;
>      }
>
>      public long getResult() {
>          return result;
>      }
>   }
>
> ...can I do this?
>
>   static final MyCollector MY_COLLECTOR = new MyCollector()
>   (...)
>   stream().collect(MY_COLLECTOR).getResult();
>
>
> -Aleksey.
>
> On 01/10/2013 01:13 AM, Brian Goetz wrote:
>> The simple rule is:
>>   - makeResult should return a new result container for every call
>>   - combine may return one of its arguments, or a new result
>>
>>
>>
>> On 1/9/2013 4:10 PM, Aleksey Shipilev wrote:
>>> On 01/09/2013 11:25 PM, Doug Lea wrote:
>>>> On 01/09/13 13:56, Brian Goetz wrote:
>>>>> I've pushed a rename to collect().  Check it out.
>>>>
>>>> Yay! Thanks!
>>>
>>> Ok, this is quite an intrusive change to adapt for my performance tests.
>>> Can you please add more Javadocs for Collector? In fact, I need more
>>> details on:
>>>    a) Should makeResult() return the new result on every call?
>>>    b) Can combine(result, other) return updated $result, or it should
>>> return distinct collectable?
>>>
>>> -Aleksey.
>>>
>