Re: RFR 8071600: Add a flat-mapping collector

[Peter Levart]

On 02/12/2015 05:07 PM, Paul Sandoz wrote:

On Feb 12, 2015, at 4:51 PM, Peter Levart <peter.lev...@gmail.com> wrote:

Hi Paul,

Would the following "optimization" make any sense?

     public static <T, U, A, R>
     Collector<T, ?, R> flatMapping(Function<? super T, ? extends Stream<? extends 
U>> mapper,
                                    Collector<? super U, A, R> downstream) {
         BiConsumer<A, ? super U> downstreamAccumulator = 
downstream.accumulator();
         return new CollectorImpl<>(downstream.supplier(),
             (r, t) -> {
                 try (Stream<? extends U> result = mapper.apply(t)) {
                     if (result != null) {
                         ((result.isParallel() &&
                             
!downstream.characteristics().contains(Collector.Characteristics.CONCURRENT))
                             ? result.sequential() : result).forEach(u -> 
downstreamAccumulator.accept(r, u));
                     }
                 }
             },
             downstream.combiner(), downstream.finisher(),
             downstream.characteristics());
     }

Ah, interesting.

Possibly... i need to think thought the implications on stream and collectors 
(groupingByConcurrent does the right thing for a non-concurrent downstream 
collector and synchronizes on the accumulation).

Do you mind if i treat that as a separate issue?

I don't mind, of course. It was just a thought.

Regards, Peter

Thanks,
Paul.