RFR 8071600: Add a flat-mapping collector

[Paul Sandoz]

On Feb 12, 2015, at 4:51 PM, Peter Levart <peter.levart at 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?

Thanks,
Paul.