@BackpressureSupport(BackpressureKind.FULL)
    @CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <U> Flowable<U> flattenAsFlowable(final Function<? super T, ? extends Iterable<? extends U>> mapper) {
        ObjectHelper.requireNonNull(mapper, "mapper is null");
        return RxJavaPlugins.onAssembly(new MaybeFlatMapIterableFlowable<T, U>(this, mapper));
    }