src/main/java/io/reactivex/Flowable.java
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <R> Flowable<R> flatMapSingle(Function<? super T, ? extends SingleSource<? extends R>> mapper) {
        return flatMapSingle(mapper, false, Integer.MAX_VALUE);
    }
@CheckReturnValue
    @BackpressureSupport(BackpressureKind.UNBOUNDED_IN)
    @SchedulerSupport(SchedulerSupport.NONE)
    public final <R> Flowable<R> flatMapSingle(Function<? super T, ? extends SingleSource<? extends R>> mapper) {
        return flatMapSingle(mapper, false, Integer.MAX_VALUE);
    }
@ CheckReturnValue @ BackpressureSupport ( BackpressureKind . UNBOUNDED_IN ) @ SchedulerSupport ( SchedulerSupport . NONE ) public final < R > Flowable < R > flatMapSingle ( Function < ? super T , ? extends SingleSource < ? extends R > > mapper ) { return flatMapSingle ( mapper , false , Integer . MAX_VALUE ) ; }
Maps each element of the upstream Flowable into SingleSources, subscribes to all of them
and merges their onSuccess values, in no particular order, into a single Flowable sequence.
<dl>
<dt><b>Backpressure:</b></dt>
<dd>The operator consumes the upstream in an unbounded manner.</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code flatMapSingle} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
@param <R> the result value type
@param mapper the function that received each source value and transforms them into SingleSources.
@return the new Flowable instance
Maps each element of the upstream Flowable into SingleSources subscribes to all of them and merges their onSuccess values in no particular order into a single Flowable sequence . <dl > <dt > <b > Backpressure : < / b > < / dt > <dd > The operator consumes the upstream in an unbounded manner . < / dd > <dt > <b > Scheduler : < / b > < / dt > <dd > {