Method concatMap

src/main/java/io/reactivex/rxjava3/core/Flowable.java:7647–7653

Returns a new Flowable that emits items resulting from applying a function that you supply to each item emitted by the current Flowable, where that function returns a Publisher, and then emitting the items that result from concatenating those returned Publishers.

(@NonNull Function<? super T, @NonNull ? extends Publisher<? extends R>> mapper)

     * @see <a href="http://reactivex.io/documentation/operators/flatmap.html">ReactiveX operators documentation: FlatMap</a>
     */
    @CheckReturnValue
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    @NonNull
    public final <@NonNull R> Flowable<R> concatMap(@NonNull Function<? super T, @NonNull ? extends Publisher<? extends R>> mapper) {
        return concatMap(mapper, 2);
    }

    /**
     * Returns a new {@code Flowable} that emits items resulting from applying a function that you supply to each item