src/main/java/io/reactivex/Single.java
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static <T> Single<T> merge(SingleSource<? extends SingleSource<? extends T>> source) {
        ObjectHelper.requireNonNull(source, "source is null");
        return RxJavaPlugins.onAssembly(new SingleFlatMap<SingleSource<? extends T>, T>(source, (Function)Functions.identity()));
    }
@CheckReturnValue
    @NonNull
    @SchedulerSupport(SchedulerSupport.NONE)
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static <T> Single<T> merge(SingleSource<? extends SingleSource<? extends T>> source) {
        ObjectHelper.requireNonNull(source, "source is null");
        return RxJavaPlugins.onAssembly(new SingleFlatMap<SingleSource<? extends T>, T>(source, (Function)Functions.identity()));
    }
@ CheckReturnValue @ NonNull @ SchedulerSupport ( SchedulerSupport . NONE ) @ SuppressWarnings ( { "unchecked" , "rawtypes" } ) public static < T > Single < T > merge ( SingleSource < ? extends SingleSource < ? extends T > > source ) { ObjectHelper . requireNonNull ( source , "source is null" ) ; return RxJavaPlugins . onAssembly ( new SingleFlatMap < SingleSource < ? extends T > , T > ( source , ( Function ) Functions . identity ( ) ) ) ; }
Flattens a {@code Single} that emits a {@code Single} into a single {@code Single} that emits the item
emitted by the nested {@code Single}, without any transformation.
<p>
<img width="640" height="412" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/Single.merge.oo.png" alt="">
<dl>
<dt><b>Scheduler:</b></dt>
<dd>{@code merge} does not operate by default on a particular {@link Scheduler}.</dd>
<dd>The resulting {@code Single} emits the outer source's or the inner {@code SingleSource}'s {@code Throwable} as is.
Unlike the other {@code merge()} operators, this operator won't and can't produce a {@code CompositeException} because there is
only one possibility for the outer or the inner {@code SingleSource} to emit an {@code onError} signal.
Therefore, there is no need for a {@code mergeDelayError(SingleSource<SingleSource<T>>)} operator.
</dd>
</dl>

@param <T> the value type of the sources and the output
@param source
a {@code Single} that emits a {@code Single}
@return a {@code Single} that emits the item that is the result of flattening the {@code Single} emitted
by {@code source}
@see <a href="http://reactivex.io/documentation/operators/merge.html">ReactiveX operators documentation: Merge</a>
Flattens a { @code Single } that emits a { @code Single } into a single { @code Single } that emits the item emitted by the nested { @code Single } without any transformation . <p > <img width = 640 height = 412 src = https : // raw . github . com / wiki / ReactiveX / RxJava / images / rx - operators / Single . merge . oo . png alt = > <dl > <dt > <b > Scheduler : < / b > < / dt > <dd > { @code merge } does not operate by default on a particular { @link Scheduler } . < / dd > <dd > The resulting { @code Single } emits the outer source s or the inner { @code SingleSource } s { @code Throwable } as is . Unlike the other { @code merge () } operators this operator won t and can t produce a { @code CompositeException } because there is only one possibility for the outer or the inner { @code SingleSource } to emit an { @code onError } signal . Therefore there is no need for a { @code mergeDelayError ( SingleSource<SingleSource<T >> ) } operator . < / dd > < / dl >