src/main/java/io/reactivex/Single.java
@CheckReturnValue
    @NonNull
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static <T> Flowable<T> mergeDelayError(Publisher<? extends SingleSource<? extends T>> sources) {
        ObjectHelper.requireNonNull(sources, "sources is null");
        return RxJavaPlugins.onAssembly(new FlowableFlatMapPublisher(sources, SingleInternalHelper.toFlowable(), true, Integer.MAX_VALUE, Flowable.bufferSize()));
    }
@CheckReturnValue
    @NonNull
    @BackpressureSupport(BackpressureKind.FULL)
    @SchedulerSupport(SchedulerSupport.NONE)
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public static <T> Flowable<T> mergeDelayError(Publisher<? extends SingleSource<? extends T>> sources) {
        ObjectHelper.requireNonNull(sources, "sources is null");
        return RxJavaPlugins.onAssembly(new FlowableFlatMapPublisher(sources, SingleInternalHelper.toFlowable(), true, Integer.MAX_VALUE, Flowable.bufferSize()));
    }
Merges a Flowable sequence of SingleSource instances into a single Flowable sequence,
running all SingleSources at once and delaying any error(s) until all sources succeed or fail.
<dl>
<dt><b>Backpressure:</b></dt>
<dd>The returned {@code Flowable} honors the backpressure of the downstream consumer.</dd>
<dt><b>Scheduler:</b></dt>
<dd>{@code mergeDelayError} does not operate by default on a particular {@link Scheduler}.</dd>
</dl>
<p>History: 2.1.9 - experimental
@param <T> the common and resulting value type
@param sources the Flowable sequence of SingleSource sources
@return the new Flowable instance
@see #merge(Publisher)
@since 2.2