Delay with subscription and item delaying observables.

[akarnokd]

Listed in #653

Note: onError and onCompleted events of the source are immediately propagated and will prevent emitting any pending values.

[cloudbees-pull-request-builder]

RxJava-pull-requests #648 SUCCESS
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[zsxwing]

Do the following codes do the same thing?

    public <U> Observable<T> delay(
            final Func1<? super T, ? extends Observable<U>> itemDelay) {
        return flatMap(new Func1<T, Observable<T>>() {
            @Override
            public Observable<T> call(final T t1) {
                return itemDelay.call(t1).take(1).map(new Func1<U, T>() {
                    @Override
                    public T call(U ignored) {
                        return t1;
                    }
                });
            }
        });
    }

[akarnokd]

I checked Rx.NET and both onNext and onCompleted of the itemDelay's Observable trigger the value emission so this and mine is incorrect.

[cloudbees-pull-request-builder]

RxJava-pull-requests #660 SUCCESS
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