Single.zip with empty Iterable should not throw NoSuchElementException

[valeriyo]

RxJava 2.2.17

The following method:

public static <T, R> Single<R> zip(final Iterable<? extends SingleSource<? extends T>> sources, Function<? super Object[], ? extends R> zipper)

throws NoSuchElementException if the Iterable sources is empty. This is very unfortunate, and it goes against functional programming principles.

The zipper function should be invoked with an empty array - and if zipper can handle empty Iterable - it will produce a value R. If zipper cannot handle an empty array - it's up to zipper to throw an exception. Basically, RxJava shouldn't put artificial constraints on the Iterable.

In my specific case, the zipper function is Kotlin's Iterable<T>.all(predicate: (T) -> Boolean) - which falls back to true if Iterable is empty - and that's what I want to receive - a Single of true.

Thanks.

#3789 was a wrong "fix" for the #3784 issue.

[akarnokd]

Works as intended. Use onErrorResumeNext to turn a NoSuchElementException into an item.

[valeriyo]

I disagree. Please fix it. It should work as expected without workarounds.

[akarnokd]

No. Use a workaround or create a custom zip operator with your expected behavior.

[valeriyo]

It's not my expected behavior. It's anyone's expected behavior that a library wouldn't throw exceptions for no good reason.