fix flatMapFirst

[hmhv]

No description provided.

[freak4pc]

Hey @hmhv - that looks great, thanks for the catch.

I was only wondering - flatMapFirst says:

If element is received while there is some projected observable sequence being merged it will simply be ignored.

Did you confirm maxPublishers: 1 has the same behavior where it drops streams during the processing of a previous one?

[hmhv]

What about this?

maxPublishers
The maximum number of publishers produced by this method.

https://developer.apple.com/documentation/combine/publisher/3204712-flatmap

[freak4pc]

That piece of docs isn't clear enough to be sure, so I tested this.
There is one key difference between RxSwift and Combine in this sense - and that's backpressure.

Here's the RxSwift example:

Note that every 3 seconds - the specific element emitted from the upstream is processing and others are "dropped" (like said in the docs)

Here's the Combine example:

Note that the upstream doesn't "drop items" at all - but never actually produces them since backpressure prevents the upstream from producing more elements. In this sense it's more like a concat since the flatMap is forced to complete before the upstream can product more elements.

I'm OK with listing it as a parallel even though ... in essence it's not too similar in behavior. What do you think ?

[freak4pc]

Messing with this a bit more - I wouldn't say this is like flatMapFirst.

I just realized Observable.merge(maxConcurrent: 1) is really the parallel of flatMap(maxPublishers: .max(1)).

[hmhv]

Thank you for your example. you are right.
flatMap(maxPublishers: .max(1)) is not ignored element

[freak4pc]

This is still a very good point though, so I've added it in 416ec07