Combine Publisher needs back pressure management

[gahntpo]

Issue created in response to #27

According to Apple Combine Subscriptions have to fulfill the contract between publishers and subscribers with backpressure management. This is discussed in the WWDC presentation https://developer.apple.com/videos/play/wwdc2019/722/
The UIControl Event publisher is missing handling of the subscriber's demand. This is so far simply ignored.

I would like to add the demand management

[freak4pc]

I'm not opposed to simply pulling DemandBuffer from CombineExt into the project to deal with back pressure but I have to say that limiting demand for UI events is a highly unlikely use case. Do you have such a practical use case or are you more interested in the technical completeness ?

Thanks

[gahntpo]

If I have a subscriber with a request that is not unlimited, it is simply ignored. The use case would be starting fetches
flatmap(maxPublisher: .max(2) ) { url in URLSession.default.dataTaskPublisher(for url:) }
the maxPublisher allows me to decide how many network requests I want to do concurrently. once the flatmap is finished with one network request, it will send a new demand to its publisher. and receive the new value. This helps me to do batch requests with flatmap. I can also set max(1) to do my network requests in serial. But for this to work properly the upstream publisher needs to fulfill the demand handling.

[freak4pc]

Thanks, I think you misunderstood what I'm asking.
I'm asking what is the use case for back pressuring UI events (like ControlEvent/ControlTarget publishers) ?

flatMap itself still respects back pressure so using the format you mentioned here shouldn't be affected by CombineCocoa to the best of my understanding.

[freak4pc]

Closing for now. If you have additional details / context on this please let me know and I can reopen. Thank you! :)