What's the most idiomatic way to listen to multiple channels of different types and run a method with all the latest values each time? I mean, let's say I have

channelA: Channel<A>

and

channelB: Channel<B>

, I want to call a method like

update(a: A, b: B)

each time I get a value from any channel, that is, if I receive from

channelA

, I want it to be called with the new

A

value, and the same

B

value as previously received. Each time I have a use case for it, I feel like I'm writing disposable/throwaway code that is a bit error-prone and quite boilerplate-y. If you have any clue about a solution to do it right once for all, in a kind of generic way, please tell! Bonus points if your solution can also work with other callbacks and not just

Channel

maybe something like

merge

operator would help? Just merge multiple channels to one

Yes, probably, but I'm not aware of anything like this existing for

Channel

(I've searched through autocompletion, and I only found

zip

which does not do what I want as it needs a new value from each channel)

ZipOnFirst?

I think what I'm looking for is kind of a conflated zip, and preferably without allocation of intermediate objects like

Pair

,

Triple

or other grouping objects, if this is possible

Yeah, merge is not available as I know, but you can easily write own implementation, something like:

fun <T> merge(vararg channels: ReceiveChannel<T>) = produce {
    for (c in channels) {
        launch(coroutineContext) {
            for (v in c) {
                send(v)
            }
        }
    }
}

(just a draft, not tested, probably can be rewritten with select instead)

I don't know how to use select 😅

Yeah correct, or just use consumeEach

consumesAll

seems less efficient that a simple

forEach

in this case

You can use a sealed class where each channel returns a different sub-type

I found a solution to my use case, that can conflate multiple channels and callbacks together into one channel. Here's the source code: https://gist.github.com/LouisCAD/d9d1adbd3b4fd36d9dc121658fefd16f If you are interested but don't understand how it works, feel free to ping me, I'll show you a snippet or add an example to the gist that uses the class.

i probably would have used select...

@bj0 How? Until now I've had a hard time using it

i mean it just returns the first item available from either channel

That's not what my code is designed for. It transforms conflated values to a single one when

conflateAll

is called (on each update from any callback/channel)

ah well

select

would take care of the 'get a value from any channel' part

are you looking for this? https://github.com/ReactiveX/RxJava/wiki/Combining-Observables#combinelatest

@Daniel Tam Yes, this is exactly what I'm looking for, but I'm not using RxJava. I have a preference for the solution I implemented because it can work with any callbacks, not just channels