I have the following use case: I fire off a number of REST calls to a very slow REST service, and w...

# coroutines

[Paul N]

I have the following use case:

I fire off a number of REST calls to a very slow REST service, and want to return a filtered list of the results.

So currently I'm creating a channel, launching each REST call in a coroutine, and writing the result of each to a channel. I then iterate through the channel, do a manual filter via an if statement, and add any filtered result to a mutable list. This feels a bit imperative to me - is there a better way of doing this that doesn't for example, rely on a mutable list and manual filtering ? Should I be using Flow and filters instead ?

val output = mutableListOf<String>()
            for (something in channel) {
                if (some condition based on something) {
                    output.add(something)
                }

            }

[Dominaezzz]

I don't think you need a channel here.

[Dominaezzz]

Since you consume the entire thing at once.

[Dominaezzz]

Perhaps a List<Deferred<String>> instead of a channel.

[Dominaezzz]

Then you can do val output = TODO("Call REST and make deferred list").awaitAll().filter { some condition based on something }.

[Paul N]

Not sure if this will work - I have multiple REST calls all returning one item that I need to add to a collection once they have all finished - how would asynchronous jobs write to the deferred list ?

[Dominaezzz]

The jobs don't write to the list, the job scheduler does.

[Dominaezzz]

deferredList += async { } as supposed to async { deferredList += this }.

[ahulyk]

or use Flow<String> and filter{ } it. You also can combine multiple calls using flatMapMerge -> https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/flat-map-merge.html

[Paul N]

Thanks Domnic and Andrij - I'll try both.