Howdy, could someone suggest a better way to wrap a `callbackFlow` in `Either` ? I came up with that...

# arrow

[Alex Yordanov]

Howdy, could someone suggest a better way to wrap a callbackFlow in Either ? I came up with that but it looks kind of funky:

val flow = callbackFlow<Unit> {
    delay(2000)
    cancel(CancellationException("Boom"))
}

Either.catch {
    flow
        .catch { throw RuntimeException(it.message) }
        .collect()
}.mapLeft { it.message?.let { msg -> FlowError.Canceled(msg) } }

[simon.vergauwen]

Hey Alex,

What exactly is your use-case? Normally Flow would result in many results, but Either only has a single result. Are you just interested in capturing the cancelled event, or success? I think here your final result is Either<FlowError.Canceled?, Unit>.

[Sam]

Reminds me a little of a question I asked on StackOverflow once

[Alex Yordanov]

Hey Simon, in my exact use case I have just a single value that I’m expecting from the flow (along with the possible cancellations/failures). The code snippet that I used was illustrative

[simon.vergauwen]

If you're only expecting a single value, why not use suspend fun with suspendCoroutineCancellable? Then you could do something like:

either<Error, Res> {
  val res: Res = guaranteeCase({ action() }) { exitCase ->
    when(exitCase) {
     ExitCase.Completed -> Unit
     ExitCase.Failure -> Unit
     ExitCase.Cancelled -> shift(FlowError.Canceled(it.message ?: ""))
    }
  }
}

[simon.vergauwen]

Or

either<Error, Res> {
  val res: Res = onCancel({ action() }) {
    shift(..)
  }
}

[Alex Yordanov]

Thank you very much!