what is the idomatic way to cancel a `flow` from within with an error? just throw an exception, or ...

# coroutines

[bj0]

what is the idomatic way to cancel a flow from within with an error? just throw an exception, or is there a function?

[kevin.cianfarini]

I do this in exactly one place in our codebase, but beware that it’s got edge cases.

flow {
  coroutineScope {
    try {
      ...
    } catch (e: SomeException) {
      // ... perform some side effect...
      cancel(message = "An error happened", cause = e)
    }
  }
}

[bj0]

if you use cancel will it consider a "normal" cancellation? so when you use .catch() on the flow later, it won't trigger will it?

[bj0]

oh, and you're cancelling the scope, which will end the flow normally, i want to cancel it with an error

[ephemient]

flow {
    throw exception // will end flow
}.catch {
    // will catch exception
}

[ephemient]

using coroutineScope inside flow makes it way too easy to do things that aren't supported and will throw errors at runtime (such as trying to emit from another coroutine), I wouldn't do that. if you want to end the flow gracefully, you can return@flow

[kevin.cianfarini]

In my case, I wanted to cancel the collector of the flow. Ending it gracefully means that certain operators, like Flow.first , would throw exceptions.