Hey, I'm wondering if there is an operator on `Flo...

# coroutines

[svenjacobs]

Hey, I'm wondering if there is an operator on Flow that achieves the following: If the Flow has not produced at least one value in a given timeframe (x miliseconds), produce a default value followed by any values the Flow might produce afterwards. In contrast to a solution with debounce however, if the Flow has produced a value before the timeframe, the default value will just be ignored and the value will be emitted immediatly.

[svenjacobs]

Something like a delayedDefault 😉

[svenjacobs]

I built something myself but I'm not sure if this is the best solution 😁

fun <T> Flow<T>.delayedDefault(
    defaultAfter: Long,
    defaultValue: () -> T
): Flow<T> =
    channelFlow {
        val job = launch {
            delay(defaultAfter)
            offer(defaultValue())
        }

        collect {
            job.cancel()
            offer(it)
        }
    }

[elizarov]

Looks good to me. However, it would be safer to use send(defaultValue()) just in case somebody does delayedDefault(…).buffer(0).

[svenjacobs]

Okay, thanks for the feedback from the expert 👍🏼 😉

[elizarov]

You should also add one more job.cancel() after collect, so that it does not wait in the corner case of empty flow (flowOf().delayedDefault(…))

[svenjacobs]

Oh, right!

[elizarov]

Unless you want delay+default in this case, too

[svenjacobs]

Should I also use send() inside collect?

[elizarov]

Yes, that, too

[svenjacobs]

Cancelling an already cancelled Job will do nothing, right? No exception will be thrown?

[elizarov]

Yes. It is perfectly fine and it is quite fast, too.