Hi guys, i’m writing a `startWith` extension on `R...

# coroutines

[mboudraa]

Hi guys, i’m writing a startWith extension on ReceiveChannel and i was wondering which is the best way to do that.
I have currently 2 implementations:

suspend fun <A> ReceiveChannel<A>.startWith(element: A): ReceiveChannel<A> {
    val channel = Channel<A>()
    channel.offer(element)
    consumeEach { channel.send(it) }
    return channel
}

suspend fun <A> ReceiveChannel<A>.startWith(element: A, coroutineScope: CoroutineScope): ReceiveChannel<A> {
    return coroutineScope.produce {
        offer(element)
        [e-mail] { [e-mail](it) }
    }
}

I’m not sure what’s the difference is between the 2 and which is the best approach

[streetsofboston]

I would prefer the first one, even if it is just for the simple reason it doesn’t need an additional CoroutineScope parameter.

Sidenote: You call offer, but that could fail. Wouldn’t that mean the returning channel won’t start with element?

[mboudraa]

it fails only if the channel don’t have the room to send the offered element. since it’s the first one. should never happen

[streetsofboston]

Yes, you’re right. The channel is brand ‘new’ 🙂

[marstran]

I think you should make sure that the output channel has the same capacity as the input channel.

[mboudraa]

looks like the 1st implementation doesnt work anyway

[mboudraa]

So the solution is either the second using send or using GlobalScope to avoid forwarding the CoroutineScope everytime

[dave08]

1st probably doesn't work because it's a rendez-vous channel, if it has at least capacity 1, it should be fine.