I guess this is a workaround although it is kinda jank

Question

gildor · Answer

Yes suspending delegates are not available now at least because properties which do not support suspend modifier at least for now Do you have particular use case for this I m not really sure what you doing in your code and why do you need delegate there instead of simple assignment just `val a = aAsync await ` without any delegation

Andrew Gazelka · Answer

alright so I am taking two `Flow`s of data and I am passing them into a HOF which will do calculations over time and want the latest value of the `Flow` which will update over time the reason for suspending at first is to wait until the first value from `Flow`s are returned

gildor · Answer

I mean that usually if you want to do some async operation only once as lazy works you can just create async save it to some field and than clients just call await on the same instance each of them will receive the same result await will be run only once

gildor · Answer

Hmm hard to say without example of code not really sure that you can use Flow for such case but maybe you could give a bit more context

gildor · Answer

What is HOF

gildor · Answer

Just if you have 2 Flows and want somehow combine their data shouldn t you use some zip or combineLatest operator depending on case

Andrew Gazelka · Answer

HOF is a higher order function

Andrew Gazelka · Answer

also I am not zipping data

Andrew Gazelka · Answer

I am essentially turning the two flows into sources which can be polled from another long running suspending function

gildor · Answer

Polled Hmm but it s cold stream there is no polling of data it s push based source

gildor · Answer

Looks that you need some Conflated broadcast channel to poll data

gildor · Answer

But hard to day without some sample

Andrew Gazelka · Answer

I think that makes sense I am using a websocket to get prices of currencies

Andrew Gazelka · Answer

so initially it is a cold stream new websocket created with initial function but it should then be converted to a hot stream when referenced by functions which require polling

Andrew Gazelka · Answer

< gildor> a ConflatedBroadcastChannel looks nice but I need a good way to suspend until the first value is received any ideas

gildor · Answer

Yes use receive

Andrew Gazelka · Answer

< gildor> but `receive ` removes the last element what if someone called `receive ` twice for one value

gildor · Answer

But you cannot remove element from ConflatedBroadcastChannel

gildor · Answer

ConflatedBroadcastChannel receive you will just get current value

Andrew Gazelka · Answer

there is no `receive ` method in `ConflatedBroadcastChannel`

Andrew Gazelka · Answer

I mean I guess I could use Mutexes but aren t those generally seen as bad

gildor · Answer

ConflatedBroadcastChannel openSubscription receive

gildor · Answer

or even better just ConflatedBroadcastChannel value

Andrew Gazelka · Answer

but I need to suspend until the first value is received

Andrew Gazelka · Answer

so `ConflatedBroadcastChannel value` does not work

gildor · Answer

ah you right I forgot that you want await for the first value just `ConflatedBroadcastChannel openSubscription receive ` than

Andrew Gazelka · Answer

wouldn t opening a new subscription each time be resource intensive

Andrew Gazelka · Answer

or it just seems weird probably just me tho

gildor · Answer

gt or it just seems weird It s not weird this stream of events you have to open it even if this stream is actually observable data

Andrew Gazelka · Answer

but you are opening it every time you need to poll a value

gildor · Answer

But careful you probably also want to close subscription so to make it a bit safer you can use flow instead ```ConflatedBroadcastChannel asFlow single or singleOrNull if you don t want to throw exception```

gildor · Answer

gt but you are opening it every time you need to poll a value edited yes but what do you expect Or you await it and than you need some primitive or you just get current value

gildor · Answer

I still not sure about your case but it s way how data streams work not only reactive

Andrew Gazelka · Answer

my use case is I have two websockets for data prices which is essentially an event driven and makes sense to use a `Flow` even though normally hot data but the web socket is created with a function so it is self contained and is still cold then I am using the two flows in another function which does period calculation given the current price the `Flow` is used for updates in price

gildor · Answer

gt period calculation given the current price You shouldn t use pull for this

gildor · Answer

or just wait for new data or request this data by doing force update just create a method for this

Andrew Gazelka · Answer

I am getting the data from a websocket and I do not control the API

gildor · Answer

So than you don t need any kind polling

Andrew Gazelka · Answer

however once I get the data from the event driven web socket I need to access it in a polling like way

gildor · Answer

why

gildor · Answer

if you want to cache use conflatedbroadcast channel + flow

Andrew Gazelka · Answer

the formula needs to request what the current last value of data is

Andrew Gazelka · Answer

yeah ^^^

Andrew Gazelka · Answer

using CBC and flow is fine

gildor · Answer

gt request what the current last value of data but you said that you cannot force request last data you do not control API

Andrew Gazelka · Answer

I am using a web socket then have a black box in my program which looks at data in my web socket and lets me request the last value

gildor · Answer

so what is problem with CBC flow and combineLatest

Andrew Gazelka · Answer

none I think

Andrew Gazelka · Answer

which is what I was trying to say don t think I was clear tho

gildor · Answer

ah sorry

gildor · Answer

I just thought that we discussing how to do that

gildor · Answer

Did you see kotlinx corotuines 1 3 release notes <https github com Kotlin kotlinx coroutines releases>

gildor · Answer

channelFlow is what you need to wrap webscoket

gildor · Answer

with `bufferSize = Channel CONFLATED` param

gildor · Answer

than use combine latest for 2 flows to get updates when one flows is changed using combineLatest <https github com Kotlin kotlinx coroutines issues 1193>

louiscad · Answer

Also < C1CFAFJSK|coroutines> slightly smiling face