I recently read something that I interpreted as being bad ``

Question

I recently read something that I interpreted as being bad ``` suspend fun someFunctionCreatesAFlow context Dispatchers Default Flow lt String gt = withContext context flow emit somethingAsAString ``` I guess it is because Flows kinda manage their own context with `flow flowOn ` Can anybody confirm this

Dennis Schröder · Answer

So I guess this is the right way ``` suspend fun someFunctionCreatesAFlow context Dispatchers Default Flow lt String gt = coroutineScope flow emit somethingAsAString flowOn context ```

Dominaezzz · Answer

``` suspend fun someFunctionCreatesAFlow context Dispatchers Default Flow lt String gt = flow emit somethingAsAString flowOn context ```

Dennis Schröder · Answer

Ohh well yeah but in my actual use case `somethingAsAString`is of type `suspend CoroutineScope gt String` Therefore I need a scope

octylFractal · Answer

it s not bad necessarily but iirc `flow` isn t a suspend function itself only terminal operations so it doesn t pass any of the context to the flow technically that function doesn t need to be suspend at all

Dennis Schröder · Answer

But I forget to mention sorry

octylFractal · Answer

if you need a scope create it inside `flow `

octylFractal · Answer

e g ``` flow coroutineScope ```

louiscad · Answer

Don t make is suspending just use `flowOn`

streetsofboston · Answer

What Louis said The creation of a Flow has needs no context scope The collector of the Flow however does need one and that will be the same scope that is used when your Flow s emitter that suspend lambda is called

Pablichjenkov · Answer

If I call `Flow collect ` from a scope that has a Dispatcher UI type Will the flow chain process in this UI scope by default Am I forced to use `flowOn IOContext ` to make it execute off the UI thread

streetsofboston · Answer

< Pablichjenkov> That is not necessary a problem As long as you don t have blocking code in your Flow you should be all set If you have suspending code inside your Flow that is not a problem either since suspending won t block the UI thread

Pablichjenkov · Answer

Well by flow chain process I mean flows that have suspending functions inside and either IO or heavy computation blocks Where these suspending blocks will be executed if not passed any Dispatcher explicitly Dispatcher Default

louiscad · Answer

All the info about that is already in kotlinx coroutines docs You can verify what you see in the docs that should help you understand what to expect

octylFractal · Answer

flows run on the same dispatcher as whatever calls the terminal operations unless you use `flowOn` then everything setup before that call runs in the context passed there calls after `flowOn` still use the same dispatcher as the terminal op caller

Pablichjenkov · Answer

< octylFractal> I read what you just said however my concern was about the following You have 2 types of code in a flow lets say ``` case 1 flow suspendingBlockingFunc and case 2 flow nonSuspendingBlockingFunc Blocks either by IO or heavy CPU ``` If not using `flowOn` operator and calling `collect ` from Dispatcher UI Case 1 flow will execute on UI killing it Case 2 flow will execute on where gt Default

octylFractal · Answer

exactly what I said the same dispatcher as `collect `

octylFractal · Answer

that is case 1 amp 2 are the same there is no difference in how they are executed besides what the function they call does

Pablichjenkov · Answer

I see it now There is no magic behind it

Pablichjenkov · Answer

thnks