Is there any difference in ```suspend fun getFlow = withContext <http Dispachers IO|Dispachers IO> flow ``` and ```fun getFlow = flow flowOn <http Dispachers IO|Dispachers IO> ```

ohh got it so I guess the equivalent function of flowOn will be ```suspend fun getFlow = flow withContext Dispatchers IO ```

Is there any difference in ```suspend fun getFlow = withCont kotlinlang #coroutines

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Title

# coroutines

Juan Rada

10/26/2023, 9:37 AM

Is there any difference in :

Copy code

suspend fun getFlow() = withContext(<http://Dispachers.IO|Dispachers.IO>) {
     flow { ... }
}

and

Copy code

fun getFlow() = flow { ... }.flowOn(<http://Dispachers.IO|Dispachers.IO>)

Joffrey

10/26/2023, 9:38 AM

Yes, the first one doesn't make sense, and doesn't do what you think it does

In the first example,

withContext

will only affect the creation of the flow (which is very quick because it doesn't execute the body of the

flow

builder). It will suspend the caller and potentially do a context switch just for an instant, just the time it takes to instantiate a flow and return it. Only the flow instantiation and the return will be executed in the IO dispatcher.

In the second example, the caller is not suspended at all, a flow is constructed immediately, and the body of the flow itself will be executed on the IO dispatcher when the flow is collected. The creation of the flow and the return are executed in the caller's thread

Juan Rada

10/26/2023, 9:46 AM

ohh got it so I guess the equivalent function of flowOn will be

Copy code

suspend fun getFlow() =  flow {
    withContext(Dispatchers.IO) {  }
}

👎 1

Mikhail

10/26/2023, 10:09 AM

flowOn

affects not only

flow {}

block but also any

map

transform

and similar functions in chain before

flowOn

call. In your example behavior will be the same, but if you add

map

between

flow {}

and

flowOn

behavior will become different

👍 2

Peter Farlow

10/26/2023, 1:54 PM

Generally, do not use

withContext

inside the

flow { }

flow builder. If you try to call

emit

inside the

withContext

block, it will throw an exception. You should use flowOn if you want to change the dispatcher on which the flow executes the code

myanmarking

10/26/2023, 1:57 PM

i don’t think withContext will do anything really, i might be wrong. There is no suspension point in the function

Peter Farlow

10/26/2023, 2:04 PM

I had assumed that code was omitted for brevity

➕ 2