Hi guys, whats the negative points of doing that: ...

# coroutines

[Jhonatan Sabadi]

Hi guys, whats the negative points of doing that:

val state: StateFlow<String> = stateFlow(initialValue = "Loading...") {
        val result = getData("state")
        getAnotherData(result)
    }

    private fun <T> stateFlow(
        initialValue: T,
        dispatcher: CoroutineDispatcher = <http://Dispatchers.IO|Dispatchers.IO>,
        callback: suspend CoroutineScope.() -> T,
    ): StateFlow<T> {
        val scope = CoroutineScope(SupervisorJob() + dispatcher)
        val stateFlow = MutableStateFlow(initialValue)
        scope.launch(dispatcher) {
            stateFlow.update { callback() }
        }
        return stateFlow.asStateFlow()
    }

The idea is to “clone” liveData builder,

[kevin.cianfarini]

For one, unless you always explicitly pass in a dispatcher then this code won’t be properly testable since it has a static dependency on <http://Dispatchers.IO|Dispatchers.IO>.

[kevin.cianfarini]

If your callback is ever something that requires being unregistered on completion, then your abstraction has no way of unregistering. callbackFlow { … }.stateIn(scope, initial) would be able to invoke a cleanup when the channel gets cancelled and thus unregister your callback.

[Jhonatan Sabadi]

The idea is to have dispatcher as optional.
I was also thinking about of use ViewModel.stateFlow to use viewModelScope to launch coroutines

[kevin.cianfarini]

viewModelScope is now discouraged by Google because is has a static dependency on Dispatchers.Main and makes testing impossible without Dispatchers.setMain and Dispctahcers.resetMain.

[kevin.cianfarini]

A similar situation to your potential static dependency on <http://Dispcatchers.IO|Dispcatchers.IO>.

[kevin.cianfarini]

Oh also your function breaks structured concurrency

[kevin.cianfarini]

A better builder that avoids this problem would be something like:

private fun <T> stateFlow(
  initial: T,
  scope: CoroutineScope,
  callback: ProducerScope<T>.() -> Unit
): StateFlow<T> = callbackFlow(callback).stateIn(scope, initial)

But at this point the builder isn’t very useful when you could just call those two functions manually

[Jhonatan Sabadi]

Got it. The initial idea is to avoid boilerplate:

val state2: StateFlow<String> = flow<String> {
        val result = getData("state")
        getAnotherData(result)
    }.stateIn(
        scope = viewModelScope,
        started = SharingStarted.WhileSubscribed(),
        initialValue = "Loading..."
    )

[Jhonatan Sabadi]

Do you have an suggestion to avoid it?

[kevin.cianfarini]

If you're worried about the small amount of boilerplate, use the example I gave above.

[louiscad]

Boilerplate can almost always be simplified/moved as a function in Kotlin.