this bit of code never prints 1 in console Does recomposer c

Question

this bit of code never prints 1 in console Does recomposer conflate values ```fun main var state by mutableStateOf value = 30 application Window Button onClick = state = 1 state = 2 println got $state Text state ``` Debugger shows that shapshot system sees all values but `recompositionRunner` never receives the 1 value Are there some optimizations in `Snapshot apply` method maybe What should one do to receive all state updates or is this impossible wrong

Zach Klippenstein (he/him) [MOD] · Answer

Changing a mutable state read by a composition only schedules a recomposition to happen before the next frame Any number of changes to any number of state objects can happen before then

Zach Klippenstein (he/him) [MOD] · Answer

It is indeed a bit wrong to try to force something to see all state updates States should be idempotent

dimsuz · Answer

I see thank you for clarification

dimsuz · Answer

We have this curious situation imagine entering pin code and then requesting to enter it again to confirm for each pin digit we display a filled dot When user fills all dots of 1st pin UI switches to new pin state fresh empty And this state change happens so fast that user doesn t see the last dot filled it goes from ` o` gt `oooo` while state goes ```digits = 1 1 1 0 digits = 1 1 1 1 digits = 0 0 0 0 ``` last two get conflated because as you ve explained they fit into one frame update While we would like that user would see all three states rendered including the fully filled one I wonder what would the correct solution be here We could always add some arbitrary delay but this doesn t feel right

dimsuz · Answer

< Adam Powell> ^^^ I recall that maybe you had once explained something about these cases but don t remember exactly what Isn t this somehow related to states vs events discussion

Alex Vanyo · Answer

gt we would like that user would see all three states rendered including the fully filled one How long would you want the user to see the fully filled state

Zach Klippenstein (he/him) [MOD] · Answer

yea this sounds like a question for your designer Animation could help here

Alex Vanyo · Answer

Also my question is meant to be leading smile since my follow up question will be this If you want the user to see the fully filled state for say 500ms what happens if they enter the first digit of the pincode after just 200ms Then what do you want to be displayed

dimsuz · Answer

Yeah in the end we devs seem to came to the same conclusion that this evidently needs some animation delay because this isn t anymore strictly about the data state but also about interaction state Initially this has tricked us because the fill events came from user pressing keys but the last one triggers the transition which is programmatic but we want it to feel interactive Not sure if I explain myself correctly slightly smiling face

dimsuz · Answer

gt what happens if they enter the first digit of the pincode after just 200ms right I ve also thought in this direction that if this has to be a delay it has to be smart slightly smiling face

Alex Vanyo · Answer

I think there s a nifty approach here involving `MutatorMutex` ```class PasscodeState var firstDigit by mutableStateOf false private set var secondDigit by mutableStateOf false private set var thirdDigit by mutableStateOf false private set var fourthDigit by mutableStateOf false private set private val mutatorMutex = MutatorMutex suspend fun inputDigit mutatorMutex mutate if firstDigit firstDigit = true else if secondDigit secondDigit = true else if thirdDigit thirdDigit = true else fourthDigit = true try delay 500 finally firstDigit = false secondDigit = false thirdDigit = false fourthDigit = false ```

Alex Vanyo · Answer

How that works is there can only be at most one instance of the `block` passed to `MutatorMutex mutate` running at a time Just like a normal mutex it is guarding setting any of the digit state `MutatorMutex` also has the feature that a second call while there is an existing one running will cancel the old call the priority controls exactly when So in this case when we set the fourth digit to true we plan to reset them all after 500 milliseconds If another input comes in earlier the `finally` triggers first resetting the state before the new input runs and sets the `firstDigit` to `true` again

Adam Powell · Answer

suspend is so much more fun once you realize it s a language feature for generating arbitrary state machines smile

Adam Powell · Answer

And yeah this is related to the states vs events space Zach started another internal discussion in response to this thread too and the topic of the `InteractionState` API came up we modeled that as an event stream designed to reduce state specifically to enable this sort of thing lingering pressed states etc though we aren t leveraging a whole lot of it today

Adam Powell · Answer

the code for handling press states for Views is kind of complicated and annoying for all of these same reasons

dimsuz · Answer

Thank you all for the input Fisrt time I ve heard about `MuatatorMutex` will study it and that finally trick is cool Yeah suspend functions are the state machines underneath aren t they slightly smiling face I guess first we learn to forget this abstraction but then we learn about it on kind of a new layer