I don t seem to get ` Immutable` to work correctly for me wh

Question

I don t seem to get ` Immutable` to work correctly for me why do my list items recompose when changing only a `isLoading` flag of my UI State point right Code in thread

Steffen Funke · Answer

```typealias Items = List lt String gt ViewModel class RecomposeDemoViewModel repo DummyRepo = DummyRepo Immutable data class UiState val items Items = emptyList val isLoading Boolean = false val error Error = null var uiState by mutableStateOf UiState items = repo sampleData fun changeSomeUiState uiState = uiState copy isLoading = uiState isLoading My Root View Composable fun RecomposeDemo val viewModel by remember mutableStateOf RecomposeDemoViewModel LogCompositions Root Column Text This demo uses a monolithic state data class val uiState = viewModel uiState Header Row if uiState isLoading CircularProgressIndicator Button onClick = viewModel changeSomeUiState Text text = Toggle Loading State Why do list items in this LazyColumn recompose MyColumn items = viewModel uiState items Custom Lazycolumn to narrow recomposition scope premature optimization Composable fun MyColumn items Items modifier Modifier = Modifier LogCompositions tMy LazyColumn LazyColumn modifier = modifier fillMaxWidth items items item gt LogCompositions t t$ item Text item modifier = Modifier padding horizontal = 16 dp vertical = 36 dp Divider ```

Steffen Funke · Answer

This picks up on this Twitter discussion I don t think the list items should recompose at all when changing only a portion of the UI State What am I missing here Btw I am logging recompositions with the fine `LogCompositions` composable taken from this blog

Steffen Funke · Answer

Output on each Button click which only changes `isLoading` `items` stay the same ```Root gt gt Compositions 1 My LazyColumn gt gt Compositions 1 Item 0 gt gt Compositions 1 Item 1 gt gt Compositions 1 Item 2 gt gt Compositions 1 Item 3 gt gt Compositions 1 Item 4 gt gt Compositions 1 Item 5 gt gt Compositions 1 Item 6 gt gt Compositions 1 Item 7 gt gt Compositions 1 gt gt Button click Root gt gt Compositions 2 My LazyColumn gt gt Compositions 2 Item 0 gt gt Compositions 2 Item 1 gt gt Compositions 2 Item 2 gt gt Compositions 2 Item 3 gt gt Compositions 2 Item 4 gt gt Compositions 2 Item 5 gt gt Compositions 2 Item 6 gt gt Compositions 2 Item 7 gt gt Compositions 2 ```

Albert Chang · Answer

You are probably misunderstanding ` Immutable` If the class of a composable function parameter is marked with ` Immutable` or ` Stable` and it `equals ` the previous parameter then the function can be skipped You are not using `UiState` as the parameter of any composable functions and you are changing it at the first place so its stability is irrelevant here Recomposition is because `Items` is not stable

Steffen Funke · Answer

Yes but I have also while debugging annotated `Items` which btw is only a typealias to `List lt String gt ` should have made it clear with ` Stable` or ` Immutable` and no change There is an ongoing discussion in the Twitter Thread about this experiences Probably we are something missing Basically it boils down to why does the list recompose if the inputs have not changed

Steffen Funke · Answer

Probably related SO post <https stackoverflow com questions 69137265 jetpack compose stable listt parameter recomposition>

Albert Chang · Answer

I don t think marking a typealias has any effect You have to create a wrapper class if you want to mark the list as stable

Steffen Funke · Answer

Hm let me try that

Steffen Funke · Answer

I think I read in some conversation that we can should explicitely mark a `val` of type `List lt T gt ` as ` Immutable` for that reason Which has not had any effect

Albert Chang · Answer

Also note that this approach is not always more efficient <https kotlinlang slack com archives CJLTWPH7S p1631197442113000 thread ts=1631190058 097700 amp cid=CJLTWPH7S>

Steffen Funke · Answer

< Albert Chang> Wrapping the items into an ` Immutable data class` works indeed ``` Immutable data class Items val items List lt String gt class RecomposeDemoViewModel val repo DummyRepo = DummyRepo data class UiState val items Items = Items emptyList val isLoading Boolean = false val error Error = null var uiState by mutableStateOf UiState items = Items repo sampleData ``` Now I only get the recompositions I expect ```Root gt gt Compositions 0 My LazyColumn gt gt Compositions 0 Item 0 gt gt Compositions 0 Item 1 gt gt Compositions 0 Item 2 gt gt Compositions 0 Item 3 gt gt Compositions 0 Item 4 gt gt Compositions 0 Item 5 gt gt Compositions 0 Item 6 gt gt Compositions 0 Item 7 gt gt Compositions 0 gt gt Button Click Root gt gt Compositions 1 gt gt Button Click Root gt gt Compositions 2 gt gt Button Click Root gt gt Compositions 3``` Yay Thank you < Albert Chang>

Steffen Funke · Answer

For anyone interested I have created a public working Compose Desktop gist here <https gist github com sfunke b9f9cdcd8f02429819ec7d39e1d514bd> Still not sure if it is intented behaviour or if `List lt T gt ` should not behave immutable as well wenn annotated with ` Immutable`

Albert Chang · Answer

`List lt T gt ` is not immutable by nature it is read only And you can t annotate a class which is not in your control typealias won t work because it s not a class

Steffen Funke · Answer

Found the related threads with discussions So I can think we can close this here thank you

Orhan Tozan · Answer

< Albert Chang> what about kotlinx immutable ImmutableList

Albert Chang · Answer

< Orhan Tozan>

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

You could also use SnapshotStateList which is mutable but also stable and uses the immutable list that Orphan suggested under the hood