Hi all :android-wave:, I have a query regarding `m...

# compose-android

[Abhimanyu]

Hi all 👋,
I have a query regarding mutableState .

From the docs (https://developer.android.com/develop/ui/compose/state#state-in-composables),
I see that I can create a mutableState using either of these syntax.

var id: Int? by remember {
  mutableStateOf(null)
}
val setId = { updatedId: Int? ->
  id = updatedId
}

OR

val (id: Int?, setId) = remember {
  mutableStateOf(null)
}

I want to pass the method setId to function that has the method signature as setId: (Int?) -> Unit .

The first syntax where the setId was manually created by me has the required method signature as expected, but the setter method in the second syntax has the method signature as (Nothing?) → Unit .
So, I am getting a data type mismatch error.

Can anyone please share why this happens, and what is the best way to do this? thank you color

[Stylianos Gakis]

You might wanna specify the generic type on your mutableStateOf call instead, so mutableStateOf<Int?>(null). Or even use mutableIntStateOf instead.

With that said, I'd personally suggest to never use the destructuring syntax anyway, it's inferior to the delegate option for various reasons.

[vide]

^ The type is only inferred from the value you pass to mutableStateOf. For example

val id: Int? = mutableStateOf(null)

won't work either.

[Abhimanyu]

With that said, I'd personally suggest to never use the destructuring syntax anyway, it's inferior to the delegate option for various reasons.

So, the suggestion is to always use the first syntax and manually create the setters?

[vide]

You might not need a named setter at all depending on the use case. My team also mostly prefers not to use delegates either for explicitness

[Stylianos Gakis]

The [get, set] syntax has the negative that you're doing the state read right there and then. You are not allowing yourself to take the free wins of sometimes reading the new state from inside a smaller recomposition scope.
Plus you are making it impossible to do this https://developer.android.com/develop/ui/compose/performance/bestpractices#defer-reads since even if you then pass () -> State, you've read the state at declaration.

[vide]

I find it somewhat interesting that the deconstruction syntax is present in the docs without further context. Furthermore it's even written that

These declarations are equivalent

[Abhimanyu]

The equivalent part was the main source of confusion.

[Stylianos Gakis]

They are and should be the same when it comes to correctness, just not performance.