Hey, I've noticed that a change of value of `Mutab...

# compose

[marcinmoskala]

Hey, I've noticed that a change of value of MutableState leads to recomposition to all the composable functions that read this state, but I cannot find how exactly that is triggered.

Like in this simple code, clicks only cause "Recompose BodyReading" and "Value: true/false".

@Preview
@Composable
fun Recomposition() {
    val value = remember { mutableStateOf(false) }
    println("Recompose Recomposition")
    Button(onClick = { value.value = !value.value }) {
        Text("Click me")
    }

    BodyReading(value)
    BodyWriting(value)
}

@Composable
fun BodyReading(value: MutableState<Boolean>) {
    println("Recompose BodyReading")
    println("Value: ${value.value}")
    Text(" ")
    Text(" ")
}

@Composable
fun BodyWriting(value: MutableState<Boolean>) {
    println("Recompose BodyNotReading")
    value.value = false
    Text(" ")
    Text(" ")
}

In the compiled code, I do not see any essential differences, except that the first one has additional print and value.getValue() , while the other one value.setValue(false) . They both start startRestartGroup. My assumption is that getValue sets some listener for recomposition, but I cannot find that, and I would love to understand how that works.

[Stylianos Gakis]

If I understand your question correctly, you might enjoy reading this https://blog.zachklipp.com/restartable-functions-from-first-principles/
It contains links to the code where these things happen, like here https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:compose/[…]a071114c193cd7b43a05ba1489e72d21f3b833?ref=blog.zachklipp.com

[marcinmoskala]

Thanks, this is exactly what I was looking for. I suspected this line of code, but now I see how it works 👍