```data class Car(val name: String) @Composable private fun Test() { var car by remember { muta...

# compose

[theapache64]

data class Car(val name: String)

@Composable
private fun Test() {
    var car by remember { mutableStateOf(Car("Audi")) }
    var remCar = remember { car }
    LaunchedEffect(car) {
        remCar = car
    }
    println("remCar is `${remCar.name}`")
    Button(
        onClick = {
            car = Car("BMW - ${System.currentTimeMillis()}")
        }
    ) {
        Text("CHANGE CAR")
    }
}

Pressing CHANGE CAR button always prints remCar is Audi

Why it’s not printing BMW ? 🤔

[jw]

Because you remember a value that is captured once

[jw]

You need to use derivedStateOf

[jw]

or add car as a key to the second remember

[jw]

oh i missed the LaunchedEffect, but it's not a State so writes to it presumably won't trigger recomposition

[theapache64]

Yeah, but it should print BMW for the next recomposition, right?

[jw]

It will not because when the function re-runs the remember will re-read the original car value from the slot table and it will always reset to the Audi

[theapache64]

Ooo 😮 So basically, we can’t change a remember -ed value like this

[jw]

That's right. Because it's basically a positional marker into a separate storage mechanism. All you do when you overwrite the local is overwrite the value that was read. You do not overwrite the backing storage location.

[Kevin Del Castillo]

It won't work because changing the value of remCar is not actually changing the value of the mutableStateOf , that's a misconception because the setter of car is not actually just setting a variable but updating the state, also you don't need to remember car , it's been already remembered.

[jw]

When you remember a State the backing storage contains a reference to the State instance rather than a raw value. This is why changes to the State are reflected on future recompositions. The remember reads out the same State instance each time but the value held by that State is what changes.

[theapache64]

Ohhkay.. Understood. Thank for the explanation guys 🙌