Can I store a composable function in a variable?

Question

In Kotlin, function is a first-class citizen. We can store a function in a variable as below

val functionVariable: () -> Unit = ::myFunction

fun myFunction() { }

However, for @Composable function, how can I do so?

If I did the below, it will cry foul i.e. org.jetbrains.kotlin.diagnostics.SimpleDiagnostic@e93b05f8 (error: could not render message)

val functionVariable: () -> Unit = ::myFunction

@Composable
fun myFunction() { }

Is there a way to store composable function as a variable?

Answer 1

Composable function reference is not yet supported (and that's what the error message actually is). Besides, @Composable annotation is part of the function signature because it adds some parameters to the function. So you need to use val functionVariable: @Composable () -> Unit = { myFunction() }.

Answer 2

You can declare a composable function variable, like:

var functionVariable: @Composable () -> Unit = {}

Later you can reassign it (essentially redefining it) like:

functionVariable = { myFunction1() }

or

functionVariable = { myFunction2() }

But if you have functionVariable already planted in your larger Composable, the reassignment likely won't trigger recomposation. What I do is declare a state variable like:

var functionAssigned by mutableStateOf(0)

And in you larger Composable where you plant functionVariable, do:

if (functionAssigned >= 0) functionVariable()

And whenever you want to reassign the variable, do:

functionVariable = { myFunction2() }
functionAssigned++

That will trigger needed recomposation.