I currently have these modifiers:

fun Modifier.impression(
    id: String,
): Modifier = composed {
    Logger.v(tag = "ImpressionTracking") { "Creating modifier($id)" }
    LaunchedEffect(key1 = id) {
        Logger.v(tag = "ImpressionTracking") { "Launching effect($id)" }
    }
    this
}

fun Modifier.placeholderBackground(): Modifier =
    this then background(Color(0xFF272727))

Example usage (my case is actually more complex but I think this is the minimum case):

Box (
    modifier = Modifier
        .impression("1")
        .placeholderBackground()
)

That

LaunchedEffect

gets launched multiple times on recomposition. If I remove

then

from

placeholderBackground

:

fun Modifier.placeholderBackground(): Modifier =
    this.background(Color(0xFF272727))

Then it only gets launched once. It seems

composed

is not keeping state. I found this issue https://issuetracker.google.com/issues/270963071, but my case is with

then

on other modifiers. In the end it can possibly be the same issue. But this seems like a footgun that is not obvious at all.

Now I don’t know much about the implementation details, but it seems with

then

it duplicates the modifiers that were before into two different paths and ends up materialising

composed

twice, If I have more modifiers with

then

, it creates more paths and more

composed

materialisations, one “state” for each possible path on the tree. And why does removing

then

solve it, when predefined modifiers also use it?

So why does

this then Modifier.background(...)

work? … Look at the source of

Modifier

’s companion object is which is the empty

Modifier

, you can see that its

then

method, short circuits to the other modifier

Thank you for answering!

I guess a lint check could really be useful here