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#compose
Title
# compose
a

Alexander Maryanovsky

11/04/2023, 8:33 AM
Why doesn’t 
Modifier.testTag("42")
cause a recomposition of the function it’s passed to, but 
Modifier.testTag(functionThatReturns42())
does?
This prints “(Re)composing MyText” twice:
Copy code
@Composable
private fun MyText(
    modifier: Modifier
) {
    println("(Re)composing MyText")
    Text("Hello", modifier = modifier)
}

private fun makeTestTag(): String {
    return "42"
}


fun main() = singleWindowApplication {
    var number by remember { mutableStateOf(1) }
    Column {
        Text("$number")
        MyText(
            Modifier.testTag(makeTestTag())
        )
    }
    LaunchedEffect(Unit){
        delay(2000)
        number += 1
    }
}
But if I replace 
makeTestTag()
with 
"42"
it prints it only once.
wow, it prints it twice even if 
makeTestTag
is inline!
That has got to be a bug in the compose compiler, no?
a

ascii

11/04/2023, 8:49 AM
Maybe comparison is 
===
? "42" is constant; function is evaluated every time 
number
changes, thus returns a new string every time.
even if 
makeTestTag
is inline
hmm no idea
a

Alexander Maryanovsky

11/04/2023, 8:51 AM
“42” is an interned constant regardless of where it appears. At least that’s how it is in Java.
But regardless, I don’t think it should compare references.
s

shikasd

11/04/2023, 6:15 PM
"42" is inferred to be static (const), and modifier testTag has stable annotation on it, so if expression you pass there is constant, we infer it as never changing in the second case, modifier is not inferred as static because of the function call, so new instance of modifier causes recomposition. to fix this, consider hoisting modifier to the scope that does not recompose, or you can technically try applying @stable to the function that returns const value
a

Alexander Maryanovsky

11/04/2023, 6:18 PM
Ah, I forgot functions could also be marked as 
@Stable
. Yeah, that solves it.
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