Hi folks, Compose 1.1.0 can’t seem to handle ?: with null values, doesn’t generate text on null inpu...

# compose

[Sam]

Hi folks, Compose 1.1.0 can’t seem to handle ?: with null values, doesn’t generate text on null input. It works fine in 1.0.5 with Kotlin 1.5.31

@Composable
fun Greeting(name: String?) {
    name?.let { Text(text = "Hello $name!") } ?: Text(text = "Hello!")
}

[Sam]

https://issuetracker.google.com/issues/219091191

[Rick Regan]

Is this the same as https://issuetracker.google.com/issues/198511576 ?

[Alexander Maryanovsky]

That's a weird way to use let and ?:

[Alexander Maryanovsky]

You realize the ?: is used on the value of the let expression? If the value of the last expression inside the let happens to be null the else part of the ?: will be executed.

[Chrimaeon]

It’s still a valid expression , @Alexander Maryanovsky although a if/else would be more readable in this case

[Alexander Maryanovsky]

It is, but it’s not clear whether the behavior a bug. What’s the result of the expression

name?.let { Text(text = "Hello $name!") }

if name is null?
On the face of it, it’s null, but actually it’s Unit. Not sure why, but there’s probably a good explanation.

[Alexander Maryanovsky]

Although there does seem to be something deeper here. If I replace Text(…) with println(…) it works as expected, and the result is null.

[Chrimaeon]

yes, because the elvis operator on the name and not the result of let

[Alexander Maryanovsky]

Yeah, looks like the compose compiler is inserting some additional code there which causes the result to be Unit

[Chrimaeon]

Ah, that’s what you mean. Okay!

[Alexander Maryanovsky]

But I’m seeing the same behavior with Compose 1.0.1 and Kotlin 1.5.31

[Michael Paus]

The observed behaviour may be a bug but would this code

@Composable
fun Greeting(name: String?) {
    Text(if (name != null) "Hello $name!" else "Hello!")
}

not be several times more readable and also less error prone (for the developer and the compiler)?

[Sam]

This usage of ?: was just for minimum steps, the actual usage in app involves additional logic within those blocks.

[Sam]

@Alexander Maryanovsky >> But I’m seeing the same behavior with Compose 1.0.1 and Kotlin 1.5.31

Different behavior at my end with 1.0.5 and 1.5.21, ?: works just fine

[Alexander Maryanovsky]

@Sam It doesn’t matter what additional logic is inside those blocks. Just replace them with an if … else …

[Sam]

Yeah using as a workaround for now, but seems to be regression for sure

[Alexander Maryanovsky]

Even if there was no compose bug here, you’re relying on the last statement in the let not returning null

[Alexander Maryanovsky]

Which is probably a bad idea

[Sam]

Wonder if there are any other tricky usage around nullable types that might fail at runtime

[Sam]

Sure, point taken but really crazy how plugin can break basic stuff