I have a data class with some nullable `val` prope...

# general-advice

[Zyle Moore]

I have a data class with some nullable val properties. It's defined in a core module. I'm using it in a web module. Sometimes it can be smart-cast to its non-nullable version, but other times it can't. I thought that if I wrap usage in an if (nullableProp != null) { doSomethingWith(nullableProp.toString()) }, it would be safe, but it's not. Browsing for answers points to cases where it's a var, which could be reassigned between dereferencing calls. Or, the other module can be recompiled(?) and not be nullable anymore. But surely, a simple data class with `val`s is safe, right?
I was able to swap a `forEach`'s it with the deconstructed props, and it works fine then, so it seems like it's related to dereferencing it more than once, since deconstructing (having a single variable for the property) can smart cast, even though it's still a Public API in a different module

[Zyle Moore]

Oh, I guess you could have a data class with a nullable property that flip flops values in the same instance, right? Like

data class Something(val somethingStatic: String) {
    val flipFlop: String?
        get() =
            if (randomInt().even) { somethingStatic }
            else { null }
}

Is that why?

[CLOVIS]

Yes, it's one of the cases

[CLOVIS]

The main solution is simply to create a local variable, replace

if (foo.nulableProp != null) {
    doSomethingWith(foo.nullableProp)
}

by

val nullableProp = foo.nullableProp
if (nullableProp != null) {
    doSomethingWith(nullableProp)
}

This way, the smart-cast works

[CLOVIS]

Another case that breaks this is if in a future version you change the val to a var , it's also not safe to smart-cast anymore