How do you 'remember' something which could be nul...

# compose-desktop

[v79]

How do you 'remember' something which could be null (and probably will be initially?). I.E. can you remember a class, but not an instance of it? var something = remember { mutableStateOf<MyClass>(_* can't construct here because it's currently null *_) } ?

[Eric Chee]

I would suggest a sealed class. Therefore you eliminate the use of null all together

[Big Chungus]

mutableStateOf<MyClass?>(null)

[v79]

I don't think a sealed class is going to work; I'm trying to make something very generic. Martynas's suggestion seems to be working.

[v79]

Though of course, I've hit my next snag...

[v79]

I don't Compose likes generics very much.

[Eric Chee]

sealed class State {
   object Loading: State()
   class Ready(val myClass: MyClass): State()
}

// your code
val nullableFoo = ...
var state = remember { mutableStateOf<State>( 
   if (nullableFoo != null) Ready(MyClass(nullableFoo)) else Loading
)}

when (state) {
   is Loading -> // show loading component
   is Ready -> state.myClass.... // show some component with state.myClass
}

[Eric Chee]

a sealed class should work with generics. its commonly used with like Results

sealed class Result<out T : Any> {
    data class Success<out T : Any>(val data: T) : Result<T>()
    data class Error(val exception: Exception) : Result<Nothing>()
}

[Big Chungus]

sealed class Nullable<T>(val value:T) {
abstract val isPresent: Boolean
object Null: Nullable<Never>(null) {
override val isPresent = false
}

class Present<T>(value: T): Nullable(value) {
override val isPresent = true
}
}

[v79]

Thanks, I'll take a look. I'm at that stage where I've got about 12 possible solutions and need to step back and think!

[Big Chungus]

mutableStateOf<Nullable<MyType>>(Nullable.Null)

[Big Chungus]

Although I prefer nullable MyClass? type over this

[v79]

For now I've done

mutableStateOf<FontModel?>(null)

[v79]

Have you ever worked with fonts? Confusing things. I've got 3 different import aliases to distinguish between different Font classes (and a Compose function called Font).