is there a way I can define a `NULL` as a companion object of an inline class using a type parameter...

# getting-started

[elect]

is there a way I can define a NULL as a companion object of an inline class using a type parameter?

@JvmInline
value class Ptr<T>(val adr: Adr = 0L) {
    companion object {
        val NULL: Ptr<*>
            get() = Ptr(MemoryUtil.NULL) // Not enough information to infer type variable T
    }
}

[gildor]

Ptr(MemoryUtil.NULL) -> Ptr<Nothing>(MemoryUtil.NULL)

[gildor]

or Ptr<*> to Ptr<Nothing>

[gildor]

I actually think that Null: Ptr<Nothing> is better, I don’t know how you are using T in this class, but probably there is no way to get anything from Null pointer, so Nothing is a good way to use Notning type here

[elect]

I'm basically extending them with primitives and java class of the corresponding C structs, ie
Ptr<Byte> or Ptr<VkInstance>

[elect]

your solution compiles fine, but if I try to use it, then I get an error

val a: Ptr<Byte> = Ptr.NULL

[elect]

Type mismatch.

Required: Ptr<Byte>

Found: Ptr<*>

[elect]

I guess there is no way? I also tried to extend it on the Ptr<Byte>.Companion but it's not possible, no companion

[elizarov]

You should declare the class as Ptr<out T>, then it’ll work with Nothing.

[elect]

Thanks, it does work indeed
Any contraindications with out?

[gildor]

Not really, looks that your case is a classic case of producer-object, official doc is pretty good in explanation of this:
https://kotlinlang.org/docs/generics.html