<@U33H6SB2B> with the new changes to typed arrays ...

# javascript

[Edoardo Luppi]

@turansky with the new changes to typed arrays in kotlin-wrappers, I'm stuck at trying to find a solution to my typealiasing.
See https://youtrack.jetbrains.com/issue/KT-60561/K2-cant-instantiate-expect-class-with-an-actual-class-that-has-type-arguments#focus=Comm[…]1204608.0-0

Basically I'm currently using

// commonMain
public expect class ZByteArray(size: Int)

// jsMain
public actual typealias ZByteArray = Uint8Array

However, with the new types it is required to specify a generic parameter

// jsMain
public actual typealias ZByteArray = Uint8Array<ArrayBufferLike>

Which then doesn't compile anymore.

The ZByteArray typealias is then used in exported classes/interfaces. For example

@JsExport
public interface ZOutputStream {
  public fun writeBytes(bytes: ZByteArray)
}

and that means subclassing Uint8Array<ArrayBufferLike> isn't a solution.

Note that while the kotlin-wrappers way emulates TypeScript, TypeScript also uses a default generic type, which isn't possible in Kotlin.

interface Uint8Array<TArrayBuffer extends ArrayBufferLike = ArrayBufferLike>

[turansky]

As workaround:

// jsMain
@JsName("Uint8Array")
public actual open external class ZByteArray(size: Int) : Uint8Array<ArrayBufferLike>

?

[turansky]

Or probably better solution - value class

[Edoardo Luppi]

public actual open external class ZByteArray

this version is then incompatible with other kotlin-wrappers types like Buffer

sealed external class Buffer : Uint8Array<ArrayBufferLike>

[Edoardo Luppi]

Managed to get it to compile with a bunch of unsafeCast<Buffer> and unsafeCast<ZByteArray>. Not ideal but it's a first step.

[turansky]

value class - isn't variant?

[Edoardo Luppi]

Mmm but how would I @JsExport signatures that use the value class?

[Edoardo Luppi]

What about adding additional types like (name is just a guess)

@JsName("Uint8Array")
external class UUint8Array : Uint8Array<ArrayBufferLike>

Than UUint8Array could replace all usages of Uint8Array<ArrayBufferLike> to mimic the default generic type.

[turansky]

image.png

[turansky]

Additional local type as workaround - my initial suggestion, which you rejected ;)

[Edoardo Luppi]

That's what I'm using as of now, with a bunch of unsafeCast. Since typed arrays are also used under kotlin-nodes types, every interaction with them requires an unsafeCast.