Trying to have enums backed by an `IntBuffer`, I'm...

# announcements

[elect]

Trying to have enums backed by an IntBuffer, I'm writing an extension function for an Enum, where its companion object extends a specific interface. But if I cast, the compiler says the cast can never succeed.. why?

fun <E> Enum<E>.bind() where E : Enum<E>, E : A = (Enum.Companion as B).buffers[ordinal].bind() // this cast can never succeed

[Sam Schilling]

Also don’t you need to put the return type of the function before the where clause?

[elect]

this fails Enum.Companion as B

[elect]

it's Unit

[Sam Schilling]

oh I see I misread that

[jw]

Because that refers to the companion of the Enum class, not the companion of the receiver

[elect]

is there a way ro retrieve the receiver companion?

[Ruckus]

There is no way in the type system to specify "a class that has a companion object" (let alone of a specific type)

[Dominaezzz]

A decent compromise is to replace Enum<E> with an interface that can return it's "companion object". Won't be type safe but .... it works 😅.

[Ruckus]

Or change bind to accept a B

[elect]

@Dominaezzz problem is that then the buffers would be static per interface. I need to have them per enum.
Because I'd like to have the possibility to have multiple enums (extending the same interface) backing each different objects

[Dominaezzz]

From the interface you decide what object you want to return,

[elect]

can you elaborate @Dominaezzz?

[elect]

@Ruckus, let me show you a gist: https://gist.github.com/elect86/641c6c2f82a9896edef49a270b545ae2

[Ruckus]

That gist has several problems with generics

[Dominaezzz]

GlBufE can have a method that returns an instance of GlBufEco.

[elect]

yeah yeah, it's just a draft

[Ruckus]

Sorry, I only meant I don't understand what each placeholder is supposed to do as the generics don't line up. But I'd go with @Dominaezzz's suggestion if it makes sense (you'd probably have to change the function to fun <E> E.bind(... instead of Enum<E>.bind(...)

[Ruckus]

Maybe something like this: https://pl.kotl.in/7LQEa_sRz
(Assuming I didn't totally screw up the generics)

[Dominaezzz]

Tiny upgrade, T : Enum<T>.

[Ruckus]

Wouldn't that make bind infinitely recursive?

[Dominaezzz]

Oh nvm. I just had another look at the signature of bind.

[Dominaezzz]

Should bind just be a member at this point.

[elect]

@Ruckus interesting if I write: fun <T> T.bind(target: BufferTarget) where T : Enum<T>, T : GlBufE = T.buffers[ordinal].bind(target) I get:

Error:(182, 70) Kotlin: Type parameter 'T' cannot have or inherit a companion object, so it cannot be on the left hand side of dot

[elect]

sorry, I'm an idiot: fun <T> T.bind(target: BufferTarget) where T : Enum<T>, T : GlBufE = buffers[ordinal].bind(target)

[elect]

@Dominaezzz a member of what?

[Dominaezzz]

Nvm