Hi, I fell into a little types mangling while doin...

# getting-started

[Ayfri]

Hi, I fell into a little types mangling while doing a library for Kotlin/JS, I typed some events types that uses eventemitter3 library with a pretty ugly (I think) but simple solution

sealed interface DisplayObjectEvents<T : Any> {
	object added : DisplayObjectEvents<Container>
	object click : DisplayObjectEvents<FederatedPointerEvent>
	object clickcapture : DisplayObjectEvents<FederatedPointerEvent>
	object destroyed : DisplayObjectEvents<Nothing>
	object mousedown : DisplayObjectEvents<FederatedPointerEvent>
    ...
	(there are almost 100 elements in total)
}

But I want to be able to use it like that myObject.on<DisplayObjectEvents.added> { // it is Container here } , so I created this

inline fun <reified T : DisplayObjectEvents<T>> DisplayObject.on(noinline callback: (T) -> Unit) = on(T::class.simpleName!!, callback as ListenerFn, null)
// ListenerFn is just a function type that take Any arguments Any number of time
// Which is the default type for my library for events in TypeScript

But

myObject.on<DisplayObject.added> {
    // it is of type DisplayObject.added
}

What I've done wrong ?

[Ayfri]

I've come up with a solution that requires an argument instead of reified type but if I can avoid it it would be nice

inline fun <T : Any> DisplayObject.on(event: DisplayObjectEvents<T>, noinline callback: (T) -> Unit) = on(event::class.simpleName!!, callback as ListenerFn, null)

myObject.on(DisplayObjectEvents.added) {
	// it is correctly of type Container
}

[Ruckus]

reified T : DisplayObjectEvents<T> means that T needs to be both a DisplayObjectEvents as well as its generic parameter. You could either pass in a parameter (as you've done) or have two generic types.

[Ruckus]

You should see some sort of bounds warning if you try on<DisplayObjectEvents.added>, since added has a generic of Container which does not fit the restriction T : DisplayObjectEvents<T>.

[Ruckus]

With two generics it would be something like

inline fun <reified D : DisplayObjectEvents<T>, T : Any> DisplayObject.on(noinline callback: (T) -> Unit) = on(D::class.simpleName!!, callback as ListenerFn, null)

And used like

obj.on<DisplayObjectEvents.added, Container> { ... }

But I personally think the extra parameter version you have is cleaner.

[Ayfri]

Yes I've seen these problem, and if I put two generic types it's asking me to declare both when using the method so I loose the utility of what I'm trying to do

I guess I'll stick with using a parameter