WTF?

# announcements

[Pitel]

WTF?

[gildor]

What is declaration of PageStore?
I believe it like:

class PagedStore<T>(value: T)

But should be

class PagedStore<out T>(value: T)

[Dominaezzz]

What?

[Dominaezzz]

What's the signature of pager?

[gildor]

Probably like

fun pager(store: PagedStore<List<*>>)

[Pitel]

class PagedStore<T : List<*>>( ... )

[Pitel]

fun RenderContext.pager(pagedStore: PagedStore<List<*>>) { ... }

[gildor]

It’s quite strange declaration

[gildor]

So this pagedstore is not preserve any types of list?

[gildor]

If so, you need something like this:

class PagedStore<out T : List<*>>(value: T)

[Fleshgrinder]

Or cast on the call site.

[gildor]

no need to cast on call site

[gildor]

it’s completely valid case and it can be solved by setting correct covariance

[Pitel]

The out doesn exactly help.

[gildor]

So it’s not type safe in you case

[gildor]

and it also have sense

[Pitel]

I cant't change the implementation of RootStore, btw.

[gildor]

How RootStore is declared?

[Pitel]

https://github.com/jwstegemann/fritz2/blob/master/core/src/jsMain/kotlin/dev/fritz2/binding/store.kt#L195

[gildor]

if you need invarience, you just cannot safely pass it

[gildor]

it’s common problem of data containers

[gildor]

You can do nothing without changing root implementation

[gildor]

For example check declaration of kotlin.collections.Collection, it has out to be covariant, but also it still has unsafe invarience (but it safe for cases where it used):

public operator fun contains(element: @UnsafeVariance E): Boolean

[Pitel]

I'll have to better understand the in/out keywords...

[gildor]

So in this case only unsafe cast will help, as @Fleshgrinder suggested

[gildor]

If you can chenage pager() decalaration, you can set it to something like:

fun pager(store: PagedStore<out List<*>>)

So it will be possible to pass any List there, but you still have to do unsafe cast inside (though, it will not be unsafe)