I think there was some discussion of this earlier ...

# compiler

[Rob Elliot]

I think there was some discussion of this earlier - is there any proposal to make anonymous objects have an associated type capturing their members?

[Rob Elliot]

I'd like to be able to type user.links.self and it compile for this class:

data class User(val id: Id) {
  val links = object {
    val self = "/v1/users/$id"
  }
}

[Rob Elliot]

As it is I'm doing this:

data class User(val id: Id) {
    val links = Links(
        self = "/v1/users/$id"
    )
    data class Links(
        val self: String
    )
}

which works fine but feels & reads slightly more laborious.

[hfhbd]

Or use an inner class:

data class User(val id: Long) {
    val links = Links()

    inner class Links {
        val self = "/v1/users/$id"
    }
}

Or an interface

[Rob Elliot]

That's less noisy, thanks.

[Emil Kantis]

If you want something composable.. maybe overkill.. I'm a big fan of how easy it is to compose behaviour with delegation 🙂

data class User(val id: Id): Linkable<Links.Self> by selfLink("/v1/users/$id")

interface Linkable<T : Links> {
  val links: T
}

sealed interface Links {
  data class Self(val self: String) : Links
}

fun selfLink(path: String) = object : Linkable<Links.Self> { override val links = Links.Self(path) }

[elizarov]

There was a similar discussion elsewhere recently, let me find it.

[elizarov]

Here is it https://kotlinlang.slack.com/archives/C0B9K7EP2/p1667308006940719

[elizarov]

That was about "inner object".

[elizarov]

Maybe we should support "inner object", indeed.

[Rob Elliot]

Thanks, sorry my searching was weak.

[Rob Elliot]

And I am in the wrong channel... apologies

[efemoney]

Fully onboard with inner object 🐕 Looking forward to seeing it in a coming features survey

[elizarov]

https://youtrack.jetbrains.com/issue/KT-16970/inner-object

[elizarov]

Add your use-cases that that issue, please.

[gildor]

I believe there is also discussion about case when you don’t necessary need internal object, but just an exposed object like:

object Dependencies {
   val ktor = object {
           val core = …
           val auth = …
   }
}

to allow use it like Dependencies.ktor.auth

It’s probably has the same issues as internal in terms of that it requires some object name generation. I would be probably would be fine if it would be required to use named object like:
val ktor = object Ktor {}
So no class name generation requied

[elizarov]

Exposing object also requires us to generate a stable class name under the hood. And the rules on how this name is derived and when you can count on it being stable are going to be quite complicated. From this angle, it looks easier to simply support inner object for such a use-cases.

[gildor]

Ah, indeed, inner object a lot easier because of jvm internal classes convention, yeah, for case which I shared above inner class also perfectly works