Organizing extensions in Kotlin - swift

Question

In Swift we usually use extensions as a way to organize methods in separate blocks and even files. This makes code much cleaner but it also allows us to do some tricks such as:
class API {}
extension API {
class Lists{}
}
extension Lists {
class Posts {
func latest() -> [Post] {
// get latest posts from a REST api
}
}
}
We can put any of the extension blocks in a separate file and it works perfectly in Swift.
Now one do the following to get the latest posts from the API in a clean way
let posts = API.Lists.Posts.latest()
Trying to convert that code into Kotlin I used SwiftKotlin converter tool that I thought that might work but it doesn't compile as It seems to be invalid:
class API {}
class API.Lists {}
class Lists.Posts {
companion object {
fun latest() {
// get posts
}
}
}
So I came up with the following that works fine and also compiles but it's not suitable for my case as methods can be quite long and I can't afford to have them all in one class in one file and I don't know how I can split them in multiple files.
class API {
class Lists {
class Posts {
companion object {
fun latest() {
}
}
}
}
}
Any suggestion is appreciated.

Answer 1

To put an extension on a companion object, you can write
fun API.Lists.Posts.Companion.latest() ...
You still need
class API {
class Lists {
class Posts {
companion object {
}
}
}
}
in a single file, but extensions can be defined elsewhere.

Answer 2

If you just want to mimic usage of these calls, you can use objects, like this for example:
object ApiPosts {
fun latest() {}
}
object ApiLists {
val Posts = ApiPosts
}
object API {
val Lists = ApiLists
}
API.Lists.Posts.latest()
But this is really not a Kotlin way, and in common case it's a bad practice to write in a language the way it's not supposed to.

Answer 3

One possible solution is to just extend the inner classes with normal functions not static ones (companion):
class ParentClass {
class InnerClass {
}
}
And in any other file you could do:
fun ParentClass.InnerClass.instanceMember() {
}
And for usage:
ParentClass.InnerClass().instanceMember()
Of course this isn't exactly like the Swift version but it's close enough.