Should one include

companion object {}

in library classes to support extension?

Out of curiosity, what benefits does this give you?

Well for example, if my library has a class

Point

and I include

companion object {}

, a user of the library could define

fun Point.Companion.fromJson(json: String) = // ...

allowing them to do

val p = Point.fromJson(json)

oh, I see, it’s a way to allow for pseudo-class-static extension methods

Exactly

I’ve never considered that before, but I really like the idea!

Either I had until I was going through a similar example in class and I was like ya know that might be kinda handy

Hum, this is an interesting topic. If a third party class do not have a companion object, can we create a companion object extension for it?

Not that Im aware of

I was needing something like this to create some kotlin build scripts with kotlin dsl, this could be a good feature for us

I think the Arrow guys basically had a problem when Boolean didn't have a companion object for this exact reason. IIRC, the Boolean class got an empty companion object as a result.

I thought I vaguely recalled one of the "primitive" types not having one

You can use

companion object

without body if there's no declaration after it.

Hm. If you check

String

implementation in Kotlin it actually contains exactly this

companion object {}

.

@louiscad Intellij recommended that, required companion object; in most cases though

Yes, and now (as of 1.3.30 EAP), autocomplete no longer adds the braces