A modern programming language that makes developers happier.

kotlinlang

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

And while I haven't created any myself I was giving a lecture on companion objects this week and it got me thinking that maybe I should include empty ones to allow for this

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?

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 {}`.

<@U3ZLHBTLG> 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