Hello friendly Kotliners! I have an interface with a fun that returns some custom related datatype:

package somePkg

interface MyInterface {
  fun myFun(): MyType
  data class MyType
}

I don't want to pollute

somePkg

with

MyType

, since it's pretty specific to the domain of

MyInterface

, and there is other stuff in the same package. Are there any pitfalls to defining a data class inside an interface that I should be aware of? What about putting it inside companion object inside the interface? Is the only difference in the import statement you have to use?

For interfaces, yes. For classes, the nested class can access private members of it's containing class.

Really? I remember there being some difference between Java and Kotlin here, in that that wasn't allowed in Kotlin.

I also think

inner

keyword is required to access private members (ref. https://kotlinlang.org/docs/reference/nested-classes.html) However that's beside the question I'm asking 😛

Sorry, didn't spot the

private

part of your statement 🙂 You are right

Huh I remember being frustrated about something like this, dammit.

The reverse doesn't work though (outer access to private property of nested).

But this is still unrelated to whether defining data classes / types inside interface is reasonable or not, and whether they should exist directly in the interface, or within a companion object 😬

Personally I think it makes sense. Putting them in the companion object is a bit weird imho

That'st the plan, however i didn't want to clutter the "root" namespace

I think it makes perfect sense to put it in the interface if it will only be used through the interface.

👍