Hello friendly Kotliners! I have an interface with...

# announcements

[arve]

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?

[diesieben07]

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

[karelpeeters]

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

[karelpeeters]

inner classes can access private members though.

[arve]

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 😛

[diesieben07]

https://try.kotlinlang.org/#/UserProjects/qbaiujbvuiokdgs31dkhfcja1m/ud9s7d0efj8e2f6jlo5b8gm7gu

[arve]

Sorry, didn't spot the private part of your statement 🙂 You are right

[karelpeeters]

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

[diesieben07]

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

[arve]

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 😬

[diesieben07]

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

[diesieben07]

However if you simply don't want to clutter the file system, you can put multiple top level types in one .kt file, too.

[arve]

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

[aarjav]

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

[arve]

👍