A bit of a language question:

data class

can't be extended (ok). If I chose to use an

interface

and implement it with a

data class

I can do things like this

interface MyPublicInterface {
  val x: String
  val y: Int
  val z: Whatever
}

data class MyImplementation(
  override val x: String,
  override val y: Int,
  override val z: Whatever
): MyPublicInterface

now this is ok, but if I do this then I can't use the useful

copy()

or

componentN()

functions method that comes along with a data class on my interface without casting it to my implementation. Is there some way to make my interface declare the

copy()

and

componentN()

? for the

componentN()

I guess it's possible by just defining the operators, but then I'd had to manually maintain them, still ok. But for

copy()

I've no idea how to do it

What is your use case here? Why do you need interfaces for data classes?

Alas, there is no such way; there are no such things as `data interface`s....

yes that's the use case

data class Sub

being a subset of the data in

data class Over

sharing the same interface matching Sub. or, as an alternative

data class A

and

data class B

sharing a subset of data that could be represented by an interface. An API returning the interface. In theory you could use

copy()

limited to the attributes of the common set and still create a valid

A

or

B

class.