would an interface with those 3 fields work for you?

menegatti: I was hoping of doing it in another way.

You could use delegation to do something like this:

interface A {
    val fieldA: String
    val fieldB: String
    val fieldC: String
}

data class FirstClass(
        override val fieldA: String, 
        override val fieldB: String, 
        override val fieldC: String) : A

data class SecondClass(val firstClass: FirstClass, val fieldD: String) : A by firstClass

The extra interface declaration is bugging me. if there was any other way..

there isn't any

If the classes are conceptually related, I think it really does make sense to extract that interface.

They are request-response for a particular web service, and i find it not suitable to extend an interface. Currently, I ended up copying the same fields to the other classes as well. the other class does have few extra fields as well.

then maybe they are related

I meant these two were the request and response for one webservice. the other requests and response don’t share the similar behaviour.

I see