Is there a way to ensure a generic type is a data class?

Why would you want that?

I was trying to create a copy of a generic value which was only meant to be a data class

only meant to be a data class

Why? what's significant about a data class? Ultimately they're just normal classes with some functions generated for you, and even those functions can be overridden, so being a data class doesn't really get you anything.

I suppose. I guess I was trying to clone a generic type, and know that data classes have the

copy

method.

You could always make a

interface Copy<T> { fun copy(): T }

. Not sure how nicely it'll play with data classes though.

@Danilo Herrera Data classes can't do that, as their generated

copy

functions all have different signatures (unfortunately Kotlin doesn't consider a function with all default parameters the same as a function with no parameters), so even though you can cal

copy()

on all of them, they get compiled down to different (unrelated) function calls.

Problem with the

interface Copy

, the

copy

function of a data class has an unknown signature, except for its name and return type

I see. That makes sense. Ended up using this interface:

interface Cloneable<T> {
    fun clone(): T
}

which in turn makes the data classes have this implementation:

data class User(val id: String) : Cloneable<User> {
    fun clone() = copy()
}

You can get a bit more type safety with

interface Cloneable<T: Clonable<T>>