is there a way to create an extension function for an annotated data class?

Not really, neither "annotated" nor "data class" are represented by the type system.

yeah, data classes don’t inherit from anything but

Any

or implement any kind of interface by default, just like any other class

Theoretically you could generate them using an annotation processor

Thanks for the help. Is there a way to create an extension function on "Any" that has been annotated in some way?

you can annotate a lot of things, but based on this conversation I don’t think it’ll necessarily do what you want it to

Consider using an interface instead of an annotation.

Thanks. Maybe I should elaborate a bit more on my problem. So I am using kotlin's Json serializer to convert my data classes to a json string. I have code that looks like this sprinkled all throughout my code base (Json(JsonConfiguration.Stable).stringify(myType.serializer(), myType(a, b, c)) . I thought it would be nice to just create an extension function on my data class where I can do: myType(a,b,c).toJson()

Would you mind clarifying what you mean by “kotlin’s JSON serializer?”

hah, sure 🙂