Partial instantiation is cool and all, but tbh I prefer just capturing the initial incomplete attributes in one complete record, pass that around, and then instantiate the real thing when you have all attributes

    data class IncompletePerson(val name: String)

    data class Person(
      val name: String, 
      val email: String
    )

or

    data class Person(
      val initialAttributes: IncompletePerson, 
      val email: String
    )

if you want to nest it.

if you're the type to instead do this

    data class Person(
      val name: String, 
      val email: String?
    )

I never want to work with your code. Now, there's no disambiguation between the complete object and the incomplete one, I always have to check before doing anything with it, and people will inevitably try send an incomplete object someplace that can't handle it and generate bugs.