Error in serializing classes with traits on Scala using pickling?

Question

I am trying to serialize a Scala class using Pickling.

  import scala.pickling.Defaults._
  import scala.pickling.json._

  trait Tr[T<: Tr[T]]{}
  class Sub(z: Int) extends Tr[Sub] {}
  class Data(b: Tr[_])

  val message = new Data(new Sub(1)).pickle.value

I am getting this error on compilation:

Error:..... type arguments [_$2] do not conform to trait Tr's type parameter bounds [T <: Tr[T]] val message = new Data(new Sub(1)).pickle.value

Answer 1

What about using the following class hierarchy:

trait Tr[T <: Tr[T]]
case class Sub(z: Int) extends Tr[Sub]
case class Data[T <: Tr[T]](b: T)

val message = Data(Sub(1)).pickle.value

that is pickled like:

{
  "$type": "Data[Sub]",
  "b": {
    "z": 1
  }
}