Pickling an abstract type

[julienrf]

Consider the following trait:

trait Module {

  type User <: UserLike

  trait UserLike {
    def name: String
  }

}

I’d like to write a function that pickles a value of type User, which is abstract. Here is what I came out with:

trait ModuleUsage extends Module {
  import scala.pickling._

  def pickle(u: User)(implicit p: SPickler[User], t: FastTypeTag[User]): Unit = {
    import binary._
    println(u.pickle)
  }

}

This trait can then be used as follows:

object ModuleUsageImpl extends ModuleUsage with App {

  // Implementation of the abstract type `User`
  case class User(name: String) extends UserLike

  // Why do I need these imports?
  import scala.pickling._
  import scala.pickling.binary._

  pickle(User("Heather"))

}

My problem is that I’d like to avoid the imports to at the ModuleUsageImpl site, especially the scala.pickling.binary._ import. By the way, if I import scala.pickling.json._ at this place, the pickling format is still binary (which is the one that is imported in the pickle function). Maybe my pickle function is not taking the right implicit parameters?

[julienrf]

If I trade the implicit parameters for implicit vals, the above code does not compile anymore:

trait ModuleUsage extends Module {
  import scala.pickling._

  implicit def p: SPickler[User]
  implicit def t: FastTypeTag[User]

  def pickle(u: User): Unit = {
    import binary._
    println(u.pickle)
  }

}

object ModuleUsageImpl extends ModuleUsage with App {

  case class User(name: String) extends UserLike

  import scala.pickling._
  import scala.pickling.binary._

  implicit val p = implicitly[SPickler[User]]
  implicit val t = implicitly[FastTypeTag[User]]

  pickle(User("Heather"))

}

I get the following error:

[info] pickling.this.SPickler.genPickler is not a valid implicit value for scala.pickling.SPickler[ModuleUsageImpl.User] because:
[info] stepping aside: repeating itself
[info]   implicit val p = implicitly[SPickler[User]]
[info]                              ^