JSON4S type hint does not work

Implement Contact using traits and it will work.

This is an example of how you could use FullTypeHints.

You cannot ask implicitly for a Validable[Field], neither adding multiple explicit arguments lists (and this happens also for implicitly parameters, see note below) because they are not supported by JSON4S.

Note: asking for a Validable[Field] implicitly with Contact[Field: Validable] syntax is equal to adding an additional arguments list with implicit validable: Validable[Field].

You could, instead, add an additional parameter validable: Validable[Field] to the Contact constructor or (as in the example below) a validable field that should be overridden by concrete classes (like Mail) extending the Contact abstract class.

trait Validable[T]{  def valid(field: T): Boolean}abstract class Contact[Field](  val field: Field, val created: Long,   val updated: Long, val note: String) {  val validable: Validable[Field]}object Contacts{ val classList = List(classOf[Mail]) }case class Mail(  override val field: String,  override val created: Long = System.currentTimeMillis(),  override val updated: Long = System.currentTimeMillis(),  override val note: String) extends Contact[String](field, created, updated, note){  override val validable: Validable[String] = Mail}case object Mail extends Validable[String] {  override def valid(field: String): Boolean = true}implicit val formats = DefaultFormats + FullTypeHints(Contacts.classList)

val mail: List[Mail] = List(Mail(field = "random@mail.com", note = "Random note."))val serialized = Serialization.write(mail)val mailS = Serialization.read[List[Contact[_]]](serialized)print(mail == mailS)

The serialized JSON representation is the following:

[  {    "jsonClass":"whatever.core.entities.utility.contact$Mail",    "field":"random@mail.com",    "created":1509098018776,    "updated":1509098018776,    "note":"Random note."  }]