Json4s alternative api with scala generics / type members

Question

I know there is an xpath like api to get fields out of a JObject in Json4s

val x = (obj \ "Type").asInstanceOf[JString].values

However it feels a bit cumbersome and I'm not a fan of symbolic like apis. I kind of want something like this:

implicit class JsonExtensions(json: JObject) {

  def get[T <: JValue](key: String) : T.Values = {
     (json \ key).asInstanceOf[T].values
  }
}

and use it something like this

val x  = obj.get[String]("type")

However it doesn't compile, T's upper bound is a JValue so Id expect to be able to reference the type member Values which is on all JValues. For reference his is a snipper of JValue:

sealed abstract class JValue extends Diff.Diffable with Product with Serializable {
    type Values
    def values: Values
...
}

I'm new to scala, how can i make the compiler happy?

Answer 1

Here is the solution if anyone is interested:

implicit class JsonExtensions(json: JValue) {

  def get[T <: JValue](key: String) : T#Values = {
    (json \ key).asInstanceOf[T].values
  }
}

val x = obj.get[JString]("type")

You have to specify the expected type but x will the underlying Values of the Json Ast type. So for JString is a string, for JObject its a Map[String,Any]

Thank you insan-e