typeclass.scala

def unWrapJson(json: JsonValue) =
    json match {
        case JsonString(value) => value
        case JsonDouble(value) => value.toString
    }

sealed trait JsonValue
case class JsonString(value: String) extends JsonValue
case class JsonDouble(value: Double) extends JsonValue

trait UnWrapJson[ +A ] {
    type Out
    def apply[A]( a: A ): Out
}

object UnWrapJson {
    implicit def unWrapJsonString: UnWrapJson[JsonValue] = new UnWrapJson [JsonValue] {
        type Out = String
        def apply[JsonString](json: JsonString) =
            json match {
                case JsonString(x) => x
            }
    }
}
def unWrap[T](json: T)(implicit unwrapjson: UnWrapJson[T]): unwrapjson.Out = unwrapjson(json)
val currentValue2: String = unWrap ( currentValue )