doesntWork.scala

import scalaz._
import argonaut._,Argonaut._                                                                                                                                                                                                                                                    

object JsonDb {

  sealed trait SumType
  case class Option1( foo:String ) extends SumType
  case class Option2( bar:Int    ) extends SumType

  private implicit val option1Codec = casecodec1( Option1.apply , Option1.unapply _ )("foo")
  private implicit val option2Codec = casecodec1( Option2.apply , Option2.unapply _ )("bar")

  def sumTypeCodecHelper2[A <: X,B <: X ,X](
    nameA:String , nameB:String
  )( implicit
    dA:DecodeJson[A], eA:EncodeJson[A], dB:DecodeJson[B], eB:EncodeJson[B]
  ) = CodecJson[X](
    (sumType) => Json.obj( sumType match {
      case o1:A => nameA := o1
      case o2:B => nameB := o2
    } ) ,
    c => ( (c --\ nameA).as[A] ||| (c --\ nameB).as[B] )
  )

  implicit def sumTypeCodec  = sumTypeCodecHelper2[Option1,Option2,SumType]("option1","option2")

}