Circe and Scala's Enumeration type

Question

I\'m trying to wrap my head around Circe.

So, here\'s the model I\'ve been given:

object Gender extends Enumeration {
     type Gender = Value
     val M         


        

Answer 1

Try defining your own encoders and decoders for the enum using:

Decoder.enumDecoder[E <: Enumeration](enum: E)
Encoder.enumEncoder[E <: Enumeration](enum: E)

something like:

object JsonProtocol {
  implicit val genderDecoder: Decoder[Gender.Value] = Decoder.enumDecoder(Gender)
  implicit val genderEncoder: Encoder[Gender.Value] = Encoder.enumEncoder(Gender)
  implicit val productDecoder: Decoder[Product] = deriveDecoder
  implicit val productEncoder: Encoder[Product] = deriveEncoder
}

These are needed because the automatic/semiautomatic derivers only work for hierarchies of sealed traits and case classes as far as I know. The reason you see that error is because the derived codecs for Product will implicitly require encoders/decoders for the types of each of it's parameters. An encoder/decoder for String is a standard part of Circe, but you'll probably need to create ones for your own enumerations.

Answer 2

Have a look at enumeratum if you want to use enumerations with circe. You could then try something like this:

import enumeratum._

sealed trait Gender extends EnumEntry

case object Gender extends CirceEnum[Gender] with Enum[Gender] {

  case object Male extends Gender
  case object Female extends Gender
  case object Unisex extends Gender
  case object Unknown extends Gender

  val values = findValues
}

Gender.values.foreach { gender =>
    assert(gender.asJson == Json.fromString(gender.entryName))
}

This should work with circe's automatic derivation for use with your case classes.