Case class with Enumeration is not converted

I’m trying to convert a case class that has a Enumeration as a argument

import io.circe._, io.circe.generic.auto._, io.circe.jawn._, io.circe.syntax._
object WeekDay extends Enumeration {
  val Mon, Tue, Wed, Thu, Fri, Sat, Sun = Value
}
case class test1(day: WeekDay.Value)
case class test2(day: String)

While test2(“Mon”).asJson works as expected:

{
  "day" : "Mon"
}

But: test1(WeekDay.Mon).asJson results in:

<console>:27: error: could not find implicit value for parameter encoder: io.circe.Encoder[test] test(WeekDay.Mon).asJson

Is there a way to work around this or is this a bug?

[dhensche]

I’m not seeing anywhere in the project where basic scala Enumerations have a provided Encoder/Decoder instance. However, following how the json4s handled this I came up with the following

class EnumTranscoder[E <: Enumeration](enum: E) extends Decoder[E#Value] with Encoder[E#Value] {
  override def apply(c: HCursor): Result[E#Value] = Decoder.decodeString.map(enum.withName).apply(c)

  override def apply(a: E#Value): Json = Encoder.encodeString.apply(a.toString)
}

[travisbrown]

Yes, we’d want them to be in the companion objects so that they get made available without additional imports. Thanks, @mariussoutier!