What is Scala 3 equivalent to this Scala 2 code that uses Enumeration and play-json?

Question

I have some code that works in Scala 2.{10,11,12,13} that I'm now trying to convert to Scala 3. Scala 3 does Enumeration differently than Scala 2. I'm trying to figure out how to convert the following code that interacts with play-json so that it will work with Scala 3. Any tips or pointers to code from projects that have already crossed this bridge?

// Scala 2.x style code in EnumUtils.scala 
import play.api.libs.json._
import scala.language.implicitConversions

// see: http://perevillega.com/enums-to-json-in-scala
object EnumUtils {
  def enumReads[E <: Enumeration](enum: E): Reads[E#Value] =
    new Reads[E#Value] {
      def reads(json: JsValue): JsResult[E#Value] = json match {
        case JsString(s) => {
          try {
            JsSuccess(enum.withName(s))
          } catch {
            case _: NoSuchElementException =>
              JsError(s"Enumeration expected of type: '${enum.getClass}', but it does not appear to contain the value: '$s'")
          }
        }
        case _ => JsError("String value expected")
      }
    }
  implicit def enumWrites[E <: Enumeration]: Writes[E#Value] = new Writes[E#Value] {
    def writes(v: E#Value): JsValue = JsString(v.toString)
  }
  implicit def enumFormat[E <: Enumeration](enum: E): Format[E#Value] = {
    Format(EnumUtils.enumReads(enum), EnumUtils.enumWrites)
  }
}
// ----------------------------------------------------------------------------------
// Scala 2.x style code in Xyz.scala
import play.api.libs.json.{Reads, Writes}

object Xyz extends Enumeration {
  type Xyz = Value
  val name, link, unknown = Value
  implicit val enumReads: Reads[Xyz] = EnumUtils.enumReads(Xyz)
  implicit def enumWrites: Writes[Xyz] = EnumUtils.enumWrites
}

@AndriyPlokhotnyuk Thank you, I'll look into that. – gknauth Mar 16 '22 at 11:39 — gknauth, Mar 16 '22 at 11:39
Note that this is self-promotion by @AndriyPlokhotnyuk – Tim Mar 16 '22 at 11:43 — Tim, Mar 16 '22 at 11:43
@Tim Roger. Happy to check out a community member's work. – gknauth Mar 16 '22 at 11:58 — gknauth, Mar 16 '22 at 11:58

Andriy Plokhotnyuk · Answer 1 · 2022-03-16T16:59:09.233

As an option you can switch to jsoniter-scala.

It supports enums for Scala 2 and Scala 3 out of the box.

Also it has handy derivation of safe and efficient JSON codecs.

Just need to add required libraries to your dependencies:

libraryDependencies ++= Seq(
  // Use the %%% operator instead of %% for Scala.js and Scala Native 
  "com.github.plokhotnyuk.jsoniter-scala" %% "jsoniter-scala-core"   % "2.13.5",
  // Use the "provided" scope instead when the "compile-internal" scope is not supported  
  "com.github.plokhotnyuk.jsoniter-scala" %% "jsoniter-scala-macros" % "2.13.5" % "compile-internal"
)

And then derive a codec and use it:

import com.github.plokhotnyuk.jsoniter_scala.core._
import com.github.plokhotnyuk.jsoniter_scala.macros._

implicit val codec: JsonValueCodec[Xyz.Xyz] = JsonCodecMaker.make

println(readFromString[Xyz.Xyz]("\"name\""))

BTW, you can run the full code on Scastie: https://scastie.scala-lang.org/Evj718q6TcCZow9lRhKaPw

What is Scala 3 equivalent to this Scala 2 code that uses Enumeration and play-json?

1 Answers1