Custom Scala enum, most elegant version searched

Question

For a project of mine I have implemented a Enum based upon

trait Enum[A] {
  trait Value { self: A =>
    _values :+= this
  }
  private var _values = Li         


        

Answer 1

The article "“You don’t need a macro” Except when you do" by Max Afonov maxaf describes a nice way to use macro for defining enums.

The end-result of that implementation is visible in github.com/maxaf/numerato

Simply create a plain class, annotate it with @enum, and use the familiar val ... = Value declaration to define a few enum values.

The @enum annotation invokes a macro, which will:

• Replace your Status class with a sealed Status class suitable for acting as a base type for enum values. Specifically, it'll grow a (val index: Int, val name: String) constructor. These parameters will be supplied by the macro, so you don't have to worry about it.
• Generate a Status companion object, which will contain most of the pieces that now make Status an enumeration. This includes a values: List[Status], plus lookup methods.

Give the above Status enum, here's what the generated code looks like:

scala> @enum(debug = true) class Status {
     |   val Enabled, Disabled = Value
     | }
{
  sealed abstract class Status(val index: Int, val name: String)(implicit sealant: Status.Sealant);
  object Status {
    @scala.annotation.implicitNotFound(msg = "Enum types annotated with ".+("@enum can not be extended directly. To add another value to the enum, ").+("please adjust your `def ... = Value` declaration.")) sealed abstract protected class Sealant;
    implicit protected object Sealant extends Sealant;
    case object Enabled extends Status(0, "Enabled") with scala.Product with scala.Serializable;
    case object Disabled extends Status(1, "Disabled") with scala.Product with scala.Serializable;
    val values: List[Status] = List(Enabled, Disabled);
    val fromIndex: _root_.scala.Function1[Int, Status] = Map(Enabled.index.->(Enabled), Disabled.index.->(Disabled));
    val fromName: _root_.scala.Function1[String, Status] = Map(Enabled.name.->(Enabled), Disabled.name.->(Disabled));
    def switch[A](pf: PartialFunction[Status, A]): _root_.scala.Function1[Status, A] = macro numerato.SwitchMacros.switch_impl[Status, A]
  };
  ()
}
defined class Status
defined object Status