add a built-in ArgBuilder for enums

[dontgitit]

I didn't make it implicit like all the other ArgBuilders because its type conflicts with the existing ArgBuilder[String]

[dontgitit]

can also potentially provide something like this for Java enums:

  implicit def enumArgBuilder[T <: java.lang.Enum[T]: ClassTag]: ArgBuilder[T] =
    enum.map(v => java.lang.Enum.valueOf[T](summon[ClassTag[T]].runtimeClass.asInstanceOf[Class[T]], v))

not entirely sure how to do that for Scala enums since scala.reflect.Enum doesn't provide valueOf (but I think actual subclasses do?)

[dontgitit]

or maybe something like this:

implicit def enumArgBuilder[T <: java.lang.Enum[T]: ClassTag]: ArgBuilder[T] =
  `enum`.flatMap { value =>
    val cls = summon[ClassTag[T]].runtimeClass.asInstanceOf[Class[T]]
    Try {
      java.lang.Enum.valueOf[T](cls, value)
    }.toEither.left.map { t =>
      ExecutionError(s"'$value' is not a valid value of ${cls.getSimpleName}", innerThrowable = Some(t))
    }
  }

[ghostdogpr]

Is the goal to use this + map for enums?

[dontgitit]

that's correct, that was the intention!

i guess maybe to make that clearer, it should be something like the following...?

private lazy val enumBuilder: ArgBuilder[String]                  = {
   case EnumValue(value) => Right(value)
   case other            => Left(InvalidInputArgument("Enum", other))
}

def `enum`[A](f: T => A): ArgBuilder[A] = enumBuilder.map(f)

def `enum`[A](f: T => Either[ExecutionError, A]): ArgBuilder[A] = enumBuilder.flatMap(f)

[ghostdogpr]

That would be f: String => ..., right? Maybe we can call it enumString and drop the backticks.