Concise way to create day of week enumeration in Scala

Question

I'm new to Scala, so be nice please. You'll have to excuse me if I'm missing something obvious.

I'm trying to create an enum like structure to represent the days of the week in Scala. I want a method that accepts a string that can either be the numbers 1 through 7, the full name of the day, or a three letter abbreviation, with any capitalisation, and returns the correct day. Ideally I want to be able to retrieve the correct day simply by writing DayOfWeek(_), which as far as I understand things means this method needs to be apply. The individual values also have to be subclasses (or mix in) a trait called CalendarField, which at the moment defines no methods or members.

This is my current attempt:

object DayOfWeek extends Enumeration with CalendarField {

    val Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday = Value

    def apply(v:String) = {
        v.toUpperCase match {
            case Int(x) => x match {
                case 1 => Sunday
                case 2 => Monday
                case 3 => Tuesday
                case 4 => Wednesday
                case 5 => Thursday                  
                case 6 => Friday
                case 7 => Saturday
                case _ => throw new IllegalArgumentException("Invalid value for day of week: " + v)
            }
            case "SUN" | "SUNDAY" => Sunday
            case "MON" | "MONDAY" => Monday
            case "TUE" | "TUEDAY" => Tuesday
            case "WED" | "WEDNESDAY" => Wednesday
            case "THU" | "THURSDAY" => Thursday
            case "FRI" | "FRIDAY" => Friday
            case "SAT" | "SATURDAY" => Saturday
            case _ => throw new IllegalArgumentException("Invalid value for day of week: " + v)
        }
    }
}

object Int {
    def unapply(s : String) : Option[Int] = try {
        Some(s.toInt)
    } catch {
        case _ : java.lang.NumberFormatException => None
    }
}

This fails on a few points:

1. The individual values aren't subclasses of CalendarField - they are simply Values.
2. I've defined an apply method but DayOfWeek(_) doesn't work - my (vague) guess this is because it expects to call a constructor and DayOfWeek is an object, not a class? Or is it because Enumeration(s:String) is already used? Is there a way round this?

Any suggestions on how to get round these problems, or neater solutions, would be greatly appreciated. Thanks.

Answer 1

I'd probably implement something like this:

sealed trait DayOfWeek
case object Monday extends DayOfWeek
case object Tuesday extends DayOfWeek
// etc.

object DayOfWeek {
   def unapply(s: String): Option[DayOfWeek] = s.toUpperCase match {
      case Int(x) => x match {
         case 1 => Some(Sunday)
         // ...
         case _ => None
      }
      case "SUN" | "SUNDAY" => Some(Sunday)
      // ...
      case _ => None
   }

   def apply(s: String): DayOfWeek = s match {
      case DayOfWeek(d) => d
      case _ => throw new IllegalArgumentException(
                   "Invalid value for day of week: " + s)
   }

}