title: enum conformance to RawRepresentable
body: <p>In the Swift book, the example for enums works fine </p>
  
  <pre><code>enum CompassPoint: String {
      case north, south, east, west
  }
  
  var northCom = CompassPoint.north
  print (northCom)
  </code></pre>
  
  <p>However I want to use a failable initializer so made an example of this</p>
  
  <pre><code>enum WeekDay: String {
      case monday, tuesday, wednesday, thursday, friday
      init?(rawValue: Int){
          switch rawValue {
          case 0 : self = .monday
          case 1 : self = .tuesday
          case 2 : self = .wednesday
          case 3 : self = .thursday
          case 4 : self = .friday
          default : return nil
          }
      }
  }
  </code></pre>
  
  <p>And get an error that Weekday does not conform to RawRepresentable - although I feel that conformance should be synthesized by the compiler so do not understand why this does not compile.</p>
  
  <p><strong>What I've done</strong> Created a similar working example (to see what the issue is), and still I want to conform to RawRepresentable using an enum with a failable initializer. I cannot find an example of this in the Swift book, in Stack Overflow questions or on the wider internet.</p>
  
  <p><strong>What I've provided</strong> Given a full example above, with the error as well as a working example of the behaviour I'm expecting.</p>
  
  <p><strong>What is not helpful</strong> Referencing the Swift book through a link or a comment is not helpful, as I've taken an example from there. I want to build on that example with a failable initializer. It is also not helpful to NOT use a enum, or a failable initializer. The question is about using a failable initalizer with a enum, and conforming to RawRepresentable. This is not homework, but those are the constraints of the question for my own learning and I'm interested in the outcome.</p>
  
  <p><strong>The question</strong> How can I use a failable initializer, with an enum as in the non-working example?</p>