lost type relationships - with Self

Ordered-withSelf.swift

/** 
* Example from: Protocol-oriented Programming in Swift - WWDC 2015 
* https://developer.apple.com/videos/play/wwdc2015/408/
*/
protocol Ordered {
  func precedes(other: Self) -> Bool
}

// value type struct
struct Number: Ordered {
  var value: Double = 0
  // we can now use Number: no more lost type
  override func precedes(other: Number) -> Bool {
    return self.value < other.value
  }
}