extension Array where Element: OptionalType {
  // Short hand for the original compactMap: we do not need to
  // pass in a selector function - instead just unwrap each
  // element in the Array to its base type.
  func compactMap() -> [Element.Wrapped] {
    return self.compactMap({$0.value})
  }
}

let a: [Int] = [0, 1, 2]
// a.compactMap() - compile error.
let b: [Int?] = [0, nil, 1, 2, nil]
let c: [Int] = b.compactMap()                  // Returns [1, 2, 3]