The ever-important Result type (without methods)

result.swift

enum Result<A> {
  case Success(Box<A>)
  case Failure(NSError)
}

// Due to current swift limitations, we have to include this Box in Result.
// Swift cannot handle an enum with multiple associated data (A, NSError) where one is of unknown size (A)
final class Box<T> {
  let unbox: T
  init(_ value: T) { self.unbox = value }
}

extension Result: Printable {
  var description: String {
    switch self {
    case Success(let box): return "Success: \(box.unbox)"
    case Failure(let err): return "Failure: \(err.description)"
      }
  }
}