A Swift 2 error throwing example.

Example.swift

typealias CustomErrorType = protocol<ErrorType, CustomStringConvertible>

struct Example {
  
  enum Error: CustomErrorType {
    case ZombieApocalypse
    case RobotOverlords
    case Cthulhu
    
    var description: String {
      switch self {
        case ZombieApocalypse:
          return "Brains!!!!!!"
        case RobotOverlords:
          return "01110111 01100101 01101100 01100011 01101111 01101101 01100101"
        case Cthulhu:
          return "Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn"
      }
    }
  }
  
  func methodThatThrows() throws {
    // zombies!
    throw Error.ZombieApocalypse
    
    // robots!
    throw Error.RobotOverlords
    
    // lovecraft!
    throw Error.Cthulhu
  }
  
  func foo() {
    do {
      try methodThatThrows()
    } catch let error as Error {
      print(error)
      
      switch error {
        case .ZombieApocalypse:
          // handle a zombie apocalypse
        case .RobotOverlords:
          // handle robot overlords
        case .Cthulhu:
          // handle cthulhu (as if)
      }
    } catch {
      // Unexpected error
    }
  }
  
}