Swift: Follow Article "Swift: Failable Enums with Optionals" http://natashatherobot.com/swift-failable-enums-with-optionals/?utm_campaign=This_Week_in_Swift_14&utm_medium=email&utm_source=This%2BWeek%2Bin%2BSwift

ViewController.swift

extension String {
    func toEnum<Enum: RawRepresentable where Enum.RawValue == String>() -> Enum? {
        return Enum(rawValue: self)
    }
}


class ViewController: UIViewController {
                            
   .............
    
    //  Replace Magic Strings with Enumerations in Swift
    
    enum SegueIdentifier: String {
        case SegueToRedViewIdentifier = "SegueToRedViewIdentifier"
        case SegueToGreenViewIdentifier = "SegueToGreenViewIdentifier"
        case SegueToBlueViewIdentifier = "SegueToBlueViewIdentifier"
    }
    
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        let y: SegueIdentifier? = segue.identifier?.toEnum()           // IMPORTANT!
        if let segueIdentifier =  y {

            switch segueIdentifier {
            case .SegueToRedViewIdentifier:
                println("red")
            case .SegueToGreenViewIdentifier:
                println("green")
            case .SegueToBlueViewIdentifier:
                println("blue")
            }
        }
    }
    

}