UIStoryboard.swift

extension UIStoryboard {
    enum Storyboard : String {
        case Main
        case News
        case Gallery
    }
    
    /**
     Better convenience initializer to hide ugly code
     
     - Usage: let storyboard = UIStoryboard(storyboard: .Main)
     */
    convenience init(storyboard: Storyboard, bundle: NSBundle? = nil) {
        self.init(name: storyboard.rawValue, bundle: bundle)
    }
    
    /**
     Convenience function that uses `StoryboardIdentifiable` (see below) to instantiate
     a specific type of view controller through UIStoryboard functions without typecasting.
     Helps avoid unsafe string literals too.
     
     - Usage: let viewController: MyViewController = storyboard.instantiateViewController()
     
     - Returns: Instance of UIViewController.
     */
    func instantiateViewController<T: UIViewController where T: StoryboardIdentifiable>() -> T {
        let optionalViewController = self.instantiateViewControllerWithIdentifier(T.storyboardIdentifier)
        
        guard let viewController = optionalViewController as? T  else {
            fatalError("Couldn’t instantiate view controller with identifier \(T.storyboardIdentifier) ")
        }
        
        return viewController
    }
}

/**
 Protocol which gives any class that conforms to it, a static variable, storyboardIdentifier. 
 Reduces the amount of work we have to do when managing identifiers for view controllers.
 Extend it only for UIViewController (or subclasses), so now we have a method to get the 
 storyboardIdentifier string dynamically from the class at runtime.
 */
protocol StoryboardIdentifiable {
    static var storyboardIdentifier: String { get }
}

extension StoryboardIdentifiable where Self: UIViewController {
    static var storyboardIdentifier: String {
        return String(self)
    }
}

extension UIViewController : StoryboardIdentifiable { }