Responder chain in Swift using enums

responder-chain.swift

//: Responder chain in Swift using enums

protocol CommandProtocol {}

protocol Responder: class {
	var nextResponder: Responder? { get }
	
	func performerForCommand
		<Command : CommandProtocol>
		(command: Command) -> (() -> ())?
	
	func noResponderForCommand
		<Command : CommandProtocol>
		(command: Command)
	
	func performCommand
		<Command : CommandProtocol>
		(command: Command) -> Bool
}

extension Responder {
	func noResponderForCommand
		<Command : CommandProtocol>
		(command: Command) {
		print("Beep")
	}
	
	func performCommand
		<Command : CommandProtocol>
		(command: Command) -> Bool {
		if let performer = performerForCommand(command) {
			performer()
			return true
		}
		else {
			noResponderForCommand(command)
			return false
		}
	}
}

enum PasteboardCommand : CommandProtocol {
	case copy
	case cut
}

enum WindowCommand : CommandProtocol {
	case minimize
	case close
}


class View : Responder {
	weak var nextResponder: Responder?
	
	func performerForCommand
		<Command : CommandProtocol>
		(command: Command) -> (() -> ())? {
		return nextResponder?.performerForCommand(command)
	}
}

class MyView : View {
	override func performerForCommand
		<Command : CommandProtocol>
		(command: Command) -> (() -> ())? {
		if let command = command as? PasteboardCommand {
			switch command {
			case .copy: return copy
			case .cut: return cut
			}
		}
		
		return super.performerForCommand(command)
	}
	
	func copy() {
		print("Copy")
	}
	
	func cut() {
		print("Cut")
	}
}

class Window : Responder {
	weak var nextResponder: Responder?
	
	var contentView: View? {
		didSet {
			contentView?.nextResponder = self
		}
	}
	
	func performerForCommand
		<Command : CommandProtocol>
		(command: Command) -> (() -> ())? {
		if let command = command as? WindowCommand {
			switch command {
			case .minimize: return minimize
			case .close: return close
			}
		}
		
		return nextResponder?.performerForCommand(command)
	}
	
	func minimize() {
		print("Minimize")
	}
	
	func close() {
		print("Close")
	}
}


var view = MyView()
var window = Window()
window.contentView = view


let copyResponder = view.performerForCommand(PasteboardCommand.copy)
let respondsToCopy = copyResponder != nil

// view copy
view.performCommand(PasteboardCommand.copy) // true
// view minimize
view.performCommand(WindowCommand.minimize) // true
// window cut
window.performCommand(PasteboardCommand.cut) // false
// window close
window.performCommand(WindowCommand.close) // true