FutureSwiftyResponderChain

/* This is an alternate responder chain implementation that
   DOES NOT work in Swift 2.2, but might in a
   hypothetical future version of Swift. */

protocol Command {
}

protocol ResponderChainable {
    var nextResponder: ResponderChainable? { get }
}

protocol Responder: ResponderChainable {
    associatedtype AssociatedCommand: Command
    func canPerformCommand(command: AssociatedCommand) -> Bool
    func performCommand(command: AssociatedCommand)
}

extension Responder {
    func canPerformCommand(command: Command) -> Bool {
        if let command = command as? AssociatedCommand {
            return self.canPerformCommand(command)
        }
        return false
    }
    func performCommand(command: Command) {
        if let command = command as? AssociatedCommand {
            self.performCommand(command)
        }
    }
}

class View {
    var superView: View? = nil
}

extension View: ResponderChainable {
    var nextResponder: ResponderChainable? { return self.superView }
}

/* Declare commands */

// Copy

struct CopyCommand: Command {
}

protocol CopyResponder: Responder {
    func canPerformCommand(command: CopyCommand) -> Bool
    func performCommand(command: CopyCommand)
}

// Go Fishing

struct GoFishingCommand: Command {
}

protocol GoFishingResponder: Responder {
    func canPerformCommand(command: GoFishingCommand) -> Bool
    func performCommand(command: GoFishingCommand)
}

// Declare ability to respond to commands

class MyView: View {
}

extension MyView: CopyResponder { // Error: Can't figure out conformance to Responder
    func canPerformCommand(command: CopyCommand) -> Bool {
        return true
    }
    func performCommand(command: CopyCommand) {
        print("MyView copy")
    }
}

extension MyView: GoFishingResponder {
    func canPerformCommand(command: GoFishingCommand) -> Bool {
        return true
    }
    func performCommand(command: GoFishingCommand) {
        print("MyView go fishing")
    }
}

let v: ResponderChainable = MyView()
v.canPerformCommand(CopyCommand()) // Error because v is not a Responder
(v as? Responder)?.canPerformCommand(CopyCommand()) // Error because can't cast to Responder