(iOS) Swift only KVO alternative, event handlers

SwiftEventHandler.swift

//Documentation
//https://blog.scottlogic.com/2015/02/05/swift-events.html

//KVO example (not shown in this gist)
//https://blog.scottlogic.com/2015/02/11/swift-kvo-alternatives.html

public class Event<T> {

  public typealias EventHandler = T -> ()

  private var eventHandlers = [Invocable]()

  public func raise(data: T) {
  for handler in self.eventHandlers {
    handler.invoke(data)
    }
  }

  public func addHandler<U: AnyObject>(target: U,
            handler: (U) -> EventHandler) -> Disposable {
    let wrapper = EventHandlerWrapper(target: target,
                         handler: handler, event: self)
    eventHandlers.append(wrapper)
    return wrapper
  }
}

private protocol Invocable: class {
  func invoke(data: Any)
}

//----

public protocol Disposable {
  func dispose()
}

private class EventHandlerWrapper<T: AnyObject, U>
                                  : Invocable, Disposable {
  weak var target: T?
  let handler: T -> U -> ()
  let event: Event<U>

  init(target: T?, handler: T -> U -> (), event: Event<U>) {
    self.target = target
    self.handler = handler
    self.event = event;
  }

  func invoke(data: Any) -> () {
    if let t = target {
      handler(t)(data as U)
    }
  }

  func dispose() {
    event.eventHandlers =
       event.eventHandlers.filter { $0 !== self }
  }
}

//----

//Usage:

func someFunction() {

  // create an event
  let event = Event<(String, String)>()

  // add a handler
  let handler = event.addHandler(self, ViewController.handleEvent)

  // raise the event
  event.raise("Colin", "Eberhardt")

  // remove the handler
  handler.dispose()
}

func handleEvent(data: (String, String)) {
  println("Hello \(data.0), \(data.1)")
}