[swift-users] Specifying A Dynamic Type In Swift Generics

Jon Akhtar jona at herbalife.com
Tue Jul 5 10:40:40 CDT 2016

I have a generic class that I would like to use. I¹ll include the whole

public final class EventRegistration<E: AppEvent> {
	private(set) var event: E?
	private var token: AnyObject?

	public init() {}

	public init(event: AppEvent, token: AnyObject) {
		self.event = event
		self.token = token

	public func unregister() {
		if let token = self.token,
	   	   let event = self.event {
		token = nil
		event = nil

	public var isRegistered: Bool {
		return token != nil

	deinit {

I would like to use this class in my AppEvent class. Among other things
AppEvent has a method register()

public class AppEvent : CustomStringConvertible {


	public func register(notification: (NSNotification! ->
Void))->EventRegistration<???> {
		let eventName = self.dynamicType.eventName()

		let token = 
NSNotificationCenter.defaultCenter().addObserverForName(eventName, object:
nil, queue: self.dynamicType.eventQueue(), usingBlock: notification)

		let registration = EventRegistration(event: self, token: token)

		return registration

I have 50-100 subclasses of AppEvent that I use directly.

public class SomeEvent: AppEvent {}
public class SomeOtherEvent: AppEvent {}
public class EvenSomeOtherEvent: AppEvent {}

They all inherit the register() function.

I would like the following.

Let some = SomeEvent().register() { note in }

some.event.self should be ³SomeEvent²

Because SomeEvent.register() returns EventRegistration<SomeEvent>

All the parts are there for this to be statically typed. If I implemented
register in each class I could get the behavior I want. What I am looking
for is a way to say ³the current dynamic type², sort of like ³Self².

Is there a signature for "public func register(notification:
(NSNotification! -> Void))->EventRegistration<???>" that would accomplish
this, or does this break some type rule I am not aware of, or is it just a
missing language feature.

If you want points, see:



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