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

[Jon Akhtar]

Yes, that is what I thought too. But when I try to do it, I get this error:

Error:(57, 23) 'Self' is only available in a protocol or as the result of
a method in a class; did you mean 'AppEvent’?

Thanks,

Jon



On 7/5/16, 12:15, "swift-users-bounces at swift.org on behalf of Kenny Leung
via swift-users" <swift-users-bounces at swift.org on behalf of
swift-users at swift.org> wrote:

>So, restating the question:
>
>You want to have a method on a class such that it will return an object
>which is genericised with that class. Like:
>
>class A {
>    func createB() -> B<Self> {
>    }
>}
>
>So that if you have C which is a subclass of A, calling createB() would
>return B<C>, and not B<A>
>
>Is that correct?
>
>-Kenny
>
>
>> On Jul 5, 2016, at 8:40 AM, Jon Akhtar via swift-users
>><swift-users at swift.org> wrote:
>> 
>> I have a generic class that I would like to use. I¹ll include the whole
>> source.
>> 
>> 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 {
>> 			event.unregister(token)
>> 		}
>> 		token = nil
>> 		event = nil
>> 	}
>> 
>> 	public var isRegistered: Bool {
>> 		return token != nil
>> 	}
>> 
>> 	deinit {
>> 		unregister()
>> 	}
>> }
>> 
>> 
>> 
>> I would like to use this class in my AppEvent class. Among other things
>> AppEvent has a method register()
>> 
>> public class AppEvent : CustomStringConvertible {
>> 
>> 
>> Š
>> 
>> 	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:
>> 
>>http://stackoverflow.com/questions/38193012/specifying-a-dynamic-type-in-
>>sw
>> ift-generics
>> 
>> Thanks,
>> 
>> Jon
>> 
>> 
>> 
>> 
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>
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