I have imported my latest event publishing code into the Word Counter. Since the DomainEventType enum didn’t provide much value besides obtaining a notification name, I decided to get rid of it and obtain a name by another means.

In the current iteration (see the Gist), the event protocol reveals a static eventName. I also removed the duplicated notification factory from concrete events:

import Foundation

public typealias UserInfo = [NSObject : AnyObject]

public protocol DomainEvent {
    class var eventName: String { get }

    init(userInfo: UserInfo)
    func userInfo() -> UserInfo
}

public func notification<T: DomainEvent>(event: T) -> NSNotification {
    return NSNotification(name: T.eventName, object: nil, userInfo: event.userInfo())
}

It’s weird that I have to write notification<T: DomainEvent>(event: T) to access static properties of the event type. notification(event: DomainEvent) doesn’t work as of Swift 1.1., because “Accessing members of protocol type value ‘DomainEvent.Type’ is unimplemented”.

In a similar vein, a method like this doesn’t satisfy the generics requirement:

func foo(event: DomainEvent) {
    let notification = notification(event)
    // ...
}

But this does:

func foo<T: DomainEvent>(event: T) {
    let notification = notification(event)
    // ...
}

Mixing protocols and generics makes me wonder where the problem lies, but hey, it does work this way, although generics pose a slight performance penalty to protocols if I remember the WWDC talks correctly.