Observers swift

Observer.swift

import Foundation

public protocol Observable : class {
    typealias ObserverType
    func addObserver(observer : ObserverType)
    func removeObserver(observer : ObserverType)
}

let observersAssociatedKey = "observersKey"

extension Observable where Self: AnyObject, ObserverType : AnyObject {

    private var observers : NSHashTable  {
        get {
            if let observers = objc_getAssociatedObject(self, observersAssociatedKey) as? NSHashTable {
                return observers
            } else {
                let observers = NSHashTable.weakObjectsHashTable()
                objc_setAssociatedObject(self, observersAssociatedKey, observers, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
                return observers
            }
        }
    }

    public func addObserver(observer : ObserverType) {
        observers.addObject(observer)
    }

    public func removeObserver(observer : ObserverType) {
        observers.removeObject(observer)
    }

    public func notifyObservers(notify : (ObserverType) -> ()) {
        for observer in observers.allObjects {
            notify(observer as! ObserverType)
        }
    }
}

public protocol SubjectObserver : class {
    func subjectDidSomething()
}

public protocol Subject : Observable {
    typealias ObserverType = SubjectObserver
}

public class ConcreteSubject : Subject {
    public typealias ObserverType = ConcreteObserver // Otherwise doesn't compile, why? :(

    public func doSomething() {
        notifyObservers { (observer) -> () in
            observer.subjectDidSomething()
        }
    }
}

public class ConcreteObserver : SubjectObserver {
    public func subjectDidSomething() {

    }
}

Seems like compiler limitation. One solution:
https://gist.github.com/victorpimentel/1a963560d5183f887bca