NotificationManager.swift

import Foundation

class NotificationManager
{
  static let sharedManager = NotificationManager()
  var observersMap = [String:NSHashTable]()

  func add<T>(type: T.Type, observer: T) {
    let typeString = "\(T.self)"
    let observers: NSHashTable

    // get the weak set of observers matching this type
    if let set = observersMap[typeString] {
      observers = set
    } else {
      observers = NSHashTable.weakObjectsHashTable()
      observersMap[typeString] = observers
    }

    observers.addObject(observer as? AnyObject)
  }

  func make<T>(type: T.Type, @noescape closure: T -> Void) {
    let typeString = "\(T.self)"
    if let set = observersMap[typeString] {
      for observer in set.allObjects {
        closure(observer as! T)
      }
    }
  }
}

protocol TestProtocol {
  func hello()
}

class TestClass: TestProtocol {
  let name: String

  init(name: String) {
    self.name = name
  }

  func hello() {
    print("hello \(name)")
  }
}

let object = TestClass(name: "First")
let object2 = TestClass(name: "Second")

NotificationManager.sharedManager.add(TestProtocol.self, observer: object)
NotificationManager.sharedManager.add(TestProtocol.self, observer: object2)

NotificationManager.sharedManager.make(TestProtocol.self) { (item) -> Void in
  item.hello()
}