Generic Observer Pattern in Swift using Protocols gives Segmentation Fault - swift

Question

import Foundation
class IProtocol {
func meth1(arg: Int){}
}
class IObserver: IProtocol {
private var className: String
init(name: String) {
className = name
}
override func meth1(arg: Int) {
print(className, ":", arg)
}
}
class Notifier<T> {
private var listOfObservers = NSMutableArray()
func addObserver(observer: T) {
listOfObservers.add(observer)
}
func callObservers<ARG, RET>(function: (T)->(ARG)->RET, arg: ARG) {
for obj in listOfObservers {
let observer = obj as! T
_ = function(observer)(arg)
}
}
}
let a = IObserver(name: "First I Observer")
let b = IObserver(name: "Second I Observer")
let n = Notifier<IProtocol>()
n.addObserver(observer: a)
n.addObserver(observer: b)
n.callObservers(function: IProtocol.meth1, arg: Int(1))
OUTPUT
First I Observer: 1
Second I Observer: 1
The above example fails and does not build giving Command failed due to signal: Segmentation Fault: 11, when I change IProtocol to protocol from class. I have different protocols and different observer classes confirming those protocols. I am trying to implement a Notifier class that notifies the observers by taking the method from the protocol and arguments to be passed for that method.It will be great, if someone can explain what am I doing wrong!
I am using Swift 3 and Xcode 8.2

Answer 1

As of today, Swift does not handle direct references to protocol methods:
protocol IProtocol {
func meth1()
}
class IObserver: IProtocol {
func meth1() { print("success") }
}
let x = IProtocol.meth1 // This causes the compiler crash
x(IObserver())()
And coming to the solution for my problem was to pass a closure instead of the method. This is how it looks:
import Foundation
protocol IProtocol {
func meth1(arg: Int)
}
class IObserver: IProtocol {
private var className: String
init(name: String) {
className = name
}
func meth1(arg: Int) {
print(className, ":", arg)
}
}
class Notifier<T> {
private var listOfObservers = NSMutableArray()
func addObserver(observer: T) {
listOfObservers.add(observer)
}
func callObservers<ARG>(function: (T, ARG) -> (), arg: ARG) {
for obj in listOfObservers {
let observer = obj as! T
function(observer, arg)
}
}
}
let a = IObserver(name: "First I Observer")
let b = IObserver(name: "Second I Observer")
let n = Notifier<IProtocol>()
n.addObserver(observer: a)
n.addObserver(observer: b)
n.callObservers(function: {obs, ar in
obs.meth1(arg: ar)
}, arg: Int(1))