WeakObserverExample.swift

import Foundation

protocol ExampleObserver:AnyObject {
	func methodThatDoesSomething()
}


class Example: NSObject {
	
	// MARK: - Observers
	
	/// Private helper class to maintain a weak reference to the observers
	fileprivate class WeakObserver {
		private(set) weak var value: ExampleObserver?
		
		init(value: ExampleObserver?) {
			self.value = value
		}
	}
	
	private var observers : [WeakObserver] = []
	
	func addObserver(_ observer: ExampleObserver) {
		self.observers = self.observers.filter({ $0.value != nil }) // Trim
		self.observers.append( WeakObserver(value: observer)  ) // Append
	}
	
	func removeObserver(_ observer: ExampleObserver) {
		self.observers = self.observers.filter({
			guard let value = $0.value else {
				return false
			}
			return !(value === observer)
		})
	}
	
	
	// MARK: - Usage
	
	func somethingHappened() {
		// .. do something ...
		
		// Update observers
		self.observers.forEach({ $0.value?.methodThatDoesSomething() })
	}
}