Observable.swift

Observable.swift

class Observable<T> {
  
  var value: T? {
    didSet {
      listener?(value)
    }
  }
  
  private var listener: ((T?) -> Void)?
  
  init(_ value: T?) {
    self.value = value
  }
  
  bind(_ listener: @escaping (T?) -> Void) {
    self.listener = listener
  }
}

Observable2.swift

public final class Observable<Value> {
    
    struct Observable<Value> {
        weak var observer: AnyObject?
        let block: (Value) -> Void
    }
    
    private var observers = [Observable<Value>]()
    
    public var value: Value {
        didSet { notifyObservers() }
    }
    
    public init(_ value: Value) {
        self.value = value
    }
    
    public func observe(on observer: AnyObject, observerBlock: @escaping (Value) -> Void) {
        observers.append(Observable(observer: observer, block: observerBlock))
        observerBlock(self.value)
    }
    
    public func remove(observer: AnyObject) {
        observers = observers.filter { $0.observer !== observer }
    }
    
    private func notifyObservers() {
        for observer in observers {
            DispatchQueue.main.async { observer.block(self.value) }
        }
    }
}