notifiers.swift

import Foundation

@propertyWrapper struct Notifier<Value> {
  private let identifier: String

  var wrappedValue: Value? {
    didSet {
      NotificationCenter.default.post(name: Notification.Name(identifier), object: wrappedValue)
    }
  }

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

@propertyWrapper class Notified<Value> {
  private let identifier: String

  var wrappedValue: Value?

  init(identifier: String) {
    self.identifier = identifier

    NotificationCenter.default.addObserver(forName: Notification.Name(identifier), object: nil, queue: nil, using: {[weak self] notification in
      self?.wrappedValue = notification.object as? Value
    })
  }
}

struct Person {
  @Notifier(identifier: "person.name.changed")
  var name: String?

}

class Observer {
  @Notified(identifier: "person.name.changed")
  var name: String?
}

var person = Person()
var observer = Observer()

observer.name /// nil
person.name = "Hello world"
observer.name /// "Hello world"