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var title: String
var titleLabel: UILabel

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var title: String {
        didSet {
            titleLabel.text = title
        }
    }

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let disposeBag = DisposeBag() 
let publishSubject = PublishSubject<String>()

//subscribe for changes
	publishSubject
	.subscribe(onNext: { title in
		titleLabel.text = title
	})
	.disposed(by: disposeBag)

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class ProfileManager {
     static let shared = ProfileManager()

     let usernameObservable: Observable<String>
     private let usernameSubject: BehaviorSubject<String>

     private var username: String {
        didSet {
            usernameSubject.onNext(username)
        }

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RAC(self, titleLabel.text) = RACObserve(self, title);

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@objc dynamic var titleKVO: String = ""
    var titleObserver: Observable<String> {
        return rx.observe(String.self, "titleKVO", options: .new) //using an Rx wrapper for KVO we can monitor new values of 
    }

    let disposeBag = DisposeBag()

	titleObserver            
	.subscribe(onNext: { title in
                titleLabel.text = title

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import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var loginTextField: UITextField?
    @IBOutlet weak var passwordTextField: UITextField?
    @IBOutlet weak var loginButton: UIButton?
    
    override func viewDidLoad() {
        super.viewDidLoad()

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 override func viewDidLoad() {
        super.viewDidLoad()
    
        loginButton?.isEnabled = false
        
        guard let loginTextField = loginTextField,
            let passwordTextField = passwordTextField,
            let loginButton = loginButton else {
                return
        }

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class ViewController: UIViewController {

    @IBOutlet weak var loginTextField: UITextField?
    @IBOutlet weak var passwordTextField: UITextField?
    @IBOutlet weak var loginButton: UIButton?
    
    private let disposeBag = DisposeBag()
    private let viewModel = ViewModel()
    
    override func viewDidLoad() {

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@Published var title: String = ""

//And then you can change the variable itself:
title = "Bob"

//And also to track its changes:
let titleSubscription = $title.sink {
    print("new title is '\($0)'")
}