natebirkholz

let tapClosure: (UITapGestureRecognizer) -> () = { (tapRecognizer) in
     print("In tap closure") 
} 
let recognizer = ClosureGestureRecognizer(action: tapClosure)

natebirkholz

class ClosureGestureRecognizer<GestureRecognizer: UIGestureRecognizer> {
    fileprivate var recognizer: GestureRecognizer
    private var actionHandler: ((GestureRecognizer) -> Void)

    init(action: @escaping (GestureRecognizer) -> ()) {
        self.recognizer = GestureRecognizer()
        self.actionHandler = action
        self.recognizer.addTarget(self, action: #selector(handleAction))
    }

natebirkholz

let closure: () -> () = {
    print("In Closure!")
}

let button = ClosureButton(frame: CGRect(x: 10, y: 10, width: 100, height: 20))
button.setTitle("Closure", for: .normal)
button.sizeToFit()
button.addClosureForEvent(.touchUpInside, closure: closure)

natebirkholz

class ClosureButton: UIButton {
    private var actionHandler: (() -> ())?

    func addClosureForEvent(_ event: UIControlEvents, closure: @escaping () ->()) {
        self.addTarget(self, action: #selector(handleAction), for: event)
    }

    @objc private func handleAction() {
        actionHandler?()
    }

natebirkholz

class HelloViewController: UIViewController {
  let label = UILabel(frame: .zero)
    
  override func viewDidLoad() {
    super.viewDidLoad()
    label.text = "Hello world!"
    label.translatesAutoresizingMaskIntoConstraints = false
    label.font = UIFont.systemFont(ofSize: 16.0, weight: .medium)
    label.textColor = .black
    label.textAlignment = .center

natebirkholz

let attributes = [ NSForegroundColorAttributeName : self.view.tintColor ]
let attributedString = NSAttributedString(string: NSLocalizedString("Sign In", comment: ""), attributes: attributes)
warns: (Expression implicitly coerced from 'UIColor?' to Any)

right way:
let attributes: [ String : UIColor ]
if let maybeAttributes = [ NSForegroundColorAttributeName : self.view.tintColor ] {
  attributes = maybeAttributes
} else {
  assertionFailure("self.view.tintColor is nil")

natebirkholz

class SuperClass {
    
    var aBool : Bool = false {
        didSet {
            print(aBool)
        }
    }
    
}