UIViewController+Extensions.swift

// That’s marked @nonobjc so it won’t conflict with any of Apple’s own code, now or in the future.
@nonobjc extension UIViewController {
   func add(_ child: UIViewController, frame: CGRect? = nil) {
      addChildViewController(child)
      if let frame = frame {
         child.view.frame = frame
}
      view.addSubview(child.view)
      child.didMove(toParentViewController: self)
   }
   func remove() {
       guard parent != nil else {
            return
        }
      willMove(toParentViewController: nil)
      view.removeFromSuperview()
      removeFromParentViewController()

 } }


 //usage:

 guard let vc = storyboard?.instantiateViewController(withIdentifier: "Second") else { return }
 add(vc)
 performSlowWork(with: data) {
   vc.remove()
}