class ViewController : UIViewController {

    //MARK: - outlets
    @IBOutlet weak var firstView: FirstUiview!

}

class FirstUiview : UIView {

        //creating an instance of secondUiView
        lazy var mySecondView: SecondViewClass = {
          let dv = SecondViewClass()
          dv.backgroundColor = UIColor.red
          return dv
        }()


        //sometime later by clicking on a button
        self.addSubview(mySecondView)

        //a button will be tapped to remove mySecondView;
        //later will be called at some point upon tapping:

       func removingSecondViewByTapping()  {
         if mySecondView.isDescendant(of: self) {
           mySecondView.removeFromSuperview()
        }
       }

}

class SecondViewClass : UIView {

      //in this class I create bunch of uiview objects like below:
      lazy var aView : UIView = {
        let hl = UIView()
        hl.tag = 0
        hl.backgroundColor = UIColor.lightGray
        return hl
      }()

      self.addSubview(aView) //... this goes on and I add other similar views the same way.

        //creating an instance of thirdView
        var let thirdView = UIView()
        self.addSubview(thirdView)

}

class FirstView: UIView {

    weak var secondView: SecondView?       // note the `weak` reference, which is obviously an optional

    //sometime later by clicking on a button

    func doSomething() {
        let subview = SecondView()
        subview.backgroundColor = .red
        self.addSubview(subview)
        secondView = subview
    }

    // a button will be tapped to remove secondView;
    // later will be called at some point upon tapping ...

    func removingSecondViewByTapping()  {
        secondView?.removeFromSuperview()
    }
}