Extension: Add and remove child view controller

childViewController.swift

    /// Add a child view controller
    ///
    /// - Parameter child: The child view controller
    func add(_ child: UIViewController) {
        addChildViewController(child)
        view.addSubview(child.view)
        child.didMove(toParentViewController: self)
    }


    /// Remove the view controller from the parent
    func remove() {
        guard parent != nil else {
            return
        }

        willMove(toParentViewController: nil)
        removeFromParentViewController()
        view.removeFromSuperview()
    }