Container View Controller in swift 4

import UIKit

class MasterViewController: UIViewController {
    
    @IBOutlet var segmentedControl: UISegmentedControl!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupView()
    }
    
}

private func setupView() {
    setupSegmentedControl()
}

private func setupSegmentedControl() {
    // Configure Segmented Control
    segmentedControl.removeAllSegments()
    segmentedControl.insertSegment(withTitle: "Summary", at: 0, animated: false)
    segmentedControl.insertSegment(withTitle: "Sessions", at: 1, animated: false)
    segmentedControl.addTarget(self, action: #selector(selectionDidChange(_:)), for: .valueChanged)
    
    // Select First Segment
    segmentedControl.selectedSegmentIndex = 0
}
func selectionDidChange(_ sender: UISegmentedControl) {
    updateView()
}
private lazy var summaryViewController: SummaryViewController = {
    // Load Storyboard
    let storyboard = UIStoryboard(name: "Main", bundle: Bundle.main)
    
    // Instantiate View Controller
    var viewController = storyboard.instantiateViewController(withIdentifier: "SummaryViewController") as! SummaryViewController
    
    // Add View Controller as Child View Controller
    self.add(asChildViewController: viewController)
    
    return viewController
}()

private lazy var sessionsViewController: SessionsViewController = {
    // Load Storyboard
    let storyboard = UIStoryboard(name: "Main", bundle: Bundle.main)
    
    // Instantiate View Controller
    var viewController = storyboard.instantiateViewController(withIdentifier: "SessionsViewController") as! SessionsViewController
    
    // Add View Controller as Child View Controller
    self.add(asChildViewController: viewController)
    
    return viewController
}()
private func add(asChildViewController viewController: UIViewController) {
    // Add Child View Controller
    addChildViewController(viewController)
    
    // Add Child View as Subview
    view.addSubview(viewController.view)
    
    // Configure Child View
    viewController.view.frame = view.bounds
    viewController.view.autoresizingMask = [.flexibleWidth, .flexibleHeight]
    
    // Notify Child View Controller
    viewController.didMove(toParentViewController: self)
}
private func updateView() {
    if segmentedControl.selectedSegmentIndex == 0 {
        remove(asChildViewController: sessionsViewController)
        add(asChildViewController: summaryViewController)
    } else {
        remove(asChildViewController: summaryViewController)
        add(asChildViewController: sessionsViewController)
    }
}
func setupView() {
    setupSegmentedControl()
    
    updateView()
}