UIViewController extension to instantiate view controller from storyboard or xib file of the same name

UIViewController.swift

import UIKit

extension UIViewController {

    static func initWithStoryboard(_ storyboard: UIStoryboard? = nil,
                                   _ identifier: String? = nil) -> UIViewController? {

        var _storyboard = storyboard

        if storyboard == nil {
            _storyboard = UIStoryboard(name: String(describing: self), bundle: nil)
        }

        guard _storyboard != nil else {
            return nil
        }

        if let identifier = identifier {
            return _storyboard?.instantiateViewController(withIdentifier: identifier)
        } else {
            return _storyboard?.instantiateInitialViewController()
        }
    }

    static func initWithNib() -> Self {
        return self.init(nibName: String(describing: self), bundle: nil)
    }

}