instantiateVC.swift

enum AppStoryboard: String {
    case main = "Main"
}

extension UIViewController {
    static func instantiate<T: UIViewController>(by storyboardName: AppStoryboard) -> T? {
        let type = String(describing: T.Type.self)
        guard let identifier = type.components(separatedBy: ".").first else { return nil }
        let storyboard = UIStoryboard(name: storyboardName.rawValue, bundle: nil)
        let vc = storyboard.instantiateViewController(withIdentifier: identifier)
        
        return vc as? T
    }
}

///Example
class MyViewController: UIViewController {
    
    lazy var otherVC: OtherViewController? = UIViewController.instantiateVC(by: .main)
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        if let vc =  otherVC {
            present(vc, animated: true)
        }
    }
}


///If always use in the view controller
extension UIViewController {
    func instantiate<T: UIViewController>(by storyboardName: AppStoryboard) -> T? {
        let type = String(describing: T.Type.self)
        guard let identifier = type.components(separatedBy: ".").first else { return nil }
        let storyboard = UIStoryboard(name: storyboardName.rawValue, bundle: nil)
        let vc = storyboard.instantiateViewController(withIdentifier: identifier)
        
        return vc as? T
    }
}

///Example
class MyViewController: UIViewController {
    
    lazy var otherVC: OtherViewController? = instantiateVC(by: .main)
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        
        if let vc =  otherVC {
            present(vc, animated: true)
        }
}