import UIKit

protocol NibInitiable {
    static func loadFromNib() -> Self?
    static func loadFromNibForced() -> Self
}

extension NibInitiable where Self : UIViewController {
    static func loadFromNib() -> Self? {
        return UIViewController(nibName: String(describing: self), bundle: Bundle.main) as? Self
    }

    static func loadFromNibForced() -> Self {
        guard let vc = loadFromNib() else { fatalError("Couldn't load \(String(describing:self)) from nib.") }
        return vc
    }
}

class C2MViewController : UIViewController, NibInitiable { }
class MediumViewController : UIViewController, NibInitiable { }

let vc = C2MViewController.loadFromNib()                // C2MViewController?
let vcForced = C2MViewController.loadFromNibForced()    // C2MViewController

let anotherVC = MediumViewController.loadFromNib()              // MediumViewController?
let anotherVCForced = MediumViewController.loadFromNibForced()  // MediumViewController