Delegation 2: extension

extension.swift

class FirstViewController: UIViewController {
    
    private let items : [String] = [ /* some items */]
    private let tableView = UITableView()
    
    /* lots of other methods */
    
    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        tableView.delegate = self
    }
    
}

extension FirstViewController: UITableViewDelegate {
    
    func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
        let item = items[indexPath.row]
        navigationController?.pushViewController(SecondController(item: item), animated: true)
    }
    
}