title: Assert that viewController is both delegate and dataSource of its tableView
body: <p>As a sanity check, I would like to assert in <code>viewDidLoad</code> that a <code>UITableViewController</code> (i.e. <code>self</code>) is set both as <code>dataSource</code> and <code>delegate</code> of its <code>tableView</code>. How can I put this in Swift 3, where (unlike with Objective-C) additional type casts are needed? This still leads to syntax errors:</p>
  
  <pre><code>assert(tableView.dataSource == self)
  assert(tableView.delegate   == self)
  </code></pre>