title: Can't get reference to an UIViewcontroller
body: <p>I have this:</p>
  
  <pre><code>guard let mapVC = mapSB.instantiateInitialViewController() else { return }
  
  mapVC.navigationItem.title = "Some title string"
  //        (mapVC as! MapViewController).string = "Some string"
  //        (mapVC.navigationController?.viewControllers.first as! MapViewController).string = "Some string"
  </code></pre>
  
  <p>I have tried both of the commented out lines, but it crashes on whichever line I comment back in. And here is the po of mapVC:</p>
  
  <pre><code>po mapVC
  error: &lt;EXPR&gt;:3:1: error: use of unresolved identifier 'mapVC'
  mapVC
  ^~~~~~~~~
  </code></pre>
  
  <p>Which is weird, because it does correctly set the mapVC.navigationItem.title as "Some title string."</p>
  
  <p>If this helps, mapVC is embedded in a navigation controller in mapSB.</p>
  
  <p>Edit:</p>
  
  <p>The crash message is:</p>
  
  <pre><code>Thread 1: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
  </code></pre>
  
  <p>And mapVC is of type MapViewController, hence the casting.</p>