title: unrecognized selector sent to instance - Swift 4 only
body: <p>I'm having trouble understanding what this error means. My app was working fine until I migrated up to Swift 4. Now I'm getting this <code>tableView:numberOfRowsInSection</code> error when trying to open several of my view controllers. I didn't get any of these errors in Swift 3.2. The numberOfRowsInSection method has been implemented in all cases, and appears fine. Can anyone point me in the right direction?</p>
  
  <blockquote>
    <p>2017-11-26 10:21:04.973523-0600 Y2GOsp[27701:6382461]
    -[Y2GOsp.ClientDetailViewController tableView:numberOfRowsInSection:]: unrecognized selector sent to instance 0x7fa51c89f000 2017-11-26
    10:21:43.328635-0600 Y2GOsp[27701:6382461] *** Terminating app due to
    uncaught exception 'NSInvalidArgumentException', reason:
    '-[Y2GOsp.ClientDetailViewController
    tableView:numberOfRowsInSection:]: unrecognized selector sent to
    instance 0x7fa51c89f000'</p>
  </blockquote>
  
  <p>numberOfRowsInSection implementations:</p>
  
  <p>Example 1:</p>
  
  <pre><code>func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -&gt; Int {
      return 1
  }
  </code></pre>
  
  <p>Example 2:</p>
  
  <pre><code>func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -&gt; Int {
      return dayAppoints.count
  }
  </code></pre>