title: How to use instance method as callback for function which takes only func or literal closure
body: <p>In "ViewController.swift" I am creating this callback:</p>
  
  <pre><code>func callback(cf:CFNotificationCenter!, 
      ump:UnsafeMutablePointer&lt;Void&gt;, 
      cfs:CFString!, 
      up:UnsafePointer&lt;Void&gt;, 
      cfd:CFDictionary!) -&gt; Void {
  
  }
  </code></pre>
  
  <p>Using this observer:</p>
  
  <pre><code>CFNotificationCenterAddObserver(CFNotificationCenterGetDarwinNotifyCenter(), 
      nil, 
      self.callback, 
      "myMESSage", 
      nil, 
      CFNotificationSuspensionBehavior.DeliverImmediately)
  </code></pre>
  
  <p>Results in this compiler error:  </p>
  
  <blockquote>
    <p>"A C function pointer can only be formed from a reference to a 'func' or a literal closure"</p>
  </blockquote>