title: Issue with passing UIViewcontroller carrying delegate as parameter to swift function
body: <pre><code>class func invite(_cntrl : UIViewController) 
  {
    // code to open mail composer sheet
  }
  </code></pre>
  
  <p>this method needs to accept controllers which conforms to <strong><code>MFMailComposeViewControllerDelegate</code></strong>.</p>
  
  <p>currently it gives <strong>error</strong> : </p>
  
  <pre><code>Type 'UIViewController' does not conform to protocol 
  'MFMailComposeViewControllerDelegate'
  </code></pre>
  
  <p>how to pass uiviewconroller conforms <code>MFMailComposeViewControllerDelegate</code> ?</p>
  
  <p>something like :</p>
  
  <pre><code>class func invite(_cntrl : UIViewController&lt;MFMailComposeViewControllerDelegate&gt;)
  {
     // code to open mail composer sheet
  }
  </code></pre>