title: variable was written, but never read?
body: <p>Im getting the following warning <code>variable 'isTaken' was written to, but never read</code> on the following code :</p>
  
  <pre><code>func textFieldShouldEndEditing(textField: UITextField) -&gt; Bool {
  
          var isTaken: Bool = false
  
          if textField == usernameTxt { var query = PFQuery(className: "_User")
          query = PFQuery(className: "_User")
          query.whereKey("username", equalTo: usernameTxt.text!)
          query.findObjectsInBackgroundWithBlock {
              (objects: [AnyObject]?, error: NSError?) in
              if error == nil {
                  if (objects!.count &gt; 0){
  
                      isTaken = true
  
                      }
                  } else {
                      print("Username is available. ")
                  }
              } else {
                  print("error")
              }
            }
          }
          return true
      }
  </code></pre>
  
  <p>why am I getting the warning and how do I do away with it?</p>