title: Correct way to access super in completion block
body: <p>I have a subclass of NSOperation which send a cancel request over a network. 
  I want to cancel operation only if the request was successful :</p>
  
  <pre>
  
  // overrider cancel of NSOperation
  -(void)cancel{
   [NSURLConnection sendAsynchronousRequest:request 
                                         queue:[NSOperationQueue mainQueue]
                             completionHandler:^(NSURLResponse *response, NSData *data, NSError *error) {
         [super cancel];
      }];
  }
  </pre>
  
  <p>Will this cause any retain cycle or something ? Do I need a weak Super (I am using ARC)</p>