title: How to convert this code from Objective-C to Swift?
body: <pre><code>   [self.navigationItem.leftBarButtonItems enumerateObjectsUsingBlock:^(UIBarButtonItem* item, NSUInteger i, BOOL *stop) {
          item.customView.alpha = alpha;
      }];
      [self.navigationItem.rightBarButtonItems enumerateObjectsUsingBlock:^(UIBarButtonItem* item, NSUInteger i, BOOL *stop) {
          item.customView.alpha = alpha;
      }];
  </code></pre>
  
  <p>How to convert this block of code to Swift ? thanks.</p>