title: When should I use @synthesize explicitly?
body: <p>As far as I know, since XCode 4.4 the <code>@synthesize</code> will auto-generate the property accessors. But just now  I have read a sample of code about <code>NSUndoManager</code>, and in the code it noticed that the <code>@synthesize</code> is added explicitly. Like:</p>
  
  <pre><code>@interface RootViewController  ()
  
  @property (nonatomic, strong) NSDateFormatter *dateFormatter;
  @property (nonatomic, strong) NSUndoManager *undoManager;
  
  @end
  
  @implementation RootViewController
  //Must explicitly synthesize this
  @synthesize undoManager;
  </code></pre>
  
  <p>I am feeling puzzled now... When should I add <code>@synthesize</code> explicitly to my code?</p>