title: Private methods in a Category, using an anonymous category
body: <p>I'm creating a category over NSDate. It has some utility methods, that shouldn't be part of the public interface.</p>
  
  <p>How can I make them private? </p>
  
  <p>I tend to use the "anonymous category" trick when creating private methods in a class:</p>
  
  <pre><code>@interface Foo()
  @property(readwrite, copy) NSString *bar;
  - (void) superSecretInternalSaucing;
  @end
  
  @implementation Foo
  @synthesize bar;
  .... must implement the two methods or compiler will warn ....
  @end
  </code></pre>
  
  <p>but it doesn't seem to work inside another Category:</p>
  
  <pre><code>@interface NSDate_Comparing() // This won't work at all
  @end
  
  @implementation NSDate (NSDate_Comparing)
  
  @end
  </code></pre>
  
  <p>What's the best way to have private methods in a Category?</p>