title: How do I subclass NSDate?
body: <p>I first time tried to subClassed an NSDate to give it 2 methods that I need. Compiles fine, but in runtime I try to access it I get an error.</p>
  
  <p>Lets say I just want the current date which is unmodified in the subClass:</p>
  
  <pre><code>[myNSDate date];
  </code></pre>
  
  <p>I get the error</p>
  
  <pre><code>-[NSDate initWithTimeIntervalSinceReferenceDate:]: method only defined for 
   abstract class.  Define -[myNSDate initWithTimeIntervalSinceReferenceDate:]!
  </code></pre>
  
  <p>what is different? </p>