title: necessary to initialize NSSet?
body: <p>They changed some things with Xcode 4, so I was wondering if I needed to initialize an NSSet by</p>
  
  <pre><code>NSMutableSet *variablesUsed = [NSMutableSet set];
  </code></pre>
  
  <p>or is</p>
  
  <pre><code>NSMutableSet *variablesUsed;
  </code></pre>
  
  <p>sufficient? Or does the second option initialize to nil? Is that the same as empty set?</p>
  
  <p>Thanks for your help!</p>