title: Loop over a NSDictionary with swift
body: <p>I don't understand why this piece of Objective-C code:</p>
  
  <pre><code>id object = nil;
  NSEnumerator *enumerator = ...;
  while ((object = [enumerator nextObject])) {...}
  </code></pre>
  
  <p>can't be translated in Swift like this:</p>
  
  <pre><code>var key:AnyObject!
  let enumerator:NSEnumerator = myNSDictionary.keyEnumerator()    
  while ( (object = enumerator.nextObject()) ) {...}
  </code></pre>
  
  <p>I have this error :</p>
  
  <blockquote>
    <p>Type '()' does not conform to protocol 'BooleanType'</p>
  </blockquote>