title: Iterating over an NSMutableArray in Swift
body: <p>I'm trying to iterate over an NSMutableArray and it seems to behave differently than NSArray (at least in XCode 6 beta 3)</p>
  
  <pre><code>class Element : NSObject { }
  
  let a = NSArray()
  let ma = NSMutableArray()
  
  for e in a as Element[] { }
  for e in ma as Element[] { } // compiler error: Cannot convert the expression's type 'Element[]' to type 'Element[]'
  for e in ma as NSArray as Element[] { }
  </code></pre>
  
  <p>I'm confused why this is happening. Is there an explanation for this behavior or is this an XCode/Swift bug?</p>