title: Arrk! ARC error:'CFTypeRef' (aka 'const void *') to 'NSNumber *' is disallowed
body: <p>I'm trying to convert some Apple code (from <code>SquareCam</code> example) to ARC. I had the Apple code flagged to compile as non-ARC and it worked but I was getting crash errors passing images between the non-ARC context to an ARC context - so I'm trying to resolve that.</p>
  
  <p>Anyway, I think I have got all the ARC stuff handled except for this line:</p>
  
  <pre><code> NSNumber *orientation = CMGetAttachment(imageDataSampleBuffer, kCGImagePropertyOrientation, NULL);
  </code></pre>
  
  <p>This is used for the <code>CIDetectorImageOrientation</code> key value (CoreImage face detection). I get the ARC error below for this and none of the stuff I have tried resolves this. "imageDataSampleBuffer" is of type <code>CMSampleBufferRef</code>.</p>
  
  <p>What is the correct way to convert the CFTypeRef to the NSNumber I need? - Thanks!</p>
  
  <blockquote>
    <p>Implicit conversion of a non-Objective-C pointer type 'CFTypeRef' (aka
    'const void *') to 'NSNumber *' is disallowed with ARC</p>
  </blockquote>