title: Compiler error when using `enumerateObjectsUsingBlock` of PHFetchResult
body: <p>I met the following compile error:</p>
  
  <blockquote>
    <p>Cannot invoke 'enumerateObjectsUsingBlock' with an argument list of
    type '((_, _, _) -> Void)'</p>
  </blockquote>
  
  <p>I think it may be easier to understand my situation with this screenshot of XCode6.3.</p>
  
  <p><img src="https://i.stack.imgur.com/pypj7.png" alt="enter image description here"></p>
  
  <p>This codes is for testing the fetching of PHAsset objects using the <code>fetchAssetsWithMediaType</code> method. As you may know, this method returns PHFetchResult which has enumeration methods. I tried to enumerate all object in the result by <code>enumerateObjectsUsingBlock</code>. Unfortunately, the Swift compiler gave me an error. After a long investigation, I ended up making a conclusion that this code is correct.</p>
  
  <p>For your information, the above code is found by googling for testing PHAsset.</p>