title: Error: Ambiguous reference to member 'subscript' in Swift 3
body: <p>I downloaded the Xcode 8 beta and converted my syntax to Swift 3. When I did, I got the eponymous error with this code (this didn't happen before):</p>
  
  <p>Swift 3:</p>
  
  <pre><code>do {
      let fileAttributes = try FileManager.default().attributesOfItem(atPath: fileURL.path!) // Error here
      let fileSizeNumber = fileAttributes[NSFileSize] as! NSNumber
      fileSize = fileSizeNumber.longLongValue
  } catch _ as NSError {
      print("Filesize reading failed")
  }
  </code></pre>
  
  <p>Swift 2:</p>
  
  <pre><code>do {
      let fileAttributes = try NSFileManager.defaultManager().attributesOfItemAtPath(fileURL.path!)
      let fileSizeNumber = fileAttributes[NSFileSize] as! NSNumber
      fileSize = fileSizeNumber.longLongValue
  } catch _ as NSError {
      print("Filesize reading failed")
  }
  </code></pre>
  
  <p>Is this a bug in Swift 3, or am I missing something?</p>
  
  <p>I know there are many questions about the same error, but those don't fix my problem. I'm happy to edit for clarification.</p>
  
  <p>Thanks in advance!</p>