title: "'NSOffState' is unavailable in Swift"
body: <p>I have an extension of NSView with a simple function called clearControllersInView() which takes all the controllers in the view and sets them to a default value (i.e. checkboxes to off, popups and combos to first menu item, textfields to empty string).  I had no problems with this under Swift 3.</p>
  
  <p>I'm using the current beta of Xcode 9 and updating this extension to Swift 4.  The problem is in the section handling checkboxes where I'm getting the error "'NSOffState' is unavailable in Swift" when trying to set the checkbox to NSOffState:</p>
  
  <pre><code>if item is NSButton {
      let checkbox = item as? NSButton
      checkbox?.state = **NSOffState**  -- *'NSOffState' is unavailable in Swift*
  }
  </code></pre>
  
  <p>I was getting the same error elsewhere in this program where I check the value of a checkbox.  I was able to temporarily fix those instances by checking against the controllers raw value:<br>
      if checkbox.state == NSOnState -- <em>error</em><br>
      if checkbox.state.rawValue == 1 -- <em>no error</em>  </p>
  
  <p>Wasn't able to find a solution by searching here or Google in general.  Any help would be greatly appreciated!</p>