title: @available - make only available on OS X
body: <p>Is it possible to mark a function/computed variable as available on OS X and unavailable on iOS (and vice versa)? Something such as <code>@available(OSX 10.0, iOS unavailable)</code>.</p>
  
  <p>I know about the <code>#if OSX</code> statement, however, I'm trying to achieve something that Apple has done for the <code>NSURLThumbnailKey</code> - it's marked as <code>NS_AVAILABLE_MAC(10_10);</code> in ObjC and the compiler will complain that the symbol is unavailable rather than that the compiler cannot resolve the symbol.</p>
  
  <p>Also, I've found that the <code>#if</code> statements in Swift are buggy, for example, defining <code>func myFunc(_, arg1:)</code> and <code>func myFunc(_, somethingElse:)</code> within the <code>#if</code> scope will result in an error saying that <code>myFunc</code> has already been defined. Which is why I'm trying to avoid using <code>#if</code>.</p>