title: Are _Nullable and _Nonnull useful for anything other than Swift interop?
body: <p>Does the Objective-C compiler actually warn you if it thinks that you may be passing <code>nil</code> to a parameter marked with <code>_Nonnull</code>?</p>
  
  <p>Or is it merely a hint to whatever tool converts between Swift and Objective-C to better deal with Swift optionals?</p>