title: Swift optional method in protocol without objc
body: <p>I know, that making some methods in a Swift protocol requires to use <code>@objc protocol</code>. The problem is, that I can't use the objective c way, because I have a method in the protocol, which returns a Swift struct. So I'm getting the error, that I can't use the @objc protocol, because my method returns a result, which cannot be represented in objective c.</p>
  
  <p>Unfortunately, I absolutely want to use an optional methods, because there are two methods, which are alternative and the user of my class shall choose, which way he want to use.</p>