title: Downcast from Any to a protocol
body: <p>I have the following code. How can I resolve the error in the last line?</p>
  
  <pre><code>protocol Animal {
      func walk()
  }
  
  struct Cat: Animal {
      func walk() {}
  
      init() { }
  }
  
  var obj: Any = Cat()
  var cat = obj as Animal // ERROR: cannot downcast from Any to unrelated type Animal
  </code></pre>