title: What is a 'non-nominal type' in Swift?
body: <p>I see this error when trying to extend unorthodox 'types' like <code>(Int, Int)</code>, or <code>Any</code>:</p>
  
  <blockquote>
    <p>Non-nominal type 'Any' cannot be extended</p>
  </blockquote>
  
  <p>So what makes a type non-nominal? What's the difference between a non-nominal type like <code>Any</code> or <code>(Int)</code> and a regular nominal type like <code>Int</code>?</p>