title: Swift 3 - append an array as 1 item into another array
body: <p>while this link: <a href="https://stackoverflow.com/questions/24002733/add-an-element-to-an-array-in-swift">Add an element to an array in Swift</a>
  shows how to add an item to an array, my question is about adding an array as an item to another array.</p>
  
  <p>I did not find any similar question - I have these arrays:</p>
  
  <p><code>[1,2,3]</code> and <code>[4,5,6]</code></p>
  
  <p>I want to append the first array to the other one as a whole, so I get this result:</p>
  
  <pre><code>[4,5,6,[1,2,3]]
  </code></pre>
  
  <p>Please note that this is <em>NOT</em> expected result:</p>
  
  <pre><code>[4,5,6,1,2,3]
  </code></pre>
  
  <p>How would I achieve this?</p>