title: What does $0 and $1 mean in sorting in Swift 2.0
body: <p>Lots of people use <code>$0</code> and <code>$1</code> when sorting. It does not work for me. Here is the code that some people use.</p>
  
  <pre><code>images.sort({ $0.fileID &gt; $1.fileID })
  </code></pre>
  
  <p><code>images</code> is the array and I assume that <code>.fileID</code> is a field within that object. I want to sort my array of <code>oneCells</code> structs named <code>spend</code>.</p>
  
  <pre><code>struct oneCell{
      var date = NSDate()
      var money = Int()
  }
  
  var spend = [oneCell]()
  </code></pre>
  
  <p>I want to sort the array by date. How would I do that?</p>