title: What does $0 represent in closures in Swift?
body: <p>I have seen closures in Swift use <code>$0</code> internally and sometimes they use <code>$1</code>. What exactly is <code>$0</code> and what are other <code>$X</code> can you use?</p>
  <p>Here are examples of it in use:</p>
  <pre><code>applyMutliplication(2, {$0 * 3})
  array.map({$0 + 1})
  </code></pre>