title: What is the meaning of the '#' mark in swift language
body: <p>I have seen code like this:</p>
  
  <pre class="lang-js prettyprint-override"><code>func hello(name: String, #helloMessage: String) -&gt; String { 
      return "\(helloMessage), \(name)." 
  } 
  </code></pre>
  
  <p>My question is what <code>#</code> mark means before parameter's name? Is that meaning that the parameter has to be specified when calling a function?</p>
  
  <p>Moreover can anyone show me a difference with the function without this <code>#</code> mark? Code examples are more than welcome.</p>