title: PHP - Make reference parameter optional?
body: <p>Say I've defined a function in PHP, and the last parameter is passed by reference.  Is there any way I can make that optional? How can I tell if it's set?</p>
  
  <p>I've never worked with pass-by-reference in PHP, so there may be a goofy mistake below, but here's an example:</p>
  
  <pre><code>$foo;
  function bar($var1,&amp;$reference)
  {
      if(isset($reference)) do_stuff();
      else return FALSE;
  }
  
  bar("variable");//reference is not set
  bar("variable",$foo);//reference is set
  </code></pre>