preg_replace_callback inside a class

<?php class MyClass {

  function preg_callback_url($matches)
  {
    //var_dump($matches);
    $url = $matches[1].$matches[2];
    $text = '';
    $pos = strpos($url,' ');
    if ($pos!==FALSE) {
      $text = trim(substr($url,$pos+1));
      $url = substr($url,0,$pos);
    }
    return '<a href="'.$url.'" rel="nofollow">'.(($text!='') ? $text : $url).'</a>';
  }

  function ParseText($text)
  {
    return preg_replace_callback('/\[(http|https|ftp)(.*?)\]/iS',array( &$this, 'preg_callback_url'), $text);
  }

} ?>