title: preg_replace_callback requires argument 2 to be a valid callback... Stuck!
body: <pre><code>public function make_url_clickable_cb($matches) {
  $ret = '';
  $url = $matches[2];
  
  if ( empty($url) )
      return $matches[0];
  // removed trailing [.,;:] from URL
  if ( in_array(substr($url, -1), array('.', ',', ';', ':')) === true ) {
      $ret = substr($url, -1);
      $url = substr($url, 0, strlen($url)-1);
  }
  return $matches[1] . "&lt;a href=\"$url\" rel=\"nofollow\"&gt;" . $this-&gt;truncate($url, 35, '...'). "&lt;/a&gt;" . $ret;
  }
  
  public function make_web_ftp_clickable_cb($matches) {
      $ret = '';
      $dest = $matches[2];
      $dest = 'http://' . $dest;
  
      if ( empty($dest) )
          return $matches[0];
      // removed trailing [,;:] from URL
      if ( in_array(substr($dest, -1), array('.', ',', ';', ':')) === true ) {
          $ret = substr($dest, -1);
          $dest = substr($dest, 0, strlen($dest)-1);
      }
      return $matches[1] . "&lt;a href=\"$dest\" rel=\"nofollow\"&gt;$dest&lt;/a&gt;" . $ret;
  }
  
  public function make_email_clickable_cb($matches) {
      $email = $matches[2] . '@' . $matches[3];
      return $matches[1] . "&lt;a href=\"mailto:$email\"&gt;$email&lt;/a&gt;";
  }
  public function make_clickable($ret) {
      $ret = ' ' . $ret;
      // in testing, using arrays here was found to be faster
      $ret = preg_replace_callback('#([\s&gt;])([\w]+?://[\w\\x80-\\xff\#$%&amp;~/.\-;:=,?@\[\]+]*)#is', 'Main::make_url_clickable_cb', $ret);
      $ret = preg_replace_callback('#([\s&gt;])((www|ftp)\.[\w\\x80-\\xff\#$%&amp;~/.\-;:=,?@\[\]+]*)#is', 'Main::make_web_ftp_clickable_cb', $ret);
      $ret = preg_replace_callback('#([\s&gt;])([.0-9a-z_+-]+)@(([0-9a-z-]+\.)+[0-9a-z]{2,})#i', 'Main::make_email_clickable_cb', $ret);
  
      // this one is not in an array because we need it to run last, for cleanup of accidental links within links
      $ret = preg_replace("#(&lt;a( [^&gt;]+?&gt;|&gt;))&lt;a [^&gt;]+?&gt;([^&gt;]+?)&lt;/a&gt;&lt;/a&gt;#i", "$1$3&lt;/a&gt;", $ret);
      $ret = trim($ret);
      return $ret;
  }
  </code></pre>
  
  <p>Why won't this work? 
  I get these errors: </p>
  
  <p>Warning: preg_replace_callback() [function.preg-replace-callback]: Requires argument 2, 'Main::make_url_clickable_cb', to be a valid callback in line 134</p>
  
  <p>Warning: preg_replace_callback() [function.preg-replace-callback]: Requires argument 2, 'Main::make_web_ftp_clickable_cb', to be a valid callback in line 135</p>
  
  <p>Warning: preg_replace_callback() [function.preg-replace-callback]: Requires argument 2, 'Main::make_email_clickable_cb', to be a valid callback in  line 136</p>