Example of CodeIgniter Form_validation subclass

MY_Form_validation.php

<?php if (!defined('BASEPATH')) exit('No direct script access allowed');
/* app/libraries/MY_Form_validation */

class MY_Form_validation extends CI_Form_validation {
  function __construct() {
    parent::__construct();
  }

  protected function _execute($row, $rules, $postdata = NULL, $cycles = 0) {
    if (preg_match("/(required_if)/", implode(' ', $rules), $temp)) {
      $temp = $rules;

      foreach ($rules as $key=>$rule) {
        if (substr($rule, 0, 11) == 'required_if') {
          preg_match("/(.*?)\[(.*)\]/", $rule, $match);
          if ($this->required_if($postdata, $match[2])) {
            $temp[] = 'required';
            break;
          }

          unset($temp[$key]);
        }
      }

      $rules = $temp;
    }

    return parent::_execute($row, $rules, $postdata, $cycles);
  }

  function add_error($field, $error) {
    $this->_error_array[$field] = $error;
  }

  function required_if($str, $params) {
    $CI = &get_instance();

    list($classProp, $func) = explode(',', $params);

    return call_user_func(array($CI->$classProp, $func));
  }

  /**
   * @desc Validates a date format
   * @params format,delimiter
   * e.g. d/m/y,/ or y-m-d,-
   */
  function valid_date($str, $params) {
    // setup
    $CI =&get_instance();
    $params = explode(',', $params);
    $delimiter = $params[1];
    $date_parts = explode($delimiter, $params[0]);

    // get the index (0, 1 or 2) for each part
    $di = $this->valid_date_part_index($date_parts, 'd');
    $mi = $this->valid_date_part_index($date_parts, 'm');
    $yi = $this->valid_date_part_index($date_parts, 'y');

    // regex setup
    $dre =   "(0?1|0?2|0?3|0?4|0?5|0?6|0?7|0?8|0?9|10|11|12|13|14|15|16|17|18|19|20|21|22|23|24|25|26|27|28|29|30|31)";
    $mre = "(0?1|0?2|0?3|0?4|0?5|0?6|0?7|0?8|0?9|10|11|12)";
    $yre = "([0-9]{4})";
    $red = ''.$delimiter; // escape delimiter for regex
    $rex = "/^[0]{$red}[1]{$red}[2]/";

    // do replacements at correct positions
    $rex = str_replace("[{$di}]", $dre, $rex);
    $rex = str_replace("[{$mi}]", $mre, $rex);
    $rex = str_replace("[{$yi}]", $yre, $rex);

    if (preg_match($rex, $str, $matches)) {
      // skip 0 as it contains full match, check the date is logically valid
      if (checkdate($matches[$mi + 1], $matches[$di + 1], $matches[$yi + 1])) {
        return true;
      } else {
        // match but logically invalid
        $CI->form_validation->set_message('valid_date', "The date is invalid.");
        return false;
      }
    }

    // no match
    $CI->form_validation->set_message('valid_date', "The date format is invalid. Use {$params[0]}");
    return false;
  }

  function valid_date_part_index($parts, $search) {
    for ($i = 0; $i <= count($parts); $i++) {
      if ($parts[$i] == $search) {
        return $i;
      }
    }
  }
}