Collection class that can be used with Zend_Paginator

Collection.php

class Jg_Mapper_Collection implements Iterator, Countable, Zend_Paginator_Adapter_Interface {
  protected $_mapper;
  protected $_total;
  protected $_raw = array();
  protected $_domain_object_class;

  protected $_result;
  protected $_pointer = 0;
  protected $_objects = array();

  public function __construct(array $raw, Jg_Mapper $mapper, $domain_object_class) {
    $this->_raw = $raw;
    $this->_total = count($raw);
    $this->_mapper = $mapper;
    $this->_domain_object_class = $domain_object_class;
  }

  public function add($object) {
    if (!($object instanceof $this->_domain_object_class)) {
      throw new Exception('This is a "' . $this->_domain_object_class. '" collection');
    }
    $this->_objects[$this->count()] = $object;
    $this->_total++;
  }

  protected function _getRow($num) {
    $this->_notifyAccess($num);

    if ($num >= $this->_total || $num < 0) {
      return null;
    }
    if (!isset($this->_objects[$num]) && isset($this->_raw[$num])) {
      $this->_objects[$num] = $this->_mapper->createObject($this->_raw[$num]);
    }
    return $this->_objects[$num];
  }

  public function rewind() {
    $this->_pointer = 0;
  }

  public function current() {
    return $this->_getRow($this->_pointer);
  }

  public function key() {
    return $this->_pointer;
  }

  public function next() {
    $row = $this->_getRow($this->_pointer);
    if ($row) {
      $this->_pointer++;
    }
    return $row;
  }

  public function valid() {
    return !is_null($this->current());
  }

  public function count() {
    return $this->_total;
  }

  /**
   * Returns an array of items for a page. Called by Zend_Paginator.
   *
   * @param  integer $offset Page offset
   * @param  integer $itemCountPerPage Number of items per page
   * @return array
   */
  public function getItems($offset, $itemCountPerPage) {
    $this->_notifyAccess($offset, $itemCountPerPage);

    $items = array();
    for ($i = $offset; $i < ($offset + $itemCountPerPage); $i++) {
      $items[] = $this->_getRow($i);
    }
    return $items;
  }

  protected function _notifyAccess($offset, $length = 1) {
    // Empty on purpose. Child classes can extend to support lazy loading
  }
}