public function removeItem($key) {
   if(isset($this->_members[$key])) {
      unset($this->_members[$key]);
   } else {
      throw new KeyInvalidException("Bdny klucz \"$key\"!");
   }
}

public function getItem($key) {
   if(isset($this->_members[$key])) {
      return $this->_members[$key];
   } else {
      throw new KeyInvalidException("Bdny klucz \"$key\"!");
   }
}