Class not found

[eluser]phpoet[/eluser]
I often put simple authentication checks in the constructor of my Controller. For example, if I were coding a blog, I might do something like this.

Code:

class Blog extends Controller {

  /**
   * Check authentication before executing any actions
   */
  public function __construct() {
    parent::__construct();
    $this->_check_authentication();
  }

  /**
   * Only allow unauthenticated access to a
   * the sign_in and register actions
   */
  private function _check_authentication() {
    $exceptions = array("sign_in", "register");
    $action = $this->uri->segment(2);
    if(!in_array($action, $exceptions)) {
      if(!$this->session->userdata('logged_in')) {
        $this->session->sess_destroy();
        redirect('blog/sign_in');
      }
    }
  }

}