static function undefined_function($function_name)
{
if (function_exists($function_name)) {
return new \Twig_SimpleFunction($function_name, function () use($function_name) {
ob_start();
$return = call_user_func_array($function_name, func_get_args());
$echo = ob_get_clean();
return empty($echo) ? $return : $echo;
}, array('is_safe' => array('all')));
}
return false;
}