smarty3 caching

[philas]

i'm use smarty 3 and write

$smarty = new Smarty();
$smarty->config_dir='./smarty/sconfigs/';
$smarty->template_dir='./templates/new/';
$smarty->compile_dir='./smarty/stemplates_c/';
$smarty->cache_dir='./smarty/scache/';

if(!$smarty->isCached('index.tpl','default')) {
   $smarty->assign("u",refresh_user_info(),true);    
}        
$smarty->display('index.tpl','default'); 

 

but {$u} is missing when i add if($smarty->isCached

 

help please!