Hm, set an infinite time for the cache is not particularly convenient, in this case it will be convenient to only receive the contents of the cache.
If someone wants to set default lifetime this is still simple:
```php
$cache['config'] = array('db' => $db);
```
But if someone wants set custom lifetime:
```php
$cache['db.menu.1000'] = $menu;
// that is the same of
$cache->save('db.menu', $menu, 1000);
```