protected function exists($key)
{
if (!array_key_exists($key, $this->items)) {
// key not in cache
return false;
}
$expire = $this->items[$key][1];
if ($expire !== 0 && $expire < time()) {
// not permanent & already expired
$this->size -= strlen($this->items[$key][0]);
unset($this->items[$key]);
return false;
}
$this->lru($key);
return true;
}