Add an item to the server only if such key doesn't exist at the server yet.
string $key:
mixed $value:
integer $expiration:
boolean
public function add($key, $value, $expiration = 0) {
if (!$this->connected) {
return false;
}
if (!isset($this->storage[$key])) {
$this
->storeData($key, $value);
return true;
}
return false;
}