could::getInstance

static function getInstance($userId = 0)
{
	$userId = intval($userId);
	if(!$userId)
	{
		$userId = User::getId();
	}

	if(!$userId)
	{
		throw new ArgumentException('User ID not defined');
	}

	if(!array_key_exists($userId, static::$instances))
	{
		static::$instances[$userId] = new static($userId);
	}

	return static::$instances[$userId];
}