public function get($serviceType, $refInstance = null)
    {
        if (!isset($this->services[$serviceType::getName()])) {
            if (is_null($refInstance)) {
                $this->services[$serviceType::getName()] = new $serviceType();
            } else {
                $this->services[$serviceType::getName()] = new $serviceType($refInstance);
            }
        }
        return $this->services[$serviceType::getName()];
    }