public function provideSymfonyService($name, $symfonyName = null)
    {
        if (null === $symfonyName) {
            $symfonyName = $name;
        }

        if (parent::offsetExists($name)) {
            throw new \LogicException(sprintf('Service %s has already been defined.', $name));
        }

        $this->delegates[$name] = $symfonyName;
    }