public function addInstance($key, $object = null)
    {
        if (\is_object($key)) {
            $this->storage->instance(\get_class($key), $key);
        } elseif (\is_object($object)) {
            $this->storage->instance($key, $object);
        } else {
            throw new ContainerException('An object instance must be passed');
        }
    }