cviebrock / eloquent-sluggable

        $method = $config['method'];

        $maxLength = $config['maxLength'];

        if ($method === null) {

            $slugEngine = $this->getSlugEngine($attribute);

            $slug = $slugEngine->slugify($source, $separator);

        } elseif (is_callable($method)) {

            $slug = call_user_func($method, $source, $separator);

        } else {

            throw new \UnexpectedValueException('Sluggable "method" for ' . get_class($this->model) . ':' . $attribute . ' is not callable nor null.');

        }

        if (is_string($slug) && $maxLength) {

            $slug = mb_substr($slug, 0, $maxLength);

        }

        $method = $config['uniqueSuffix'];

        if ($method === null) {

            $suffix = $this->generateSuffix($slug, $separator, $list);

        } else if (is_callable($method)) {

            $suffix = call_user_func($method, $slug, $separator, $list);

        } else {

            throw new \UnexpectedValueException('Sluggable "reserved" for ' . get_class($this->model) . ':' . $attribute . ' is not null, an array, or a closure that returns null/array.');

        }

        return $slug . $separator . $suffix;

    }