public function isClass($className)
    {
        foreach ($this->definitions as $key => $value) {
            if (!strcasecmp($key, $className) && 'class' === $value->getType()) {
                return true;
            }
        }

        /*
         * Try to autoload the class from an external dependency
         */
        if (\count($this->externalDependencies)) {
            foreach ($this->externalDependencies as $namespace => $location) {
                if (preg_match('#^'.$namespace.'\\\\#i', $className)) {
                    return $this->loadExternalClass($className, $location);
                }
            }
        }

        return false;
    }