public function getInstallScript()
    {
        if (! $this->installScript) {
            $installClass = $this->installNamespace.'Install';

            if (! class_exists($installClass)) {
                $message = sprintf('No install class found at %s. Nothing to do.', $installClass);

                throw new RuntimeException($message);
            }

            $installScript = new $installClass;

            $this->installScript = $installScript;
        }

        return $this->installScript;
    }