protected function prefixParentKeys($key, array $parent): string
    {
        return !empty($parent) ?
            $this->flattenKeys($parent).".$key" : $key;
    }
protected function prefixParentKeys($key, array $parent): string
    {
        return !empty($parent) ?
            $this->flattenKeys($parent).".$key" : $key;
    }
protected function prefixParentKeys ( $ key , array $ parent ) : string { return ! empty ( $ parent ) ? $ this -> flattenKeys ( $ parent ) . ".$key" : $ key ; }
Helper function to prefix all of the parent keys.

@param string $key
@param array  $parent

@return string
Helper function to prefix all of the parent keys .