public function is_valid()
    {
        $isauthority = $this->iuserinfo !== null || $this->ihost !== null || $this->port !== null;
        if ($this->ipath !== '' &&
            (
                $isauthority && (
                    $this->ipath[0] !== '/' ||
                    substr($this->ipath, 0, 2) === '//'
                ) ||
                (
                    $this->scheme === null &&
                    !$isauthority &&
                    strpos($this->ipath, ':') !== false &&
                    (strpos($this->ipath, '/') === false ? true : strpos($this->ipath, ':') < strpos($this->ipath, '/'))
                )
            )
        )
        {
            return false;
        }

        return true;
    }