如何向Laravel Carbon添加自定义方法[已解决]

Question

我已经搜索此问题2天了，但是没有运气。我想向laravel carbon添加自定义方法。我使用以下语法：

namespace App\Http\Controllers\Helpers;

use Carbon\CarbonInterface;

interface CarbonJalaliInterface extends CarbonInterface {

    public function toJalaliDateTimeString($unitPrecision = 'second');
    public function toJalaliDateString($unitPrecision = 'second');

}

abstract class CarbonJalali implements CarbonJalaliInterface {

    public function toJalaliDateTimeString($unitPrecision = 'second') {
        list($part1, $part2) = explode(' ', $this->rawFormat('Y-m-d '.static::getTimeFormatByPrecision($unitPrecision)));
        list($year, $month, $day) = explode('-', $part1);
        list($hour, $minute, $second) = explode(':', $part2);
        $timestamp = mktime($hour, $minute, $second, $month, $day, $year);
        include_once ('jdf.php');
        $jalali_date = jdate("H:i:s - Y/m/d",$timestamp);
        return $jalali_date;
    }

    public function toJalaliDateString($unitPrecision = 'second') {
        $timezone = 0;
        list($part1, $part2) = explode(' ', $this->rawFormat('Y-m-d'));
        list($year, $month, $day) = explode('-', $part1);
        $timestamp = mktime($month, $day, $year);
        include_once ('jdf.php');
        $jalali_date = jdate("Y/m/d",$timestamp);
        return $jalali_date;
    }

}

但是我得到了错误：

Symfony\Component\Debug\Exception\FatalErrorException DateTimeInterface can't be implemented by user classes

我想这样使用它：

CarbonJalali::now()->toJalaliDateTimeString();

有什么建议吗？谢谢。

已解决

由于@lagbox，因此无需使用实现，其工作语法如下：

namespace App\Http\Controllers\Helpers;
class CarbonJalali extends Carbon {

public function toJalaliDateTimeString($unitPrecision = 'second') {
        list($part1, $part2) = explode(' ', $this->rawFormat('Y-m-d '.static::getTimeFormatByPrecision($unitPrecision)));
        list($year, $month, $day) = explode('-', $part1);
        list($hour, $minute, $second) = explode(':', $part2);
        $timestamp = mktime($hour, $minute, $second, $month, $day, $year);
        include_once ('jdf.php');
        $jalali_date = jdate("H:i:s - Y/m/d",$timestamp);
        return $jalali_date;
    }

    public function toJalaliDateString($unitPrecision = 'second') {
        $timezone = 0;
        list($part1, $part2) = explode(' ', $this->rawFormat('Y-m-d'));
        list($year, $month, $day) = explode('-', $part1);
        $timestamp = mktime($month, $day, $year);
        include_once ('jdf.php');
        $jalali_date = jdate("Y/m/d",$timestamp);
        return $jalali_date;
    }

}