Extend the \DateInterval class to have a __toString() method, returning the string representation of the object

DateTimeInterval.php

<?php

use DateInterval;

class DateTimeInterval extends DateInterval
{
    /**
     * Return the textual representation of an interval object
     *
     * @return string
     */
    public function __toString(): string
    {
        $dateParts = array_filter([
            'Y' => $this->y,
            'M' => $this->m,
            'D' => $this->d
        ]);
        $timeParts = array_filter([
            'H' => $this->h,
            'M' => $this->i,
            'S' => $this->s
        ]);

        $string = 'P';

        if (!empty($dateParts)) {
            foreach ($dateParts as $which => $val) {
                $string .= sprintf('%d%s', $val, $which);
            }
        }
        if (!empty($timeParts)) {
            $string .= 'T';
            foreach ($timeParts as $which => $val) {
                $string .= sprintf('%d%s', $val, $which);
            }
        }

        return $string;
    }
}