Recursive array by array walk PHP

ArrayRecursiveWalker.php

<?php
declare(strict_types=1);

namespace App\Service\Walker;

/**
 * @author Kristijan Stipić 03092019
 */
class Walker
{
    /**
     * @author Kristijan Stipić 03092019
     * @param [type] $arr
     * @param \closure $manipulator
     * @return void
     */
    static public function array_recursive_walk_by_object(&$arr, \closure $manipulator) : void
    {
        if(\is_array($arr))
        {
            foreach($arr as $key => &$value)
            {
                $parent = &$arr[$key];
                if(\is_array($value) && !empty($value))
                {
                    /**
                     * @param $key string
                     * @param $value array
                     * @param $parent array
                     */
                    $manipulator($key, $value, $parent);
                    self::array_recursive_walk_by_object($value, $manipulator);
                }
            }
        }
    }
}

// Example:

$content = [
		'test' => [
				'key' => 'value',
				'key2' => 'value2',
				'key3' => [
					'key3.1' => 'value3.1'
				]
		]
];
$arr = 'nothing special';
Walker::array_recursive_walk_by_object($content, function($key, &$value, &$parent) use($arr)
{
		if(isset($value['key3']) && is_array($value['key3']))
		{
				$value['key3'] = [
				   'key3.1-changed' => 'value3.1-changed'
				];
		}
});