Sort files in the folder by their file size and retrieve it as an array

Sizer.php

<?php

/**
 * @author https://gist.github.com/sutlxwhx
 *
 * @version 0.2
 *
 * @license Apache License 2.0
 *
 */

namespace sutlxwhx;

class Sizer
{
    /**
     * @var string Set the property that will store the result
     */
    public $result;

    /**
     * Sizer constructor.
     * @param $folder_name Absolute path to the folder which you want to process
     */
    public function __construct($folder_name)
    {
        $this->working_folder = $folder_name . DIRECTORY_SEPARATOR;
        if ($this->validate()) {
            return $this->result = $this->process();
        } else {
            return $this->result = "Directory that you entered in not readable by the script. Check the reading permissions or if it even exists.";
        }
    }

    /**
     *  Check the availability of the input directory using ternary operators
     */
    private function validate()
    {
        return is_readable($this->working_folder) ? true : false;
    }

    /**
     *  Specify the evaluating process
     */
    private function process()
    {
        $list_of_files = array_values(array_diff(scandir($this->working_folder), array('..', '.')));
        foreach ($list_of_files as $filename) {
            $list_of_file_sizes["$filename"] = filesize($this->working_folder . $filename);
        }
        arsort($list_of_file_sizes, SORT_NATURAL);
        $list_of_files = array_values(array_flip($list_of_file_sizes));
        return $list_of_files;
    }

}

/**
 *  Initialise Sizer class and set the necessary parameter
 *  Dump the result element of an object
 */
/* $sizer_worker = new Sizer(__DIR__ . DIRECTORY_SEPARATOR . 'test'); */
/* var_dump($sizer_worker->result); */