php class construct error แบบนี้ทำไงดี..php class construct error แบบนี้ทำไงดี..

<?php

class Random{
    private $text;
	function __construct($length){
		$text = "";
		$key_chars = '0123456789';
		$rand_max  = strlen($key_chars) - 1;
		for ($i = 0; $i < $length; $i++) {
			$rand_pos  = rand(0, $rand_max);
			$text.= $key_chars{$rand_pos};
			}
		$this->text = $text;
        }
       function __toString() {
           return $this->text;
       }
}
echo new Random(5);

?>