Why does this code print "unknown type" and not "array"?

webuser@poe /home/www/servers/poe.shonline.de $ cgi/php
<?php
class auth { 
  var $auth = array(); 
 
  function auth() {
 
       printf("type = %s\n", gettype($this->auth));
  } 
}
 
$auth = new auth;
$auth->auth();
Content-type: text/html
 
type = unknown type