__sleep and __wakeup example:
// example1.php
<?php
require 'file.class.php';
session_start();
$f = new File('/etc/hosts');
$f->seek(20);
$_SESSION['f'] = $f;
? >
// example2.php
<?php
require 'file.class.php';
session_start();
var_dump($_SESSION['f']);
? >