<?php

class A implements Serializable {

  protected $foo = 'foo';
  protected $bar = 'bar';

  function getFoo() { return $this->foo; }
  function getBar() { return $this->bar; }

  public function serialize() {
    unset($this->foo);
    return serialize($this);
  }

  public function unserialize($data) {
    $this->foo = $data['foo'];
    $this->bar = $data['bar'];
  }

}

$a = new A();
var_dump($a);
$s = serialize($a);
var_dump($s);
var_dump($a);