Question

The PHP reference manuals say that, when serializing an object, the methods will not be saved. (See http://www.php.net/manual/en/language.oop5.serialization.php, paragraph 1).

However, the first example given in the manual shows a method being serialised, then unserialised and used.

Isn’t this a contradiction? Am I missing something?

Answer 1

I must say, that I don’t see where a method is serialized in the first example. When serializing no methods are serialized, only the classname and the properties. You can see this, if you have a look at the serialized data

$ser = serialize($object);
var_dump($ser);

You will notice, that there is no method mentioned. However, if you unserialize an object, its recreated by the classname. Or in other words: You will get a new object, but with the values you serialized before.

Usually this is not as important as it sounds like, because usually the serialized/unserialized object should behave the same.

// serialize 
class A {
  public $a = null;
  public function test () {
    echo "Hello";
  }
}
$a = new A;
echo $a->test(); // "Hello"
$x = serialize($a);

// unserialize (somewhere else)
class A {
  public $a = null;
  public function test () {
    echo "World";
  }
}
$a = unserialize($x);
echo $a->test(); // "World"

Here the serializer uses a “wrong” class and the output is different, than the expected one. As long as you make sure there are no classname collisions you usually don’t need to think about it.