iSerializable vs __sleep

<?PHP

    ABSTRACT CLASS BaseClass
    {

        public function __sleep()
        {
            print __METHOD__.' called'."\n";
            $defaults   = get_class_vars(get_class($this));
            $present    = get_object_vars($this);
            $result     = [];

            foreach($present as $key => $value)
                if(!is_resource($value)
                && (is_object($value) || is_array($value) || $defaults[$key] !== $value))
                    $result[] = $key;

            print print_r($result)."\n\n";

            return $result;
        }
    }


    Class NonSerializeClass Extends BaseClass
    {
        public  $_____baz       = 'foo';
        private $__array        = [];

        public function __construct(array $array = array())
        {
            $this->_____baz = 'bar';
            $this->__array = $array;
        }
    }

    Class SerializeClass Extends BaseClass implements \Serializable
    {

        private static $__serializable  = ['__array', '__offsets', '__indexes', '__protMode'];
        public  $_____baz       = 'foo';
        private $__array        = [];
        private $__offsets      = [];
        private $__indexes      = [];
        private $__protMode     = 0;
        private $__itIndex      = 0;

        public function serialize()
        {
            $result = [];
            foreach(self::$__serializable as $property)
                $result[$property] = $this->$property;

            return serialize($result);
        }

        public function unserialize($serialized)
        {
            $unserialized = unserialize($serialized);
            foreach(self::$__serializable as $field)
                $this->$field = $unserialized[$field];

            return $this;
        }

        public function __construct(array $array = array())
        {
            $this->_____baz = 'bar';
            $this->__array = $array;
        }
    }

$a = new NonSerializeClass(["The" => "quick", 7 => "fox", "jumps" => "over", "the" => "lazy", "dog" => '.']);
$b = new SerializeClass(["The" => "quick", 7 => "fox", "jumps" => "over", "the" => "lazy", "dog" => '.']);

//var_dump($a, $b);

$_a = serialize($a);
$_b = serialize($b);

$__a = unserialize($_a);
$__b = unserialize($_b);
var_dump($__a, $__b);


?>
localhost\illiFW\dev\BaseClass::__sleep called
Array
(
    [0] => _____baz
)
1

object(localhost\illiFW\dev\NonSerializeClass)#5 (2) {
  ["_____baz"]=>
  string(3) "bar"
  ["__array":"localhost\illiFW\dev\NonSerializeClass":private]=>
  array(0) {
  }
}
object(localhost\illiFW\dev\SerializeClass)#6 (6) {
  ["_____baz"]=>
  string(3) "foo"
  ["__array":"localhost\illiFW\dev\SerializeClass":private]=>
  array(5) {
    ["The"]=>
    string(5) "quick"
    [7]=>
    string(3) "fox"
    ["jumps"]=>
    string(4) "over"
    ["the"]=>
    string(4) "lazy"
    ["dog"]=>
    string(1) "."
  }
  ["__offsets":"localhost\illiFW\dev\SerializeClass":private]=>
  array(0) {
  }
  ["__indexes":"localhost\illiFW\dev\SerializeClass":private]=>
  array(0) {
  }
  ["__protMode":"localhost\illiFW\dev\SerializeClass":private]=>
  int(0)
  ["__itIndex":"localhost\illiFW\dev\SerializeClass":private]=>
  int(0)
}