Description:
------------
When I use __set and __get methods on object i have set data to my object, and when i wanna get thows methods i would only get public methods that are non.

Same think is happened when i wanna example transfere Object to json format, there should be some way that i could get data that i wanna.

This could be very useful example using with Zend Framwork encoding a Database Table Row (http://framework.zend.com/manual/en/zend.db.table.row.html) where data is in private variable.

if not a Core function (that it should be in my opinion) then SPL interface would be needed.

Reproduce code:
---------------
class Test {
    protected $_data = array();
    public function __set($var, $value) {$this->_data[$var] = $value;}    
    public function __get($var) {
        if (isset($this->_data[$var])) {return $this->_data[$var]; }
        trigger_error('Undefined property: ' . __CLASS__ . '::$' . $var, E_USER_NOTICE);
        return null;
    }
    public function __isset($var) {return isset($this->_data[$var]);}
    
    public function __object_vars() {
        return $this->_data;
    }
}
$json = new Test();
$json->variable = 'value';

echo json_encode($json);

Expected result:
----------------
{"variable":"value"}

Actual result:
--------------
{}