getter und Setter erklärung gesucht

[h3ll]

funktioniert:

class foo {
    private $data = array();
    private $something = 123;

    public function __get($name) {
        return $data[$name];
    }

    public function __set($name, $value) {
        $this->data[$name] = $value;
    }
}

$obj = new foo();
$obj->somebody = 'Hello';
$obj->something = 'World'; 

Wirft einen Fatal Error:

class bar {
    private $something = 123;
}

$obj = new bar();
$obj->somebody = 'Hello';
$obj->something = 'World';
// Fatal error: Cannot access private property bar::$something in ... on line ...