PHPでオブジェクトを配列に変換する方法

<?php
class foo
{
    function do_foo()
    {
        echo "Doing foo."; 
    }
}

$bar = new foo;
$bar->do_foo();
print_r((array)$bar);
?>

Doing foo.Array ( )

get_object_vars ( object $obj )

<?php
class Point2D {
    var $x, $y;
    var $label;

    function Point2D($x, $y)
    {
        $this->x = $x;
        $this->y = $y;
    }

    function setLabel($label)
    {
        $this->label = $label;
    }

    function getPoint()
    {
        return array("x" => $this->x,
                     "y" => $this->y,
                     "label" => $this->label);
    }
}

// "$label" is declared but not defined
$p1 = new Point2D(1.233, 3.445);
print_r(get_object_vars($p1));

$p1->setLabel("point #1");
print_r(get_object_vars($p1));

?>

 Array
 (
     [x] => 1.233
     [y] => 3.445
     [label] =>
 )

 Array
 (
     [x] => 1.233
     [y] => 3.445
     [label] => point #1
 )