php > $a = new stdClass();
php > $b = new stdClass();
php > $a->name = 'a';
php > $b->name = 'b';
php > function mod($o, $b) { $o = $b; return $o;}
php > print_r(mod($a, $b));
stdClass Object
(
    [name] => b
)
php > print_r($a);
stdClass Object
(
    [name] => a
)