How do I create a copy of an object in PHP

Question

As far as I know, PHP objects are passed by reference.

<?php


class A {

    public $b;

}



function set_b($obj) { $obj->b = "after"; }


$a = new A();

$a->b = "before";

$c = $a; //i would especially expect this to create a copy.


set_b($a);


print $a->b; //i would expect this to show 'before'

print $c->b; //i would ESPECIALLY expect this to show 'before'


?>

How do I pass $a to set_b() by value, not by reference?