Я тестировал и получил следующее:
class A {
public $property;
}
function set_property($obj) {
$obj->property = "after";
var_dump($obj);
}
$a = new A();
$a->property = "before";
// Creates a new Object from $a. Like "new A();"
$b = new $a;
// Makes a Copy of var $a, not referenced.
$c = clone $a;
set_property($a);
// object(A)#1 (1) { ["property"]=> string(5) "after" }
var_dump($a); // Because function set_property get by reference
// object(A)#1 (1) { ["property"]=> string(5) "after" }
var_dump($b);
// object(A)#2 (1) { ["property"]=> NULL }
var_dump($c);
// object(A)#3 (1) { ["property"]=> string(6) "before" }
// Now creates a new obj A and passes to the function by clone (will copied)
$d = new A();
$d->property = "before";
set_property(clone $d); // A new variable was created from $d, and not made a reference
// object(A)#5 (1) { ["property"]=> string(5) "after" }
var_dump($d);
// object(A)#4 (1) { ["property"]=> string(6) "before" }
?>