PHP是否在分配时复制对象？

Question

Does PHP duplicate an object when = is used or does it just create a new pointer that points to an already existing object?

Are both of these the same?

$obj1 = new object(); 
$obj2 = $obj1;

$obj1 = new object(); 
$obj2 = clone $obj1;

Answer 1

In PHP 4 (i.e. ancient history) objects were indeed copied on assignment. This was not helpful behaviour.

Since PHP 5, objects are now assigned by reference, unless they are cloned.

You can easily test this:

$obj1 = new object(); 
$obj2 = $obj1;
var_dump($obj1 === $obj2); // bool(true)

$obj1 = new object(); 
$obj2 = clone $obj1;
var_dump($obj1 === $obj2); // bool(false)