Smarty (and other tpl ngins): assign and assign_by_ref

Question

This is not just about Smarty, but I guess most template engines that have variables assigned. It\'s more a theoretical question, than a practical. I have no use case.

Answer 1

As mentioned in other answers, PHP employs copy-on-write. However I do wish to answer this part of your post:

Objects are always, automatically assigned by reference.

This is not entirely true. They are assigned an identifier which points to an object.

$a = new stdClass();
$b = $a; // $a and $b now share same identifier
$b = 0; // $b no longer contains identifier
var_dump($a); // outputs object

Contrast this with assigning by reference:

$a = new stdClass();
$b =& $a; // $a and $b now share same reference
$b = 0; //
var_dump($a); // outputs int(0)

Update

In your edit you ask:

$a = new BigObject;
$b = $a; // pointer, right?
$b->updateSomethingInternally(); // $b is now changed > what about $a?

Did this trigger the copy-on-write? Or are $a and $b still identical (like in ===)?

Because $b now contains an identifier, i.e. now "points" to same object as $a, $a is also affected. There was never any copying of objects involved.