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This page attempts to provide a visual guide to how objects - and references to them - work in PHP 5.0 and later.

class SimpleClass {
$var 'a default value';
$instance = new SimpleClass();
The above code creates a new class, SimpleClass, with no properties or methods.

It then creates a new instance of this class and attaches it to the variable named '$instance'.
Because objects are "special" [1] in PHP5, the relationship between the variable '$instance' and the object inside it is not as direct as you might be expecting...

$assigned = $instance; ObjRefImg1.png
For example, when we assign the variable '$instance' to a new variable '$assigned', what we end up with is the one object with two different labels.
$instance->var = '$assigned will have this value as well'; ObjRefImg3.png
Even though we changed the property via the variable '$instance', it changed the underlying object, so both '$assigned' and '$instance' will have the new value.
$reference =& $instance; ObjRefImg2.png
'$reference', on the other hand, is a reference to the variable '$instance', and is NOT attached directly to the underlying object.[citation needed]
$instance = null; ObjRefImg4.png
So when we assign NULL into '$instance', we haven't changed the object (it's still available via '$assigned'), but both '$instance' and '$reference' have lost their attachment to it.


  1. Sara Golemon, "You're Being Lied To" [1]