PHP Objects & references

• In PHP 5, objects are passing by references by default, but this statement is not completely true.
• A reference is an alias, It allows two variables to assign the same value.
• an object variable doesn't contain the object itself as value anymore.
• It only contains an object identifier that allows object accessors to find the actual object.
• When an object is sent by argument, returned or assigned to another variable, the different variables are not aliases: they hold a copy of the identifier, which points to the same object.

<?php

class A {
    public $foo = 1;
}  

$a = new A;
$b = $a;     // $a and $b are copies of the same identifier
             // ($a) = ($b) = <id>
$b->foo = 2;
echo $a->foo."\n";


$c = new A;
$d = &$c;    // $c and $d are references
             // ($c,$d) = <id>

$d->foo = 2;
echo $c->foo."\n";


$e = new A;

function foo($obj) {
    // ($obj) = ($e) = <id>
    $obj->foo = 2;
}

foo($e);
echo $e->foo."\n";


?>

Output: