A short article on PHP function arguments

Everyone knows since PHP5, objects are passed by reference to the functions and methods. That mean modifying an object in a function modifies directly the data pointed by the variables.

<?php

class A
{
    public $data;
}

function modifyA(A $instance)
{
    $instance->data = 1000;
}

$a = new A();
$a->data = 0;
modifyA($a);
echo $a->data; // 1000

As the local variable $instance and $a point internally to the same data structure in memory, modifying $instance is the same as modifying $a. Adding a & front of the $instance declaration in function signature forces PHP to pass data as reference and should have exactly the same results.

Have now a look at the following code, you will understand it is not the case:

<?php

class A
{
    public $data;
}

function modifyA(A $instance)
{
    if ($instance->data === 0) {
        $instance = new A();
    }

    $instance->data = 1000;
}

$a = new A();
$a->data = 0;
modifyA($a);
echo $a->data; // 0
modifyA(&$a);
echo $a->data; // 1000

Hope that will save you some time.