Consider the following example:
```php
<?php
$a = array("a" => 42);
$b = $a;
$b["a"] = 43;
var_dump($a);
var_dump($b);
$c=&$a;
$c["a"]=44;
var_dump($a);
var_dump($b);
var_dump($c);
```
When we say `$b=$a`, [PHP]() does **copy-on-write** so that when we say `$b["a"]=43`, [PHP]() *makes a copy of `$a`*.
If we **don't** want this to happen, we use `&` to make a reference. That is, with:
```php
<?php
$a = array("a" => 42);
$b = $a;
$b["a"] = 43;
var_dump($a);
var_dump($b);
$c=&$a;
$c["a"]=44;
var_dump($a);
var_dump($b);
var_dump($c);
```
we will see that `$c` and `$a` really do point to the same object, whereas `$b` points to its own copy of `$a`.