What is the function of "&" right before the session variable?

Question

$cart = &$_SESSION['journal_items']; anybody know when do we use the & symbol like that?

Answer 1

Basically it means that $cart won't get the value stored in $_SESSION['journal_items'], but it's reference. Whenever you call $cart, you'll be calling the current value of $_SESSION['journal_items'], even if it has been changed after this declaration.

Example:

$_SESSION['journal_items'] = "test";
$cart = &$_SESSION['journal_items'];
//$cart's current value is "test"

$_SESSION['journal_items'] = "test2";
//$cart's current value is "test2"

See this answer and this reference book.