PHP Sub Variables

PHP Sub Variables

Im currently using session variables to store a users information but i
want to change it for ease of coding to variables like $user->username
Variable im using:
$_SESSION['username']
$_SESSION['email']
$_SESSION['firstname']
$_SESSION['lastname']
$_SESSION['ip']
$_SESSION['level']
$_SESSION['subscriber']
Variables i want to use:
$user->username
$user->email
$user->firstname
$user->lastname
$user->ip
$user->level
$user->subscriber