[ref] http://symfony.com/doc/current/components/http_foundation/sessions.html

$tokens = array('tokens' => array('a' => 'a6c1e0b6',
'b' => 'f4a7b1f3'));

$tokens = $session->get('tokens');
$tokens['c'] = $value;
$session->set('tokens', $tokens);

With structured namespacing, the key can be translated to the array structure like this using a namespace character (defaults to /):

Not work with:

$session->set('tokens/c', $value);

Output

array('tokens' => array('a' => 'a6c1e0b6', b' => 'f4a7b1f3'))
and
array('tokens/c' => 'value')

Should be (?)

array('tokens' => array('a' => 'a6c1e0b6', b' => 'f4a7b1f3', 'c' => 'value'))