cannot set an index of a session

Hello. I try to change an index of a session but codeigniter sent an Error :

PHP Code:

$this->session->user['coins'] = 5; 


Code:

Indirect modification of overloaded property CI_Session::$user has no effect

But I didn't send any Error with following code:

PHP Code:

$_SESSION['user']['coins'] = 5; 


Is there any solution?

I think what you were trying to do is

PHP Code:

$this->session->user = ['coins' => 5]; 


Which produces the exact same result as

PHP Code:

$_SESSION['user']['coins'] = 5; 


After either of the above is run

PHP Code:

var_dump($_SESSION); 


produces

Code:

array (size=2)
 '__ci_last_regenerate' => int blah-blah-blah
 'user' =>
     array (size=1)
       'coins' => int 5