Using Config helper from within config file

Is it possible to use the config() helper method within the config/app.php file its self??

I can't seem to get it to work. It just ignore it.

Example;

return [

    'extra' => 'test',

    'pages' => [
        'one',
        'two',
        'three',
        'demographics',
        'results',
        config('app.extra')
    ],

];

....from within the app.php file config('app.extra') does nothing.

via Chebli Mohamed