How to start session globally?

PHP Code:

namespace App\Controllers;
use App\Models\Modeloejemplo;
class Demo extends BaseController
{
public function __construct(){
    parent::__construct();  // <<< YOU MUST CALL THIS!! 


If calling that causes an error you must figure out why and fix it.

Regards.
That is not possible, the BaseController class does not have its own constructor, so there is no explicit constructor that can be invoked.