Steps to set up a Modules directory in CI 4

 To add a modules directory in CodeIgniter 4, you need to create the directory in your project's root and configure the autoloader to recognize a new namespace for it. This allows you to organize application components into modular, self-contained units. 

Steps to set up a Modules directory

1. Create the Modules directory: In your project's root directory (alongside the app, public, and system folders), create a new folder named Modules (or modules, but capitalization must be consistent).
2. Configure Autoloading: Open the app/Config/Autoload.php file and add the Modules namespace to the $psr4 array.
   php

   // In app/Config/Autoload.php
   
   public $psr4 = [
       APP_NAMESPACE => APPPATH, // For custom namespace
       'App'         => APPPATH, // To ensure filters, etc still found,
       'Config'      => APPPATH . 'Config',
       'Modules'     => ROOTPATH . 'Modules', // Add this line
   ];
   

   Note: ROOTPATH refers to your project's root directory.
3. Create a sample module structure: Inside the Modules folder, create a directory for your specific module (e.g., Blog). Inside the Blog module folder, you can mirror the structure of the main app folder with its own Controllers, Models, Views, Config, etc..Example structure:

   /
   ├── app/
   ├── public/
   ├── system/
   ├── Modules/
   │   ├── Blog/
   │   │   ├── Config/
   │   │   ├── Controllers/
   │   │   │   └── Blog.php
   │   │   ├── Models/
   │   │   └── Views/
   ...
   

4. Define a Controller with the correct namespace: In your module's controller file (e.g., Modules/Blog/Controllers/Blog.php), ensure the namespace matches your configuration.
   php

   <?php namespace Modules\Blog\Controllers;
   
   use App\Controllers\BaseController;
   
   class Blog extends BaseController
   {
       public function index()
       {
           echo 'Hello from the Blog Module!';
       }
   }
   

5. Set up Routing: You can define routes for your module in app/Config/Routes.php or create a separate routes file within the module itself that is automatically discovered. To use module-level routes, you must ensure the main application's route file is set to discover them, and define the routes with the full namespace in the module's Config/Routes.php file.For a simple route in app/Config/Routes.php to the example above:
   php

   $routes->get('/blog', 'Modules\Blog\Controllers\Blog::index');
   

    

For detailed official documentation on Code Modules and auto-discovery, refer to the CodeIgniter User Guide