如何在Silex中加载定义文件？

Question

I'm new to silex, and I've got a file that creates a few defines. This is its content:

<?php 

namespace Config;

define('DS',DIRECTORY_SEPARATOR); 
define('ROOT',realpath(__DIR__ . '/../..')); 
define('CONFIG',ROOT.DS.'app'.DS.'config');

I'm trying to load it using my composer.json:

{
    "require": {
        "silex/silex": "~2.0",
        "twig/twig": "^1.33",
        "doctrine/dbal": "^2.5",
        "symfony/twig-bridge": "^3.2",
        "boxedcode/silex-knp-menu-service-provider": "^1.0",
        "symfony/form": "^3.2",
        "symfony/validator": "^3.2",
        "symfony/config": "^3.2"
    },
    "autoload": {
        "psr-4": {
            "Models\\": "src/MyApp/Models/",
            "Config\\": "src/MyApp/Config/"
        }
    }
}

The defines file is inside src/MyApp/Config/, so I therefore hoped this line would be enough to load the defines file in my index.php file:

use Config\Defines;

But... it seems not... Can anyone tell me how to load the defines file so that I can use my Config class again?