Composer psr-0 autoloading of custom namespaces does not work

Question

I have trouble adding my own namespaces to composer with PSR-0. I have read this and this but I still can't make it work

composer.json

{
"require": {
    "klein/klein": "2.0.x",
    "doctrine/orm": "2.4.4"

},
"autoload": {
    "psr-0": {
        "mynamespace":        "src/"
        }
}
}

The src folder is placed inside the same directory as composer.json

The src directory has the following structure

src
└── mynamespace
    ├── Keys.php

Keys.php

<?php
namespace mynamespace\Keys;

define ("API_KEY", "XXXXXXXXXXXX");
?>

index.php

use Klein\Klein;
use mynamespace\Keys;
require_once __DIR__ . '/vendor/autoload.php';

$klein = new Klein(); // works
echo API_KEY;  // Undefined constant

Answer 1

You can only load classes, interfaces and traits with autoloading.

Because all you do is add a use clause which does not do anything by itself with autoloading (i.e. it does not load something), and you do not use a class, nothing happens.

I recommend using class constants. They may be put into classes or interfaces:

namespace mynamespace;

interface Keys {
    const API_KEY = 'XXXXXXXX';
}

use mynamespace/Keys;
echo Keys::API_KEY;