Composer autoloader + slim framework - 致命错误:找不到类'SlimSlim'?

How can I use composer autoloader to load slim? I have it a go below,

composer.json:

{
    "autoload": {
        "psr-4": {
            "Vendor\Namespace\": ""
        }
    }
}

index.php:

require dirname(__FILE__).'/vendor/autoload.php';

use SlimSlim;

Slim::registerAutoloader();

//Instantiate a Slim application:
$app = new Slim();

//Define a HTTP GET route:
$app->get('/', function () {
    echo "Hello!";
});

$app->get('/hello/:name/', function ($name) {
    echo "Hello, $name";
});

//Run the Slim application:
$app->run();

错误:

致命错误:在 C: 中找不到类SlimSlim"...

{
    "autoload": {
        "psr-0": {
            "": "ext/"
        }
    }
}