You’ve heard of Composer, right? The nifty new tool for PHP that aims to centralize and streamline package management?

Do you also know of, but don’t really understand how namespaces work in PHP?

Then let’s set you straight! In 5 minutes you’ll learn how Composer’s autoloader and namespaces work!

Ready? Go!

Setup Composer and Download Packages

Download composer to your server:

$ curl -s https://getcomposer.org/installer | php

Create a simple composer.json file and add some packages to it. Packages can be found at packagist.org:

{
    "require": {
        "symfony/validator":         "2.1.*",
        "doctrine/dbal":             "2.2.*",
        "monolog/monolog":           "dev-master",
        "jtreminio/test-extensions": "dev-master"
    },
    "minimum-stability": "dev"
}

Run install, which will make composer setup initial environment and download requested packages:

$ ./composer.phar install

What’s Been Created

You’ll now have a composer.json, composer.lock and composer.phar file, as well as a vendor folder which contains:

vendor/composer
vendor/jtreminio
vendor/symfony
vendor/autoload.php

The vendor/autoload.php file is basically a fake loader (it calls vendor/composer/autoload_real.php – that’s about as fake as you can get!). Ignore it.

Inside vendor/bin is the PHPUnit bin (YOU’RE TESTING, RIGHT???). They were created by the phpunit/PHPUnit package that the jtreminio/test-extensions package requires. Ignore it.

The autoload_namespaces.php file

Now, open up vendor/composer/autoload_namespaces.php and you’ll see:

return array(
    'jtreminio\\TestExtensions' => $vendorDir . '/jtreminio/test-extensions/src/',
    'Symfony\\Component\\Validator' => $vendorDir . '/symfony/validator/',
    'Symfony\\Component\\Finder\\' => $vendorDir . '/symfony/finder/',
    'Monolog' => $vendorDir . '/monolog/monolog/src/',
    'Doctrine\\DBAL' => $vendorDir . '/doctrine/dbal/lib/',
    'Doctrine\\Common' => $vendorDir . '/doctrine/common/lib/',
);

These are your available namespaces. For all intents and purposes these are the namespaces your application can use (if this is the only autoloader you’re using). If the namespace is not listed in here, you can’t autoload that class.

The double backslash is for escaping purposes – composer inserts double backspaces so it won’t escape an apostrophe. It can manually be changed to a single backspace, but Don’t Do That. Never edit any files inside the vendor folder.

If you remove or add any namespaces manually, the next time you run ./composer.phar update all your changes will be thrown out the window. These namespaces are set via the composer.json file. You can also define custom namespaces, which I will show you at the end of this article.

Hurry it up!

Ok it’s been, what, 3 minutes? I guess I only have 2 minutes to explain namespaces now!

Here it is: your app’s index.php file (or whatever) needs to require the vendor/autoload.php file:

require_once __DIR__.'/vendor/autoload.php';

And now you can call any namespace identified by composer!

$foo = new \Monolog\Logger('foo');

1 minute 30 seconds!

What’s the magic?

In vendor/composer/autoload_namespaces.php:

return array(
    'jtreminio\\TestExtensions' => $vendorDir . '/jtreminio/test-extensions/src/',
    'Symfony\\Component\\Validator' => $vendorDir . '/symfony/validator/',
    'Symfony\\Component\\Finder\\' => $vendorDir . '/symfony/finder/',
    'Monolog' => $vendorDir . '/monolog/monolog/src/',
    'Doctrine\\DBAL' => $vendorDir . '/doctrine/dbal/lib/',
    'Doctrine\\Common' => $vendorDir . '/doctrine/common/lib/',
);

Looking at this specific line: 'Monolog' => $vendorDir . '/monolog/monolog/src/',

Monolog is the namespace, and $vendorDir . '/monolog/monolog/src/' is where this namespace can be found. All a namespace is in this instance is a folder name. Check your folder directory. The Logger() class is found in vendor/monolog/monolog/src/Monolog/Logger.php

vendor/monolog/monolog/src/ is the path to the namespace, Monolog is the base namespace, and Logger.php contains the Logger class.

What about the other namespaces?

// \TestExtensions\TestExtensions
PHP Code*:            $bar = new \jtreminio\TestExtensions\TestExtensions();
Namespace Identifier: 'jtreminio\\TestExtensions' => $vendorDir . '/jtreminio/test-extensions/src/',
Maps to:              vendor/jtreminio/test-extensions/src/jtreminio/TestExtensions/TestExtensions.php

// \Symfony\Component\Validator
PHP Code*:            $baz = new \Symfony\Component\Validator\Validator();
Namespace Identifier: 'Symfony\\Component\\Validator' => $vendorDir . '/symfony/validator/',
Maps to:              vendor/symfony/validator/Symfony/Component/Validator/Validator.php

Holy shit this is simple

// \Symfony\Component\Finder
PHP Code*:            $qux = new \Symfony\Component\Finder\Finder();
Namespace Identifier: 'Symfony\\Component\\Finder\\' => $vendorDir . '/symfony/finder/',
Maps to:              vendor/symfony/finder/Symfony/Component/Finder.php

// \Doctrine\DBAL
PHP Code*:            $qwe = new \Doctrine\DBAL\Connection();
Namespace Identifier: 'Doctrine\\DBAL' => $vendorDir . '/doctrine/dbal/lib/',
Maps to:              vendor/doctrine/dbal/lib/Doctrine/DBAL/Connection.php

* Won’t actually run because classes are either abstract or require constructor arguments.

Got it? Good! Because that’s 5 minutes.

Bonus Round: Custom Namespaces

So you’ve been contracted to write the next Facebook for ponies? You’re getting 10% of all future profit?! JAWESOME!

It needs a name! Let’s call it … Brony. Just roll with it.

Your app’s namespace should be Brony. It’s safe to use because I swear to God no one has had the guts to name their application Brony before you.

Open up the composer.json file and make it look like this:

{
    "require": {
        "symfony/validator":         "2.1.*",
        "doctrine/dbal":             "2.2.*",
        "monolog/monolog":           "dev-master",
        "jtreminio/test-extensions": "dev-master"
    },
    "minimum-stability": "dev",
    "autoload": {
        "psr-0": {
            "Brony":        "src/",
            "Brony\\Tests": "tests/",
        }
    }
}

Run ./composer.phar update and checkout vendor/composer/autoload_namespaces.php. You should see these two lines somewhere in that array:

    'Brony\\Tests' => $baseDir . '/tests/',
    'Brony'        => $baseDir . '/src/',

That’s it, brother. Your own custom namespace about emotionally disturbed ponies. Your final application structure would look like this:

/src/     // The "Brony" namespace
/vendor/  // Contains all composer packages
/tests/   // The "Brony/Tests" namespace
index.php // Calls the autoloader

Have fun out there!