Ok, guys: confession time. This cool little autoloader idea where we make our class name match our file name and our namespace match our directory structure ... well, that was not my idea. In fact, this idea has been around in PHP for years, and every modern project follows it. That's nice for consistency and organization, but it's also nice for a much more important reason: we can write a single autoloader function that can find anyone's code: our code or third-party code that we include in our project.

The Famous PSR-0

The idea of naming your classes and files in this way is called PSR-0. You see, there's a lovable group called the PHP FIG. It's basically the United Nations of PHP: they come together to agree on standards that everyone should follow. PSR-0 was the first standard... called 0 because we geeks start counting, well, at 0.

It simply says that Thou shalt call your class names the same as your filenames plus .php and you shall have your directory structures match up with your namespaces.

Hello Composer

Why do we care? Because instead of having to write this autoloader by hand, you can actually include an outside library that takes care of all of it for us. The library is called Jordi, I mean, Composer: you may have heard of it.

Let's get it: Go to and hit download. Copy the lines up here: if you're on Windows, you may see slightly different instructions. Then move into your terminal, open a new tab, and paste those in:

php -r "copy('', 'composer-setup.php');"
php -r "if (hash_file('SHA384', 'composer-setup.php') === 'e115a8dc7871f15d853148a7fbac7da27d6c0030b848d9b3dc09e2a0388afed865e6a3d6b3c0fad45c48e2b5fc1196ae') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;"
php composer-setup.php
php -r "unlink('composer-setup.php');"

This is downloading Composer, which is just a single, executable file. Usually people use Composer to download external libraries they want to use in their project. It's PHP's package manager.

But it has a second superpower: autoloading. When this command finishes, you'll end up with a composer.phar file. This is a PHP executable. We'll come back to it in a second.

Configuring Autoloading

To tell Composer to do the autoloading for us, all you need is a small configuration file called composer.json. Inside, add an autoload key, then a psr-4 key, and empty quotes set to lib:

7 lines composer.json
"autoload": {
"psr-4": {
"": "lib/"

That's it.

Remember how I said this rule is called PSR-0? Well PSR-4 is a slight amendment to PSR-0, but they both refer to the same thing. This tells Composer that we want to autoload using the PSR-0 convention, and that it should look for all classes inside the lib directory. That's it.

Back in your terminal, run:

php composer.phar install

This command normally downloads any external packages that we need - but we haven't defined any. But it also generates some autoload files inside a new vendor/ directory.

To use those, open bootstrap.php, delete all the manual autoload stuff, and replace it with just require __DIR__vendor/autoload.php, which is one of the files that composer just generated:

10 lines bootstrap.php
... lines 1 - 2
require __DIR__.'/vendor/autoload.php';
... lines 4 - 10

That's it.

You also usually don't commit the vendor/ directory to your Git repository: team members just run this same command when they download the project.

Let's see if it works! Go back and refresh! It does! And as we add more classes and more directories to lib/, everything will keep working. AND, if you guys want to start downloading external libraries into your project via Composer, you can do that too and immediately reference those classes without needing to worry about require statements or autoloaders. Composer takes care of everything. Thanks Jordi!

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