Composer as an Autoloader

In this lesson, we’ll learn about the Composer tool and how to use it as an autoloader. Composer is a dependency manager for PHP. It can download PHP libraries and attach them to your project. We’ll see how to do this in the next lesson. Composer has a feature-rich class autoloader that makes dependencies visible from our project source code. We can use it to load files from our project even if we don’t have any dependencies.

Getting started with Composer

First, we need to install Composer. The official Composer documentation explains how to do this in every operational system.

We can initialize the Composer configuration by running the php composer.phar init command in the project directory. It’ll ask several questions about the project, such as the project name and author name. We can leave default values for most of the fields. Answer no when it asks to define dependencies interactively.

Try initializing the configuration in this terminal:

After running this command, we can find a new file named composer.json in your project directory. It’s the file with the Composer configuration that looks somewhat like this:

How to configure autoloading

It’s time to tell Composer how to autoload our classes if it hasn’t been done automatically yet. We need to add the autoload field into the root object in the composer.json file.

Composer supports several autoload strategies, the primary and recommended being the PSR-4. To configure it, add a psr-4 field into the autoload project. Its value is an object with namespace prefixes as keys and base directories as values. If a single namespace prefix matches multiple base directories, we can define them as an array, for example:

We can similarly configure the PSR-0 strategy, but we typically avoid it in newer code since it’s deprecated.

If we have a directory with files that don’t match the standards, we can define it with the classmap strategy. Composer will scan this directory and add every class to the autoloader. Directory scans slow down the autoloader generation.

Also, we’ll have to regenerate the autoloader whenever we add a new class to this kind of a directory. So, it’s better to avoid the classmap strategy in the new code. At the same time, it helps work with old legacy code, for example:

If we need to include files on every instance, we can add them using the files strategy, for example:

If we need some classes only during development but not production, we can define them in the autoload-dev field instead of autoload. The configuration structure looks the same.

Generating autoloader

After configuring the autoloader, regenerate it with the command php composer.phar install. It installs missing dependencies and also generates the autoloader.

If we only want to generate the autoloader, we can do this with the command php composer.phar dump-autoload. After running one of these commands, we’ll see the new directory named vendor in the project directory. It’s a directory where Composer stores all the downloaded dependencies and generated autoloader files.

Hint: Don’t commit the vendor directory to the version control system. It will bloat the repository with many files that we didn’t make and shouldn’t edit. And, it’s useless because Composer can derive all this data from the other files in this repository. If we’re using git, this means adding the line vendor/ to the .gitignore file.

Including autoloader

There’s a autoload.php file in the vendor` directory. Include it to use the Composer autoloader.

It will probably be our project’s only require expression because we don’t have to bother with autoloading anymore.

Bringing it together

Let’s look at the same diamond-shaped application from the previous lesson. This time we use the Composer autoloader.

We could use the Greeter class without requiring the file containing it.

Conclusion

Composer has a built-in class autoloader. It’s so handy that we can use it even if we have no dependencies.

Composer supports multiple autoloading strategies. The recommended one is PSR-4. In practice, we add our source code directory into the composer.json configuration file, include the Composer autoloader, and never bother with class loading anymore.