--- layout: post title: "Dependency management in PHP projects #2" date: 2013-12-08 00:25 comments: true categories: [webdev, php] cover: /images/cover/avatar.png keywords: php, composer, bundle, versions, dependencies, packages, libraries description: --- In the last [article](/2013/11/24/dependency-management-in-php-projects/) about dependency management I've explained why we, PHP programmers, need [composer](http://getcomposer.org/) and why you should use it in your PHP projects. Let's dig deeper in composer internals. # Where can I find packages for composer? Many of packages which we can use as project dependencies can be found on [packagist](https://packagist.org/). # Dependency versioning Let's say our project depends on [Twig](http://twig.sensiolabs.org/) library. The ```require``` section in ```composer.json``` file will look like this: {% codeblock lang:json %} "require": { "twig/twig": "1.12.*" } {% endcodeblock %} The file says we want Twig version at least 1.12.0. Composer will install the newest minor version (e.g. 1.12.1 or 1.12.3) of major version 1.12. We'll never get Twig 1.11 or Twig 1.13 or Twig 2.0. We can define an exact version of Twig like this: ```"twig/twig": "1.12.1"```. Maybe we want any newest development version. It's simple: ```"twig/twig": "dev-master"```. Now composer will install newest bleeding-edge version from ```master``` branch from Twig's [Git repository](https://github.com/fabpot/Twig). The used schema is: ```dev-```. # Using custom dependencies If you have your own libraries you want to use in a project, add ```repositories``` section to the ```composer.json```. It contains array of [VCS](http://en.wikipedia.org/wiki/Revision_control) repositories. Let's say you want to use a library hosted on github. Then the ```repositories``` section can look like this: {% codeblock lang:json %} "repositories": [ { "type": "git", "url": "https://github.com/vendor/example.git" } ] {% endcodeblock %} In ```type``` field we said it's a Git repository and an address of the repository is defined in ```url``` field. Then, you can edit the ```require``` section: {% codeblock lang:json %} "require": { "twig/twig": "1.12.*", "vendor/example": "dev-master" } {% endcodeblock %} Now ```composer update``` will fetch code of "example" library from ```https://github.com/vendor/example.git``` repository. # How my project knows about installed dependencies? Composer creates ```autoload.php``` file in ```vendor``` directory. The file takes care of *dynamic* autoloading of all dependencies. Dynamic means all required files are loaded when they are needed. If we had defined 20 dependencies, it would be very inefficient and slow to load all files. When some dependency class is used for the first time, composer's Autoloader gets called and tries to find and load needed files. I believe an example below enlightens the question. All you need to do is to include ```autoload.php``` file in your project. {% codeblock index.php lang:php %}