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Composer: Part 2 - Impact

Note: This article was originally published at Planet PHP on 19 April 6060.
Planet PHP

In the first part of this post I introduced Composer & Packagist. If you are not familiar with them please read part 1 first.

Impact

In this second part I would like to talk about a few things Composer could do for you, and the PHP community at large, once it is broadly adopted.

Common APIs and Shared Interfaces

You may have noticed that quite a lot of people are talking of and asking for more interoperability and cooperation between frameworks. It seems some PHP developers finally got tired of reinventing the wheel. That is great news. One way to provide this interoperability is through shared interfaces. The two main candidates there in my opinion are logging and caching. Two boring things that should just work, and where you always need tons of flexibility and tons of different backends, drivers, or whatever you want to call those. Almost every major framework and CMS out there have their own implementations of that stuff, yet none of them support all the options since there are too many.

The PHP Standards Group, an open mailing list discussing these interoperability questions has seen a recent proposal for a Cache Interface. One question raised was: How can those interfaces be distributed in each project that uses or implements them?

This is where I see Composer helping. Composer supports advanced relationships between packages, so to solve this issue you would need three parts (read carefully):

  • The psr/cache-interface package contains the interfaces, and requires a psr/cache virtual package.
  • Implementors of the interfaces (many libraries) all require the psr/cache-interface and also provide the psr/cache virtual package.
  • A framework that needs a cache library requires psr/cache-interface and hints the interface in its method signatures.

Then the user of that framework comes in, decides that he wants to use the Doctrine\Common cache implementation for example. By requireing doctrine/common, the psr/cache requirement of the psr/cache-interface would be satisfied. Both doctrine and the framework would use the interfaces from the psr/cache-interface package. No code duplication all over the place and everyone is happier. All those require and provide have version constraints on them, so the interfaces can easily be versioned so that Composer will not let you install things that do not work together.

Plugin Installs for Frameworks and Applications

Composer is built to be embedded in other frameworks, CMSs or other applications. Some parts are still a bit rough for that use case, but it is something that will be supported and encouraged. Reinventing the package management wheel is another thing that really should stop. Who am I to say this you ask? It is true, we are building a shiny new wheel as well. Yet I take comfort in the fact that we are trying to build a generic solution which will work for everybody.

Packages are easy to build - for those who insist on not reading the first part of this post: you drop a simple composer.json file and add the VCS repository to packagist.org. The goal is that building packages should be accessible. I would love it if TYPO3, Drupal or WordPress to name a few would use Composer as a library internally to handle their dependencies. The list of required packages does not have to be in a composer.json file, it can sit in a database just fine. That would mean that suddenly the WordPress plugin you are developing could depend on an external library to do some work, and you don't have to embed the whole library code in your plugin's repository. Autoloading would make it work magically as long as everyone respects PSR-0. Which brings me to my next point.

Promoting Standards

A few months back I was on IRC and someone linked his new library, who or what it was does not matter. I just noticed he used a home-made autoloader and asked him why he was not following the PSR-0 standard. The answer was aoI just use a smarter autoloader, with fallback featureao. Now that's great, maybe his solution is smarter in the way that it allows files and classes to be anywhere. But it messes with everybody else. No one can use that library unless they declare another autoloader just for it. Autoloading should really be a commodity that you do not have to lose time fixing.

By adop

Truncated by Planet PHP, read more at the original (another 2136 bytes)