Composer autload check for already loaded classes

Question

I'm using Composer dependency manager for php in my project. I'm building my project to off open source CMS called Concrete5. They are also loading stuffs with Composer.

Concrete5 and my own package for that uses Doctrine and Doctrine is included in both composer.json files. Do I have problem in autoloading when loading Doctrine in two different locations?

Answer 1

Composer and most other autoloaders use the standard PHP spl_register_autoload() function to keep track of the autoloading stack. This combined with the rules of PSR-0 and PSR-4 allow every registered autoloader a chance to fulfill a dependency for your code.

So when you have two autoloaders that can fulfill the same dependency, whichever one gets a chance to respond first wins. To help with this, spl_register_autoload provides a way to prepend autoloaders to the stack so that they run first. With composer this actually happens by default, the way to disable it so that the you can load the core versions of the dependency is to set prepend-autoloader to false in your package's composer.json.

{
    "prepend-autoloader": false
}

---

Another option entirely is to define provide in your packages composer.json with proper versions for the dependencies that the core provides (you can find this in concrete/composer.lock).

{
    "provide": {
        "doctrine/dbal": "v2.5.1",
        "doctrine/orm": "v2.4.8"
    }
}

This will prevent composer from pulling down duplicate versions of dependencies, the downside to this is that you'll need to keep this list up to date manually when the core updates its dependencies.