Composer and autoloading

Composer and autoloading. Composer is PHP’s dependency manager. Even if you write zero third-party packages, use it for PSR-4 autoloading so you stop hand-writing require 'models/User.php' chains.

Install Composer

Download from getcomposer.org or install via your package manager. Run composer --version to confirm it works.

composer.json basics

In your project root, create composer.json:

{
    "name": "example/my-app",
    "require": {
        "php": "^8.1"
    },
    "autoload": {
        "psr-4": {
            "App\": "src/"
        }
    }
}

The psr-4 block tells Composer: classes starting with App live under src/. Run composer install (or composer dump-autoload after changes) to generate vendor/autoload.php.

Using the autoloader

Require it once at the top of public/index.php:

<?php
declare(strict_types=1);

require dirname(__DIR__) . '/vendor/autoload.php';

use AppControllersHomeController;

$controller = new HomeController();
$controller->index();

Adding a real dependency

Need an HTTP client or a template engine? Add it with Composer rather than downloading zip files:

composer require twig/twig

Composer updates composer.json and composer.lock. Commit both. The lock file pins exact versions so another machine gets the same packages.

composer.lock and vendor/

• Commit composer.lock for applications
• Do not commit vendor/ – run composer install on deploy
• Run composer update when you intentionally want newer versions

Class example

<?php
declare(strict_types=1);

namespace AppServices;

class Greeter
{
    public function hello(string $name): string
    {
        return 'Hello, ' . Htmlspecialchars($name, ENT_QUOTES, 'UTF-8');
    }
}

File path: src/Services/Greeter.php. Namespace matches the folder structure. No manual require needed.

Composer is not Laravel-specific. WordPress plugins use it. Small scripts use it. If you outgrow a single file, reach for Composer before you invent your own autoloading.