Composer

What Composer Is

Composer is PHP’s dependency manager. It installs libraries, generates autoload files, and makes your project compatible with the modern PHP ecosystem.

Initialize a Project

In a real project, you start with composer init or create composer.json.

composer init

Install a Package

Composer downloads dependencies into vendor/ and updates composer.lock for reproducible installs.

composer require vlucas/phpdotenv

Autoloading

Composer generates an autoloader. You include it once, then your classes load automatically.

<?php
require __DIR__ . "/../vendor/autoload.php";

PSR-4 Autoload Example

Map namespaces to folders in composer.json.

{
  "autoload": {
    "psr-4": {
      "App\\": "src/"
    }
  }
}

Production Tip

Commit composer.lock. Run composer install --no-dev --optimize-autoloader in production builds.