Composer, Packagist & Autoloading

The problem Composer solves

So far, every time you wanted code from another file you wrote include or require by hand. On a real project that is dozens of files, and you would also need to find, download and update outside libraries (for email, PDFs, payments) manually. Composer automates all of this. It is to PHP what npm is to JavaScript — the universal dependency manager. No modern PHP project, including Laravel, works without it.

Two words to know. A dependency is outside code your project relies on (a library someone else wrote). Packagist is the giant public catalogue of PHP packages that Composer downloads from — like an app store for code.

How a Composer project works

Composer revolves around one file, composer.json, which lists what your project needs. The flow is always the same:

1. You install Composer once on your machine (from getcomposer.org).
2. In your project folder you run composer require vendor/package to add a library.
3. Composer downloads it into a vendor/ folder and records it in composer.json.
4. You add one line — require "vendor/autoload.php" — to your app, and every installed package (and your own classes) becomes available automatically.
5. Anyone else can run composer install to recreate the exact same vendor/ folder from your composer.json.

Here is installing a real, popular package — a fast unique-ID generator — from the terminal:

# in your project folder
composer require ramsey/uuid
# Composer downloads it into vendor/ and updates composer.json

Now you use that package in your code. The single require of Composer’s autoloader makes the library’s classes available with no per-file includes:

<?php
  require "vendor/autoload.php";   // the one include you still need

  use Ramsey\Uuid\Uuid;

  $id = Uuid::uuid4();
  echo "New ID: " . $id;
?>

require "vendor/autoload.php" loads Composer’s autoloader — the one and only include in a Composer project. The use line brings the Uuid class into scope (you will learn use properly in the next lesson). Uuid::uuid4() then generates a random unique identifier — code you never had to write or download manually.

Autoloading your OWN classes

Autoloading means PHP loads a class file automatically the first time you use the class — no manual require. You tell Composer where your classes live by adding an autoload section to composer.json, then run composer dump-autoload.

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

This says "any class whose name starts with App\ lives in the src/ folder". So a class App\Models\User is expected at src/Models/User.php. After adding this and running composer dump-autoload, you can use new App\Models\User() anywhere and Composer finds and loads the file for you — no require at all.