Composer

Quick Introduction

Composer is a single PHP idea you'll use in almost every backend project.

In this lesson you learn only composer — not five topics at once. By the end you can write a small working example and explain it in an interview.

We connect each lesson to our course projects: Login System, Blog CMS, REST API, Inventory, Employee Management, and E-Commerce Backend.

Business Problem

You're building the REST API. After a user signs in, you need composer working correctly before storing data or showing a dashboard.

Without understanding Composer, the team ships bugs: wrong totals, broken sessions, or type errors that only appear in production. This lesson fixes that with one clear pattern you can copy into your project today.

Core Concept

• Composer is one focused idea — learn it before mixing with other PHP topics.
• Use it in PHP 8.3+ with declare(strict_types=1); at the top of every file.
• Our course project (REST API) uses composer in real handlers.
• Run small scripts with php file.php after each change — don't just read.
• Interviewers ask for a one-minute explanation plus a tiny code sample.

Syntax

Core syntax for Composer. Every keyword below appears in production PHP — Laravel and Symfony use the same primitives under the hood.

declare(strict_types=1);

Keywords: declare · strict_types · namespace

Step-by-Step Example

Run this script locally. Change one value, run again, and watch what changes.

<?php
declare(strict_types=1);

// composer.json structure (install with: composer install)
/*
{
  "name": "acme/shop-api",
  "require": { "php": "^8.3", "monolog/monolog": "^3.0" },
  "autoload": { "psr-4": { "Acme\\Shop\\": "src/" } },
  "scripts": { "test": "phpunit" }
}
*/

require __DIR__ . '/vendor/autoload.php';

use Monolog\Logger;
use Monolog\Handler\StreamHandler;

$log = new Logger('shop');
$log->pushHandler(new StreamHandler('php://stderr', Logger::INFO));
$log->info('Composer autoload ready', ['php' => PHP_VERSION]);

Line by line

1. — part of the composer example; run the file to see the result.
2. declare(strict_types=1); — turns on strict type checking for this file.
3. /* — part of the composer example; run the file to see the result.
4. { — part of the composer example; run the file to see the result.
5. "name": "acme/shop-api", — part of the composer example; run the file to see the result.

Composer OK

Real-World Example

In the REST API, composer appears in a single request handler — not spread across ten files. Keep the example small, test it with php, then paste the pattern into your project branch.

<?php
declare(strict_types=1);

// TODO: Composer exercise for REST API