Composer and autoloading

What Composer does

Composer is the PHP dependency manager: it reads the composer.json file, fetches the listed packages into the vendor folder, and generates an autoloader for all of them. Fetch it from getcomposer.org and run the installer once per machine.

$json = file_get_contents(__DIR__ . "/composer.json"); $data = json_decode($json, true); echo $data["name"] ?? "no name";

PSR-4 autoloading

PSR-4 autoloading maps a namespace prefix to a folder, so the engine loads each class file on first use with no manual require per class. A tiny autoloader shows the idea: turn the class name into a path and require it when the file exists.

spl_autoload_register(function (string $class): void { $path = __DIR__ . "/src/" . $class . ".php"; if (is_file($path)) { require($path); } });

require vendor/autoload.php

Every Composer project shares one entry file that knows all installed packages and your own namespace map. Requiring it first in the front controller makes every class available to the whole request.

require(__DIR__ . "/vendor/autoload.php"); $app = new App\Kernel(); $app->run();

Your first autoloaded class

Files under src/ mirror the App namespace: the class App\Kernel lives in src/Kernel.php. After adding the map to composer.json, regenerate it once and never require the class by hand again.

namespace App; class Kernel { public function run(): void { echo "running"; } }

Next: Everyday string functions

Article author: Arthur Isaev