مساحات الأسماء والتحميل التلقائي

<?php
// Imagine you wrote a Logger class
class Logger {
    public function log(string $msg): void {
        echo "My log: {$msg}<br>";
    }
}

// You want to use a third-party package that also has a Logger class
// Result: PHP Fatal Error: Cannot redeclare class Logger
?>

Without namespace: Logger ← collision!
With namespace:    MyApp\Logger  vs  Vendor\Logger ← no collision!

<?php
// file: app/Utils/Logger.php
namespace App\Utils;

class Logger {
    public function log(string $msg): void {
        echo "[LOG] {$msg}<br>";
    }
}

// Use the fully qualified name
$log = new \App\Utils\Logger();
$log->log("App started");
?>

<?php
namespace App\Controllers;

// After use import, you can use the short class name
use App\Utils\Logger;
use PDO;
use DateTime;

class UserController {
    public function index(): void {
        $log = new Logger();  // No need for the fully qualified name
        $log->log("Viewing user list");
        
        $now = new DateTime();  // PHP built-in classes can also be imported
    }
}
?>

<?php
// Resolve name conflicts
use App\Models\User as AppUser;
use Vendor\Cms\User as CmsUser;

$u1 = new AppUser();
$u2 = new CmsUser();
?>

# Initialize the project
cd myphp
composer init

# Install a package (using the popular .env config library as an example)
composer require vlucas/phpdotenv

{
    "name": "myphp/demo",
    "description": "PHP Learning Project",
    "require": {
        "php": ">=8.0",
        "vlucas/phpdotenv": "^5.0"
    },
    "autoload": {
        "psr-4": {
            "App\\": "app/"
        }
    }
}

<?php
// You only need to require this one file
require __DIR__ . '/vendor/autoload.php';

// Now you can use all Composer-managed packages and your custom classes
use App\Models\User;

$user = new User();
?>

myphp/
├── app/
│   ├── Models/
│   │   └── User.php          ← namespace App\Models;
│   └── Controllers/
│       └── UserController.php ← namespace App\Controllers;
├── vendor/                   ← Created automatically by Composer
│   └── autoload.php
├── composer.json
└── public/
    └── index.php

<?php
// app/Models/User.php
namespace App\Models;

class User {
    public function __construct(
        public string $name,
        public string $email
    ) {}
}

<?php
// public/index.php
require __DIR__ . '/../vendor/autoload.php';

use App\Models\User;

$user = new User("John", "john@example.com");
echo $user->name;  // John
?>

# Install all dependencies listed in composer.json
composer install

# Add a new dependency
composer require guzzlehttp/guzzle
composer require --dev phpunit/phpunit  # Dev environment only

# Update all dependencies
composer update

# Update a specific package
composer update guzzlehttp/guzzle

# Generate optimized autoloader (production)
composer dump-autoload -o

<?php
namespace App;

// Inside a namespace, call PHP built-in classes
$date = new \DateTime();          // Root namespace \
$pdo  = new \PDO($dsn, $user, $pass);

// Or use
use DateTime, PDO;

$date = new DateTime();
$pdo  = new PDO($dsn, $user, $pass);
?>