PHP Namespaces

Why Use Namespaces?

🔹 Basic Namespace Declaration

Namespaces are declared at the beginning of a PHP file using the namespace keyword. They must be the first statement in the file, before any other code.

<?php
namespace App\Controllers;

class HomeController {
    public function index() {
        return "Welcome to Home Page";
    }
}

// Using the class in the same namespace
$controller = new HomeController();
echo $controller->index();
?>

🔹 Using Classes from Different Namespaces

To use a class from a different namespace, you can either use the fully qualified name or import it with the use keyword for cleaner code.

<?php
namespace App\Models;

class Product {
    public $name = "Laptop";
}

namespace App\Controllers;

// Method 1: Fully qualified name
$product1 = new \App\Models\Product();
echo $product1->name . "<br>";

// Method 2: Using 'use' statement
use App\Models\Product;

$product2 = new Product();
echo $product2->name;
?>

🔹 Sub-namespaces

Namespaces can be nested to create a hierarchical structure, similar to folders and subfolders, helping you organize complex applications more effectively.

<?php
namespace App\Database\Models;

class User {
    public $role = "admin";
}

namespace App\Database\Controllers;

class UserController {
    public function getUser() {
        // Access class from sibling namespace
        $user = new \App\Database\Models\User();
        return "User role: " . $user->role;
    }
}

$controller = new UserController();
echo $controller->getUser();
?>

🔹 The 'use' Keyword

The use keyword imports classes, functions, or constants from other namespaces, making your code cleaner and easier to read by avoiding long fully qualified names.

<?php
namespace App\Services;

class EmailService {
    public function send() {
        return "Email sent";
    }
}

class SmsService {
    public function send() {
        return "SMS sent";
    }
}

namespace App;

use App\Services\EmailService;
use App\Services\SmsService;

$email = new EmailService();
$sms = new SmsService();

echo $email->send() . "<br>";
echo $sms->send();
?>

🔹 Aliasing with 'as'

When importing classes with the same name from different namespaces, use the as keyword to create aliases and avoid naming conflicts in your code.

<?php
namespace App\Models;

class User {
    public $type = "App User";
}

namespace Admin\Models;

class User {
    public $type = "Admin User";
}

namespace App;

use App\Models\User as AppUser;
use Admin\Models\User as AdminUser;

$appUser = new AppUser();
$adminUser = new AdminUser();

echo $appUser->type . "<br>";
echo $adminUser->type;
?>

🔹 Global Namespace

Classes without a namespace declaration belong to the global namespace. Use a backslash prefix to access global classes from within a namespace.

<?php
// Global namespace
class GlobalClass {
    public $name = "I'm global";
}

namespace App;

class LocalClass {
    public $name = "I'm local";
}

// Access global class with backslash
$global = new \GlobalClass();
$local = new LocalClass();

echo $global->name . "<br>";
echo $local->name;
?>

🔹 Namespace Constants and Functions

Namespaces can contain not only classes but also functions and constants, allowing you to organize all types of code elements logically.

<?php
namespace App\Helpers;

const APP_VERSION = "1.0.0";

function formatDate($date) {
    return date("Y-m-d", strtotime($date));
}

namespace App;

use function App\Helpers\formatDate;
use const App\Helpers\APP_VERSION;

echo "Version: " . APP_VERSION . "<br>";
echo "Date: " . formatDate("2025-10-14");
?>

🔹 Practical Example: MVC Structure

Namespaces are essential in modern PHP applications, especially when following the MVC pattern. They help organize controllers, models, and views into logical groups.

<?php
namespace App\Models;

class Article {
    public $title = "PHP Namespaces";
}

namespace App\Controllers;

use App\Models\Article;

class ArticleController {
    public function show() {
        $article = new Article();
        return "Showing: " . $article->title;
    }
}

namespace App\Views;

use App\Controllers\ArticleController;

class ArticleView {
    public function render() {
        $controller = new ArticleController();
        return $controller->show();
    }
}

$view = new ArticleView();
echo $view->render();
?>

🔹 Namespace Best Practices

🔹 Autoloading with Namespaces

Namespaces work perfectly with autoloading, allowing PHP to automatically load class files when needed. This is the foundation of modern PHP development with Composer.

<?php
// composer.json autoload configuration
{
    "autoload": {
        "psr-4": {
            "App\\": "src/"
        }
    }
}

// File: src/Models/User.php
namespace App\Models;

class User {
    public $name = "Auto-loaded User";
}

// File: index.php
require 'vendor/autoload.php';

use App\Models\User;

$user = new User();
echo $user->name;
?>