Summary - Namespaces
- PHP course
- Advanced
- Lesson 33/92
- 5 min
Build a modular library structure with namespace, use, alias and PSR-4.
Summary - Namespaces
In this group you learned to package code with namespace, import with use, alias with as, the global namespace, and multi-level structures. Finally you wrote a PSR-4 autoloader.
Now you will combine them to build a modular library skeleton: define classes in their own namespaces and load them automatically with an autoloader.
Modular library skeleton
In a PSR-4 compliant library every class lives in its own file. The App\Services\AccountService class is defined in src/Services/AccountService.php; the caller imports it with use App\Services\AccountService;.
The autoloader loads the right file automatically. So no manual require is needed; as the project grows this matters.
Practice Use a class across multi-level namespaces
Define two namespaces with braced syntax. Inside App\Services add an AccountService class with an owner() method (returning "Alex"). Inside App\Repository, import App\Services\AccountService with use; the UserRepository class's static find(int $id): AccountService method should return new AccountService(). Get the instance with $user = UserRepository::find(42), then print the owner() output and __NAMESPACE__.
Starter code
<?php
namespace App\Services {
class AccountService {
public function owner(): string {
return "Alex";
}
}
}
namespace App\Repository {
// Import the AccountService class with use
// Add the UserRepository class and the find method
// Call find, print owner() and __NAMESPACE__
}Sample solution
<?php
namespace App\Services {
class AccountService {
public function owner(): string {
return "Alex";
}
}
}
namespace App\Repository {
use App\Services\AccountService;
class UserRepository {
public static function find(int $id): AccountService {
return new AccountService();
}
}
$user = UserRepository::find(42);
echo $user->owner() . "\n";
echo __NAMESPACE__ . "\n";
}Expected output
Alex App\Repository
Practice PSR-4 autoloader with multiple class paths
Write a classToFile(string $class): string function: strip the App\ prefix, turn the remaining \ into /, prepend src/ and append .php. Register it with spl_autoload_register. Print the file paths for both App\Models\User and App\Services\AccountService.
Starter code
<?php
// Define the classToFile function (App\ → src/)
// Register it with spl_autoload_register
// Print paths for App\Models\User and App\Services\AccountServiceSample solution
<?php
// Define the classToFile function (App\ → src/)
function classToFile(string $class): string {
$prefix = "App\\";
$base = "src/";
$relative = str_replace($prefix, "", $class);
$relative = str_replace("\\", "/", $relative);
return $base . $relative . ".php";
}
// Register it with spl_autoload_register
spl_autoload_register(function ($class) {
$file = classToFile($class);
require $file;
});
// Print paths for App\Models\User and App\Services\AccountService
echo classToFile("App\\Models\\User") . "\n";
echo classToFile("App\\Services\\AccountService") . "\n";Expected output
src/Models/User.php src/Services/AccountService.php
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Which keyword imports a class?
- import
- use Correct answer
- include
- require
Explanation: The use keyword imports a class.