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Defining namespaces

PHP course · Advanced · Lesson 27/92

Learn to package code with the namespace keyword.

What is namespace for?

In some projects same-named classes clash: two libraries may both define User. namespace solves this; it sorts classes into packages. When you write namespace App;, the User class actually carries the name App\User.

The declaration goes right after the PHP opening tag, as the first statement in the file. Every class, function and constant below joins this namespace. Use \ to separate levels: App\Models\User.

How do you write a namespace declaration?

When you write namespace App\Models; in a file, PHP places every class in that file under the App\Models package. Before the declaration only the PHP opening tag and a declare statement may appear; no other code.

The __NAMESPACE__ constant returns the current namespace name as a string. This is useful when debugging or building class names dynamically.

Exercise Define a namespace and a class

Define namespace App\Utils;. Add a Helper class with public static function greet($name) that prints the name with a "Hello, " prefix. Then call Helper::greet("Alex") and print __NAMESPACE__.

Show example solution 
:greet("Alex"); and echo __NAMESPACE__ . "\n".
Example solution:
<?php
namespace App\Utils;

class Helper {
    public static function greet($name) {
        echo "Hello, " . $name . "!\n";
    }
}

Helper::greet("Alex");
echo __NAMESPACE__ . "\n";

Test yourself

  1. What does namespace do?

    • It runs code faster
    • It prevents same-name class collisions
    • It manages database connections
    • It provides automatic error handling
    Show answer

    It prevents same-name class collisions — Correct. namespace sorts same-named classes into different packages.

  2. Complete the namespace declaration

    <?php
____ App\Services\UserService;

class UserService {
    public array $info = ["name" => "default"];
}
    Show answer 
    <?php
namespace App\Services\UserService;

class UserService {
    public array $info = ["name" => "default"];
}

  3. Match the namespace concepts

    namespace
    Packages code
    __NAMESPACE__
    Gives current name
    \
    Level separator
    ;
    Ends the declaration

All lessons in Advanced

1 PDO basics

  1. What is PDO?
  2. Connecting with PDO
  3. Running queries with query()
  4. Single row with fetch()
  5. All rows with fetchAll()
  6. Fetch mode constants
  7. Summary - PDO basics

2 Prepared statements

  1. Prepared statements with prepare()
  2. Running with execute()
  3. Binding parameters with bindParam()
  4. Binding values with bindValue()
  5. SQL injection and prevention
  6. Named placeholders
  7. Summary - Prepared statements

3 CRUD operations

  1. Inserting records with INSERT
  2. Reading records with SELECT
  3. Updating records with UPDATE
  4. Deleting records with DELETE
  5. Affected rows with rowCount()
  6. Transaction management
  7. Summary - CRUD operations

4 Project: Blog with PDO

  1. Project: Blog with PDO
  2. Database structure
  3. Adding and listing posts
  4. Editing and deleting posts
  5. Project final - Blog with PDO

5 Namespaces

  1. Defining namespaces
  2. Importing with use
  3. Aliases
  4. Global namespace
  5. Multi-level namespaces
  6. PSR-4 autoloading
  7. Summary - Namespaces

6 Composer

  1. What is Composer?
  2. The composer.json file
  3. Adding packages with require
  4. Autoload (PSR-4)
  5. Installing packages from Packagist
  6. composer update and install
  7. Summary - Composer

7 Regex

  1. Matching with preg_match()
  2. Replacing with preg_replace()
  3. All matches with preg_match_all()
  4. Character classes
  5. Quantifiers
  6. Capture groups
  7. Summary - Regex

8 JSON and API

  1. Encoding with json_encode()
  2. Parsing with json_decode()
  3. JSON error handling
  4. Content-Type with header()
  5. REST API basics
  6. HTTP methods
  7. Summary - JSON and API

9 Project: REST API

  1. Project: REST API
  2. Routing structure
  3. CRUD endpoints
  4. JSON response format
  5. Project final - REST API

10 Security

  1. Hashing with password_hash()
  2. Verifying with password_verify()
  3. SQL injection prevention
  4. XSS prevention
  5. CSRF token generation
  6. Security headers
  7. Summary - Security

11 Middleware

  1. The middleware pattern
  2. Request/Response cycle
  3. Middleware chain
  4. Auth middleware
  5. Logging middleware
  6. PSR-15 basics
  7. Summary - Middleware

12 Testing basics

  1. What is PHPUnit?
  2. Writing your first test
  3. Assertions
  4. Test layout (AAA)
  5. Test doubles (mock, stub)
  6. setUp and tearDown
  7. Summary - Testing basics

13 Design patterns

  1. The Singleton pattern
  2. The Factory pattern
  3. The Observer pattern
  4. The Strategy pattern
  5. The Decorator pattern
  6. The Adapter pattern
  7. Summary - Design patterns

14 Advanced final

  1. Challenge - PDO and API
  2. Challenge - Security app
  3. Challenge - Design patterns
  4. Challenge - Writing tests
  5. Challenge - Mini framework