Composer autoload mechanism in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Composer autoload usage?

Given the following PHP code that uses Composer's autoload, what will be the output?

require 'vendor/autoload.php';

use App\Utils\Greeting;

$greet = new Greeting();
echo $greet->sayHello();

Assume the class App\Utils\Greeting is correctly defined in src/Utils/Greeting.php and Composer's autoload is configured with PSR-4 for the App\ namespace.

PHP

require 'vendor/autoload.php';

use App\Utils\Greeting;

$greet = new Greeting();
echo $greet->sayHello();

A Fatal error: Class 'App\Utils\Greeting' not found

B Hello from Greeting!

C Warning: require(vendor/autoload.php): failed to open stream

D Parse error: syntax error, unexpected 'use' (T_USE)

💡 Hint

Think about how Composer's autoload maps namespaces to file paths.

Composer's autoload uses PSR-4 to map the App\ namespace to the src/ directory. The class Greeting is found and loaded automatically, so the method sayHello() runs and outputs the greeting.

🧠 Conceptual

intermediate

Which file does Composer generate for autoloading classes?

Composer generates a file that handles autoloading of classes based on your composer.json configuration. What is the name and location of this file?

A composer/autoload.php

B autoload.php in the project root

C src/autoload.php

D vendor/autoload.php

💡 Hint

Look inside the vendor directory after running composer install.

The file vendor/autoload.php is generated by Composer and is the main entry point to autoload all classes according to the configured autoload rules.

🔧 Debug

advanced

Why does this Composer autoload fail to load the class?

Consider this composer.json snippet:

{
  "autoload": {
    "psr-4": {
      "App\\": "src/"
    }
  }
}

And this PHP code:

require 'vendor/autoload.php';

use App\Controllers\HomeController;

$controller = new HomeController();

The file src/Controllers/HomeController.php exists and defines the class App\Controllers\HomeController. However, running the code causes a Class not found error. What is the most likely cause?

A The require statement path is wrong and does not include autoload.php

B The namespace in HomeController.php is incorrect and does not match App\Controllers

C Composer's autoload files were not regenerated after adding the class file

D The class HomeController is declared as abstract and cannot be instantiated

💡 Hint

Think about what Composer needs to do after adding new classes.

Composer generates autoload files when you run composer dump-autoload or composer install. If you add new class files without regenerating, the autoloader won't know about them, causing a class not found error.

📝 Syntax

advanced

What error does this Composer autoload code produce?

What error will this PHP code produce?

require 'vendor/autoload.php'

use App\Models\User;

$user = new User();

A Parse error: syntax error, unexpected 'use' (T_USE)

B Fatal error: Class 'App\Models\User' not found

C Warning: require(vendor/autoload.php): failed to open stream

D No error, outputs nothing

💡 Hint

Check the syntax carefully, especially punctuation.

The missing semicolon after the require statement causes a parse error at the next line where 'use' is found.

🚀 Application

expert

How many classes will be autoloaded with this Composer config?

Given this composer.json autoload section:

{
  "autoload": {
    "psr-4": {
      "Lib\\": "lib/",
      "Lib\\Utils\\": "lib/Utils/"
    }
  }
}

And the following files exist:

• lib/Helper.php (class Lib\Helper)
• lib/Utils/Parser.php (class Lib\Utils\Parser)
• lib/Utils/Formatter.php (class Lib\Utils\Formatter)
• lib/Utils/Extra/Tool.php (class Lib\Utils\Extra\Tool)

How many of these classes will be autoloaded correctly by Composer?

A 4

B 1

C 3

D 2

💡 Hint

Remember how PSR-4 prefixes work and how they map to directories.

The prefix "Lib\\": "lib/" maps Lib\Helper to lib/Helper.php. The prefix "Lib\\Utils\\": "lib/Utils/" maps Lib\Utils\Parser to lib/Utils/Parser.php, Lib\Utils\Formatter to lib/Utils/Formatter.php, and Lib\Utils\Extra\Tool to lib/Utils/Extra/Tool.php because PSR-4 supports mapping the remaining namespace components to subdirectories. Thus, all 4 classes will be autoloaded correctly.