Ahnii!

Remember PHP's manual require days? Last week, I helped a team upgrade their legacy app – over 50 require statements per file! Let's see how PSR-4 autoloading solves this.

Understanding PSR-4 (5 minutes)

PSR-4 is your code's automatic file locator. Like a GPS using addresses, PSR-4 uses namespaces to find classes.

Key Concepts (2 minutes)

1. Fully Qualified Class Name (FQCN): Vendor\Package\Class. Think of it as the complete address of your class.
2. Directory Structure: A well-organized project directory with namespace-to-directory mappings.

Real-World Example (10 minutes)

Project structure:

vendor/
└── jonesrussell/
    └── blog/
        ├── composer.json
        └── src/
            └── Post/
                ├── PostController.php
                └── PostRepository.php

Setting Up Composer (3 minutes)

composer.json:

{
    "name": "jonesrussell/blog",
    "autoload": {
        "psr-4": {
            "JonesRussell\\Blog\\": "src/"
        }
    }
}

Creating Classes (2 minutes)

PostController.php:

 'Ready to blog!'];
    }
}

Common Patterns (5 minutes)

Multiple Namespace Roots:

{
    "autoload": {
        "psr-4": {
            "JonesRussell\\Blog\\": "src/",
            "JonesRussell\\Blog\\Tests\\": "tests/"
        }
    }
}

Nested Namespaces: (File location: src/Core/Database/Connection.php)

config = $config;
    }
}

Framework Examples (5 minutes)

Laravel and Symfony use PSR-4 by default.

Laravel Example:

Symfony Example:

render('blog/index.html.twig');
    }
}

Troubleshooting (3 minutes)

• "Class Not Found" Errors: Run composer dump-autoload.
• Directory Structure Issues: Ensure your directory structure matches your namespaces (case-sensitive!).

Testing (2 minutes)

Create test-autoload.php:

index()); // Should output "Ready to blog!"

Next Steps

Next, we'll cover PSR-6 (caching). This is part of our PSR Standards series.

Resources

• Official PSR-4 Specification
• Composer Autoloading Documentation
• Series Example Repository (v0.3.0 - PSR-4 Implementation)