Explain PHP 8+ Attributes with a practical example. How do they differ from annotations and what are their performance implications?

PHP Attributes (PHP 8.0+):

Practical Example - API Route Mapping:

#[Attribute(Attribute::TARGET_METHOD)]
class Route {
    public function __construct(
        public string $method,
        public string $path,
        public array $middleware = []
    ) {}
}

#[Attribute(Attribute::TARGET_PARAMETER)]
class Validate {
    public function __construct(public string $rules) {}
}

class UserController {
    #[Route("POST", "/users", ["auth", "throttle"])]
    public function create(
        #[Validate("required|email")] string $email,
        #[Validate("required|min:8")] string $password
    ): User {
        return User::create(compact("email", "password"));
    }
}

// Attribute Processing
class RouteProcessor {
    public function processController(string $className): array {
        $reflection = new ReflectionClass($className);
        $routes = [];
        
        foreach($reflection->getMethods() as $method) {
            $attributes = $method->getAttributes(Route::class);
            foreach($attributes as $attribute) {
                $route = $attribute->newInstance();
                $routes[] = [
                    "method" => $route->method,
                    "path" => $route->path,
                    "handler" => [$className, $method->getName()],
                    "middleware" => $route->middleware
                ];
            }
        }
        return $routes;
    }
}

Differences from Annotations:

• Native Support: Built into PHP, no parsing needed
• Type Safety: Attributes are actual PHP classes
• Performance: Compiled into opcache, faster than docblock parsing
• IDE Support: Full autocompletion and refactoring

Performance Implications:

• Compile Time: Minimal overhead, cached in opcache
• Runtime: Only accessed via Reflection API when needed
• Memory: Stored efficiently in opcache metadata