PHP Decorators

DecoratorInterface.php

<?php

declare(strict_types=1);

interface DecoratorInterface
{
    public static function handle(\Reflector $context, self $instance): void;
}

example.php

<?php

require __DIR__ . '/vendor/autoload.php';

new StructureExample();

// TypeError@anonymous: The structure class does not allow method StructureExample::method() to be declared in example\StructureExample.php:20
// Stack trace:
// #0 example\PhpStruct.php(31): PhpStruct->error(Object(ReflectionMethod))
// #1 example\PhpStruct.php(65): PhpStruct->assert(Object(ReflectionClass))
// #2 example\interceptor.php(36): PhpStruct::handle(Object(ReflectionClass), Object(PhpStruct))
// #3 example\example.php(11): {closure}('StructureExample')
// #4 {main}

interceptor.php

<?php

declare(strict_types=1);

use Composer\Autoload\ClassLoader;

$composer = (static function (): ClassLoader {
    $trace = debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS) ?? [];

    while ($trace) {
        $current = array_shift($trace);

        if (str_starts_with($current['class'] ?? '', 'ComposerAutoloaderInit')) {
            return $current['class']::getLoader();
        }
    }

    throw new LogicException('File ' . __FILE__ . ' MUST be loaded though composer');
})();

spl_autoload_register(static function (string $class) use ($composer) {
    $composer->loadClass($class);

    if (\class_exists($class, false)) {
        $reflection = new \ReflectionClass($class);

        foreach ($reflection->getAttributes(DecoratorInterface::class, \ReflectionAttribute::IS_INSTANCEOF) as $context) {
            ($context->getName())::handle($reflection, $context->newInstance());
        }

        foreach ($reflection->getProperties() as $property) {
            foreach ($property->getAttributes(DecoratorInterface::class, \ReflectionAttribute::IS_INSTANCEOF) as $context) {
                ($context->getName())::handle($property, $context->newInstance());
            }
        }

        foreach ($reflection->getMethods() as $method) {
            foreach ($method->getAttributes(DecoratorInterface::class, \ReflectionAttribute::IS_INSTANCEOF) as $context) {
                ($context->getName())::handle($method, $context->newInstance());
            }
        }
    }
}, true, true);

PhpStruct.php

<?php

declare(strict_types=1);

#[\Attribute]
class PhpStruct implements DecoratorInterface
{
    private const ERROR_METHOD = 'The structure class does not allow method %s::%s() to be declared';

    private function assert(\ReflectionClass $class): bool
    {
        foreach ($class->getMethods() as $method) {
            throw $this->error($method);
        }

        return true;
    }

    private function error(\ReflectionMethod $method): \TypeError
    {
        $message = \sprintf(self::ERROR_METHOD, $method->getDeclaringClass()->getName(), $method->getName());

        return new class($message, $method) extends \TypeError {
            public function __construct(string $message, \ReflectionMethod $ctx)
            {
                parent::__construct($message);

                $this->file = $ctx->getFileName();
                $this->line = $ctx->getStartLine();
            }
        };
    }

    public static function handle(\Reflector $context, DecoratorInterface $instance): void
    {
        assert($instance instanceof self);

        $instance->assert($context);
    }
}

StructureExample.php

<?php

declare(strict_types=1);

#[PhpStruct]
class StructureExample
{
    public string $field;

    // Struct (data-class) can not contain methods
    public function method()
    {
    }
}