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Handler Interface

All feature flag handlers must implement the FeatureFlagHandlerInterface, which provides a consistent way to execute code when feature flags are matched.

Interface Definition

namespace ByJG\FeatureFlag;

interface FeatureFlagHandlerInterface
{
    /**
     * Execute the feature flag handler
     *
     * @param mixed ...$args Arguments to pass to the handler
     * @return mixed The result of the handler execution
     */
    public function execute(mixed ...$args): mixed;
}

Creating a Handler

To create a custom handler, implement the FeatureFlagHandlerInterface:

use ByJG\FeatureFlag\FeatureFlagHandlerInterface;

class MyFeatureHandler implements FeatureFlagHandlerInterface
{
    public function __construct(
        private string $message
    ) {
    }

    public function execute(mixed ...$args): mixed
    {
        echo $this->message . "\n";

        // You can use the passed arguments
        if (!empty($args)) {
            echo "Arguments: " . implode(', ', $args) . "\n";
        }

        return true;
    }
}

Using the Handler

use ByJG\FeatureFlag\FeatureFlags;
use ByJG\FeatureFlag\FeatureFlagDispatcher;
use ByJG\FeatureFlag\FeatureFlagSelector;

// Define feature flags
FeatureFlags::addFlag('new-feature', 'enabled');

// Create dispatcher
$dispatcher = new FeatureFlagDispatcher();

// Add handler
$handler = new MyFeatureHandler('Feature is enabled!');
$dispatcher->add(
    FeatureFlagSelector::whenFlagIs('new-feature', 'enabled', $handler)
);

// Dispatch (with optional arguments)
$dispatcher->dispatch('arg1', 'arg2');

Handler with Dependencies

You can inject dependencies into your handlers through the constructor:

class EmailNotificationHandler implements FeatureFlagHandlerInterface
{
    public function __construct(
        private MailerInterface $mailer,
        private LoggerInterface $logger
    ) {
    }

    public function execute(mixed ...$args): mixed
    {
        $this->logger->info('Email notification feature triggered');

        $email = $args[0] ?? null;
        if ($email) {
            $this->mailer->send($email);
        }

        return null;
    }
}

// Usage with DI container
$handler = new EmailNotificationHandler($mailer, $logger);
$dispatcher->add(
    FeatureFlagSelector::whenFlagIsSet('email-notifications', $handler)
);

Stateful Handlers

Handlers can maintain state between executions:

class CounterHandler implements FeatureFlagHandlerInterface
{
    private int $count = 0;

    public function execute(mixed ...$args): mixed
    {
        $this->count++;
        echo "Handler executed {$this->count} times\n";
        return $this->count;
    }
}

:::warning Be careful with stateful handlers when the same handler instance is used across multiple dispatchers or in concurrent environments. :::

Best Practices

  1. Single Responsibility: Each handler should handle one specific feature or behavior
  2. Immutability: Prefer immutable handlers when possible
  3. Type Safety: Use proper type hints for constructor parameters
  4. Error Handling: Handle exceptions within the execute() method when appropriate
  5. Return Values: Return meaningful values that can be used for testing or chaining

See Also
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