Containers

Delegator Factories

Expressive supports the concept of delegator factories, which allow decoration of services created by your dependency injection container, across all dependency injection containers supported by Expressive.

Delegator factories accept the following arguments:

• The container itself;
• The name of the service whose creation is being decorated;
• A callback that will produce the service being decorated.

As an example, let's say we have a UserRepository class that composes some sort of event manager. We might want to attach listeners to that event manager, but not wish to alter the basic creation logic for the repository itself. As such, we might write a delegator factory as follows:

namespace Acme;

use Psr\Container\ContainerInterface;
use Psr\Log\LoggerInterface;

class UserRepositoryListenerDelegatorFactory
{
    public function __invoke(ContainerInterface $container, string $name, callable $callback) : UserRepository
    {
        $listener = new LoggerListener($container->get(LoggerInterface::class));
        $repository = $callback();
        $repository->getEventManager()->attach($listener);
        return $repository;
    }
}

To notify the container about this delegator factory, we would add the following configuration to our application:

'dependencies' => [
    'delegators' => [
        Acme\UserRepository::class => [
            Acme\UserRepositoryListenerDelegatorFactory::class,
        ],
    ],
],

Note that you specify delegator factories using the service name being decorated as the key, with an array of delegator factories as a value. You may attach multiple delegator factories to any given service, which can be a very powerful feature.

At the time of writing, this feature works for each of the Aura.Di, Pimple, and zend-servicemanager container implementations.