Taming Dependency Injection

Symfony’s DependencyInjection component is one of its most powerful features, but its complexity can feel overwhelming. In this talk, we’ll demystify the beast by exploring the core concepts, common use cases, and best practices for working with Symfony DependencyInjection.

From understanding autowiring, autoconfiguration, service containers to advanced topics like compiler passes, this talk will provide practical insights to help you harness its full potential and unlock truly SOLID code.

Transcript

1. Taming Dependency Injection @nicolasgrekas
2. @nicolasgrekas services: _defaults: autowire: true # Look at parameter types to auto-inject deps autoconfigure: true # Look at parent types to auto-register classes # Load every class in a namespace/directory as a service App\: resource: '../src/' # Add more service definitions when explicit configuration is needed config/services.yaml
3. Auto-discovery Auto-wiring Auto-configuration Three key mechanisms @nicolasgrekas
4. Auto-discovery Scan src/ for classes Register them as %FQCN% services Account for: #[When] #[WhenNot] #[Exclude] #[AsAlias] / singly-implemented interfaces @nicolasgrekas
5. Auto-wiring Figure out missing dependencies By FQCN name, not "instanceof" checks By #[Autowire] attribute @nicolasgrekas
6. @nicolasgrekas
7. Auto-configuration If it looks like a Command, make it a command @nicolasgrekas
8. @nicolasgrekas FrameworkBundle's FrameworkExtension $container->registerForAutoconfiguration(Command::class) $container->registerForAutoconfiguration(AbstractController::class) $container->registerForAutoconfiguration(FormTypeInterface::class) $container->registerForAutoconfiguration(EventSubscriberInterface::class) $container->registerForAutoconfiguration(ResetInterface::class) $container->registerForAutoconfiguration(MessageHandlerInterface::class) // ...
9. @nicolasgrekas FrameworkBundle's FrameworkExtension $container->registerAttributeForAutoconfiguration(AsEventListener::class, ...) $container->registerAttributeForAutoconfiguration(AsController::class, ...) $container->registerAttributeForAutoconfiguration(AsRemoteEventConsumer::class, ...) $container->registerAttributeForAutoconfiguration(AsMessageHandler::class, ...) $container->registerAttributeForAutoconfiguration(AsSchedule::class, ...) // ...
10. @nicolasgrekas Just Enjoy on your side #[AsEventListener] class MyRequestListener { public function __invoke(RequestEvent $event): void { // ... } }
11. @nicolasgrekas #[AutoconfigureTag] interface ChannelInterface { } Define your rules
12. @nicolasgrekas Enjoy your rules class ChannelBroadcaster { public function __construct( #[AutowireIterator(ChannelInterface::class)] iterable $channels ) { // ... }
13. @nicolasgrekas #[AsAlias(ChannelInterface::class)] class DefaultChannel implements ChannelInterface {
14. Dependency Injection #[AsDecorator] #[AsTaggedItem] #[AutowireCallable] #[AutowireDecorated] #[AutowireLocator] #[AutowireServiceClosure] #[Required] #[SubscribedService] #[Target] @nicolasgrekas
15. @nicolasgrekas #[Autoconfigure(lazy: true)] class PlotFactory { public function __construct( #[Autowire(param: 'kernel.debug')] private bool $debug, private HeavyDependency $heavyDependency, ) { } }
16. public function __construct( #[AutowireLocator([ 'router' => RouterInterface::class, 'slugger' => '?'.SluggerInterface::class, ])] ContainerInterface $container, ) @nicolasgrekas
17. @nicolasgrekas public function __construct( #[AutowireCallable(UriTemplate::class, 'expand')] UriExpanderInterface $expander, ) new class($uriTemplate->expand(...)) implements UriExpanderInterface { public function __construct( private \Closure $closure, ) { } public function expand(string $url, array $vars): string { return $this->closure->__invoke($url, $vars); } } $uriTemplate->expand(...)
18. class Vimeo { public function __construct( #[AutowireInline( factory: [ScopingHttpClient::class, 'forBaseUri'], arguments: [ '$baseUri' => 'https://api.vimeo.com', '$defaultOptions' => [ 'auth_bearer' => '%env(VIMEO_ACCESS_TOKEN)%', 'headers' => ['Accept: application/vnd.vimeo.*+json'], ] ] )] private HttpClientInterface $vimeo, ) { } @nicolasgrekas
19. $container->registerAttributeForAutoconfiguration(JsonStreamable::class, […] $definition->addExcludeTag('json_streamer.streamable', [ 'object' => $attribute->asObject, 'list' => $attribute->asList, ]); }); @nicolasgrekas
20. Context-free logic Context-aware declarations You're always in the driving seat What for? @nicolasgrekas
21. Credits @nicolasgrekas
22. Hundreds of contributors @nicolasgrekas
23. symfony.com/slack Mutual aid Kindness CARE team @nicolasgrekas
24. Thank you! @nicolasgrekas