Dependency Injection Laravel Package

Getting Started

Minimal Setup in Laravel

1. Installation

   composer require symfony/dependency-injection
   

   Laravel already uses this under the hood (via Illuminate/Container), but standalone usage is possible.

2. First Use Case: Manual Container Initialization

   use Symfony\Component\DependencyInjection\ContainerBuilder;
   use Symfony\Component\DependencyInjection\Reference;
   
   $container = new ContainerBuilder();
   $container->register('app.service', MyService::class)
       ->setArguments([new Reference('app.other_service')]);
   
   $container->register('app.other_service', OtherService::class);
   
   $service = $container->get('app.service');
   

3. Where to Look First

   • Symfony DI Component Docs
   • Laravel’s Illuminate\Container\Container (for integration patterns)
   • ContainerBuilder and Definition classes for core functionality.

Implementation Patterns

1. Service Registration & Configuration

• Dynamic Registration

  $container->autowire(MyService::class)
      ->setPublic(true) // Expose as a service
      ->setAutowired(true); // Enable autowiring
  

• Tagging Services (for compiler passes or lazy loading)

  $definition = $container->register(MyListener::class);
  $definition->addTag('kernel.event_listener', ['event' => 'app.event']);
  

2. Integration with Laravel

• Extend Laravel’s Container

  $container = app();
  $container->extend('app.service', function ($app, $service) {
      $service->setConfig($app['config']['services']);
      return $service;
  });
  

• Replace Laravel’s Container (Advanced)

  $container = new ContainerBuilder();
  // Register Laravel bindings manually...
  $app = new LaravelApp($container);
  

3. Compiler Passes (Custom Logic)

use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
use Symfony\Component\DependencyInjection\ContainerBuilder;

class MyCompilerPass implements CompilerPassInterface {
    public function process(ContainerBuilder $container) {
        if (!$container->has('app.service')) return;
        $definition = $container->findDefinition('app.service');
        $definition->addMethodCall('setPostConfig', [['value' => 42]]);
    }
}

Register via:

$container->addCompilerPass(new MyCompilerPass());

4. Parameter Bag for Config

$container->setParameter('app.debug', env('APP_DEBUG', false));
$container->setParameter('app.services', [
    'timeout' => 30,
]);

Access in services:

$debug = $container->getParameter('app.debug');

Gotchas and Tips

Pitfalls

1. Circular Dependencies

   • Symfony DI throws CircularReferenceException. Use setLazy(true) or refactor.

   $definition->setLazy(true); // Lazy-load to break cycles
   

2. Autowiring Conflicts

   • Laravel’s autowiring may override Symfony DI’s. Explicitly register services if needed:

   $container->autowire(MyService::class)->setPublic(false);
   

3. Parameter Overrides

   • Parameters set via setParameter() replace existing ones. Use setParameterBag() for bulk updates.

4. Service Not Found

   • Check for typos in service IDs or missing setPublic(true). Use:

   $container->has('service.id'); // Verify existence
   

Debugging Tips

• Dump Container Contents

  dump($container->getServiceIds());
  dump($container->getDefinition('service.id'));
  

• Enable Debug Mode

  $container->setDebug(true); // Shows detailed errors
  

Extension Points

1. Custom Service Locators

   $container->set('app.locator', new class {
       public function find($id) { /* custom logic */ }
   });
   

2. Override Service Definitions

   $container->setDefinition('app.service', new Definition(MyService::class));
   

3. Use ContainerInterface for Read-Only Access

   $container->get('service.id'); // No modifications allowed
   

Laravel-Specific Quirks

• Avoid Mixing app() and $container Laravel’s app() is a ContainerInterface wrapper. Prefer direct $container usage for DI features.
• Priority in Service Resolution Laravel’s bindings take precedence. Use setPublic(false) to force Symfony DI resolution:

  $container->register('app.service', MyService::class)->setPublic(false);