Get service via class name from iterable - injected tagged services

Question

I am struggling to get a specific service via class name from group of injected tagged services.

Here is an example: I tag all the services that implement DriverInterface as app.driver and bind it to the $drivers variable.

In some other service I need to get all those drivers that are tagged app.driver and instantiate and use only few of them. But what drivers will be needed is dynamic.

services.yml

_defaults:
        autowire: true
        autoconfigure: true
        public: false
        bind:
            $drivers: [!tagged app.driver]

_instanceof:
        DriverInterface:
            tags: ['app.driver']

Some other service:

/**
 * @var iterable
 */
private $drivers;

/**
 * @param iterable $drivers
 */
public function __construct(iterable $drivers) 
{
    $this->drivers = $drivers;
}

public function getDriverByClassName(string $className): DriverInterface
{
    ????????
}

So services that implements DriverInterface are injected to $this->drivers param as iterable result. I can only foreach through them, but then all services will be instantiated.

Is there some other way to inject those services to get a specific service via class name from them without instantiating others?

I know there is a possibility to make those drivers public and use container instead, but I would like to avoid injecting container into services if it's possible to do it some other way.

Answer 1

A ServiceLocator will allow accessing a service by name without instantiating the rest of them. It does take a compiler pass but it's not too hard to setup.

use Symfony\Component\DependencyInjection\ServiceLocator;
class DriverLocator extends ServiceLocator
{
    // Leave empty
}
# Some Service
public function __construct(DriverLocator $driverLocator) 
{
    $this->driverLocator = $driverLocator;
}

public function getDriverByClassName(string $className): DriverInterface
{
    return $this->driverLocator->get($fullyQualifiedClassName);
}

Now comes the magic:

# src/Kernel.php
# Make your kernel a compiler pass
use Symfony\Component\DependencyInjection\Compiler\CompilerPassInterface;
class Kernel extends BaseKernel implements CompilerPassInterface {
...
# Dynamically add all drivers to the locator using a compiler pass
public function process(ContainerBuilder $container)
{
    $driverIds = [];
    foreach ($container->findTaggedServiceIds('app.driver') as $id => $tags) {
        $driverIds[$id] = new Reference($id);
    }
    $driverLocator = $container->getDefinition(DriverLocator::class);
    $driverLocator->setArguments([$driverIds]);
}

And presto. It should work assuming you fix any syntax errors or typos I may have introduced.

And for extra credit, you can auto register your driver classes and get rid of that instanceof entry in your services file.

# Kernel.php
protected function build(ContainerBuilder $container)
{
    $container->registerForAutoconfiguration(DriverInterface::class)
        ->addTag('app.driver');
}