I think your service may not be defined as an alias but as a service.. Maybe try using "alias" instead of "class" in your services.yaml ?

https://symfony.com/doc/current/service_container/alias_private.html#aliasing

Hello @smnandre ,

I changed a little the service.yaml file as you advised and I also uncomment this line App\Interface\MessageInterface $notification: '@app.message.message_second' to test the second service without the Target feature.

app.message.message_first: '@App\Service\MessageFirst'
app.message.message_second: '@App\Service\MessageSecond'

# Default used service
App\Interface\MessageInterface: '@app.message.message_first'

# Called service if we use the $notification variable (put here to compare with the Target attribute feature)
App\Interface\MessageInterface $notification: '@app.message.message_second'

App\Service\NotificationSender:
    autowire: true

In the NotificationSender class, I changed the variable for the parameter type MessageInterface to $notification to test if the second service is taking into account.

Without the Target attribute feature in the NotificationSender, everything works well. The two services are taking into account depending on commenting/uncommenting this line App\Interface\MessageInterface $notification: '@app.message.message_second' in the service.yaml.

So, our change in the services.yaml is OK. Now, I test the Target attribute feature:

First case:

Now, I suppose I comment this line in the yaml file: # App\Interface\MessageInterface $notification: '@app.message.message_second'

When I add the Target attribute in the NoficationSender class with the first service, it still doesn't work:

class NotificationSender
{
    public function __construct(
        #[Target('app.message.message_first')]
        private MessageInterface $notification
    ){
    }

    public function send(string $word): string
    {
        $sentence = $this->notification->show($word);

        return $sentence;
    }
}

I have this error:

Cannot resolve argument $notificationSender of "App\Controller\WelcomeController::showMessage()": Cannot autowire service "App\Service\NotificationSender": argument "$notification" of method "__construct()" has "#[Target('app.message.message_first')]" but no such target exists. You should maybe alias this interface to one of these existing services: "App\Service\MessageFirst", "App\Service\MessageSecond".

When I try the second service with: #[Target('app.message.message_second')], it does not work too:

Cannot resolve argument $notificationSender of "App\Controller\WelcomeController::showMessage()": Cannot autowire service "App\Service\NotificationSender": argument "$notification" of method "__construct()" has "#[Target('app.message.message_second')]" but no such target exists. You should maybe alias this interface to one of these existing services: "App\Service\MessageFirst", "App\Service\MessageSecond".

Second case:

I uncomment this line in the yaml file: App\Interface\MessageInterface $notification: '@app.message.message_second' and I test the first service with: #[Target('app.message.message_first')]. I does not work:

Cannot resolve argument $notificationSender of "App\Controller\WelcomeController::showMessage()": Cannot autowire service "App\Service\NotificationSender": argument "$notification" of method "__construct()" has "#[Target('app.message.message_first')]" but no such target exists. Did you mean to target "notification" instead?

I tested the second service with #[Target('app.message.message_second')] and it does not work too:

Cannot resolve argument $notificationSender of "App\Controller\WelcomeController::showMessage()": Cannot autowire service "App\Service\NotificationSender": argument "$notification" of method "__construct()" has "#[Target('app.message.message_second')]" but no such target exists. Did you mean to target "notification" instead?

Regards,

Try with #[Autowire(service: 'app.message.message_second')] instead of Target(...)

I tested #[Autowire(service: 'app.message.message_second')] and even #[Autowire(service: 'app.message.message_first')]. Both work well.

The #[Target] attribute doesn't work with service IDs or aliases, it expects the name of the parameter of the named alias. See https://symfony.com/blog/new-in-symfony-4-2-autowiring-by-type-and-name.

In your case, that would look something like this:

services:
    App\Interface\MessageInterface $firstMessage: '@App\Service\MessageFirst'
    App\Interface\MessageInterface $secondMessage: '@App\Service\MessageSecond'

public function __construct(
    #[Target('secondMessage')]
    private MessageInterface $message
) {
}

@HypeMC Thank you very much. Now, it works!