Unpack Symfony "tagged Services" - symfony

Question

I got a class which accepts multiple Consumer implementations as constructor arguments.
I want to "fill in" all my Consumers via the Symfony DI-Container.
I tried injection tagged services.
final class SynchronousMessageDispatcher implements MessageDispatcher
{
/**
* #var Consumer[]
*/
private $consumers;
public function __construct(Consumer ...$consumers)
{
$this->consumers = $consumers;
}
}
So I tried to Tag the services in the services.yml like that:
services:
_instanceof:
EventSauce\EventSourcing\Consumer:
tags: ['eventsauce.consumer']
And then inject it like this:
eventsauce.message_dispatcher:
class: EventSauce\EventSourcing\SynchronousMessageDispatcher
arguments: [!tagged eventsauce.consumer]
Now I'm getting the following error:
Argument 1 passed to EventSauce\EventSourcing\SynchronousMessageDispatcher::__construct() must implement interface EventSauce\EventSourcing\Consumer, instance of Symfony\Component\DependencyInjection\Argument\RewindableGenerator given
I fully understand why. Is there a way to unpack services
In other words: Is it possible to modify [!tagged eventsauce.consumer] somehow. Or is the ...$consumers syntax incompatible with the Tagged service Injection in Symfony.
Don't get me wrong. I know that I can easily implement MessageDispatcher myself. Just wanted to know ;-)

Answer 1

My original solution:
As "Tomáš Votruba" mentioned you'd have to rewrite your own !tagged functionality. e.g. !tagged-variadic.
This is not worth the effort for me. I'd rather implement the class using an iteratable ("nifr" explained the benefits, thanks).
For further reading, there is a closed issue on symfony/symfony#23608
My new solution
I used Argument unpacking and the Delegation pattern to use the class the library provided with my tagged services.
Work :-) Hurray.
final class TaggedMessageDispatcher implements MessageDispatcher {
public function __construct(iterable $consumers)
{
$this->dispatcher = new SynchronousMessageDispatcher(... $consumers);
}
public function dispatch(Message ...$messages): void
{
$this->dispatcher->dispatch(... $messages);
}
}

Answer 2

You're using a wrong typehint here.
With the [!tagged <tag>] syntax a single iterable will be injected - not an undefined number of arguments as expected by the splat operator.
You're actually typehinting for multiple Consumer objects as arguments with the splat (...$arguments) operator here.
So the answer to your question is:
The splat operator is not compatible with the [!tagged ..] syntax.
You'd indeed need to write your own injection type that splits up the tagged services when using a new notation like [!tagged-call_user_func ..].
That said it doesn't really make sense to collect a list of objects, extract them to be function arguments just to let PHP put them back into a list again. I get your idea behind it in terms of code cleanliness though.
Another limitation is the fact that you can't pass multiple variadic arguments to a function. So ...
public function __construct(Alpha ...$alphas, Beta ...$betas)
... is not possible.
A possible solution/workaround allowing you to keep the typehinting for the collection would be the following:
final class SynchronousMessageDispatcher implements MessageDispatcher
{
/**
* #var Consumer[]
*/
private $consumers;
public function __construct(iterable $consumers)
{
foreach($consumers as $consumer) {
assert($consumer instanceof Consumer, \InvalidArgumentException('..'));
}
$this->consumers = $consumers;
}
}