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> Symfony 7 > Dependency Injection #[Attributes]
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05.

Container and Iterator with ServiceCollectionInterface

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In the last chapter, we made these buttons listed programmatically. But when we did that, we broke the actual button-press functionality! Whoops! The kids are getting restless: we need to fix this.

Over in ButtonRemote, there are a couple of ways to solve this. The first approach, which is probably the easiest, is to inject two arguments: one that's an iterator of the button services and one that's a locator, meaning a mini-container with a get() method for fetching each service. That would work and it's perfectly valid. But we can do better!

ServiceCollectionInterface

We can inject an object that's both an iterator and a locator: ServiceCollectionInterface. Let's take a look at that. This a ServiceProviderInterface (that's the locator) and an IteratorAggregate (that's the iterator). For good measure, it's also Countable.

Back in ButtonRemote, we need to switch AutowireIterator back to AutowireLocator for Symfony to inject the ServiceCollectionInterface:

32 lines | src/Remote/ButtonRemote.php
// ... lines 1 - 8
final class ButtonRemote
{
public function __construct(
#[AutowireLocator(ButtonInterface::class, indexAttribute: 'key')]
private ServiceCollectionInterface $buttons,
) {
}
// ... lines 16 - 30
}

I'll clean up some unused imports here, and... nice.

Back in our app, refresh and... Okay, we're still listing the buttons, so that's a good sign. Now, if we click a button... it looks like this is working again! Pop into the profiler to check the POST request to see that the proper button logic is still being called. Sweet!

Laziness

One of the great things about a service locator is that it's lazy. Services aren't instantiated until and unless we call get() to fetch them. And even then, only a single service is created, even if we go nuts and call get() for the same service a bunch of times.

I love being lazy but we have a problem. Down here, in buttons(), we're iterating over all the buttons. This is forcing the instantiation of all the button services just to get their $name's. Since we just care about the names, this is a waste!

ServiceCollectionInterface::getProvidedServices()

ServiceCollectionInterface to the rescue! Symfony service locators have a special method called getProvidedServices(). Remove all this code and dd($this->buttons->getProvidedServices()) to see what it returns:

34 lines | src/Remote/ButtonRemote.php
// ... lines 1 - 8
final class ButtonRemote
{
// ... lines 11 - 24
public function buttons(): iterable
{
dd($this->buttons->getProvidedServices());
// ... lines 28 - 31
}
}

Jump back to our app and refresh. This looks almost identical to the manual mapping we previously used with #[AutowireLocator].

We want the keys of this array. Back here, return array_keys() of $this->buttons->getProvidedServices():

30 lines | src/Remote/ButtonRemote.php
// ... lines 1 - 8
final class ButtonRemote
{
// ... lines 11 - 24
public function buttons(): iterable
{
return array_keys($this->buttons->getProvidedServices());
}
}

Go back to the app and... refresh. Everything is still working and behind the scenes, we're no longer instantiating all the button services.

Performance win!

To celebrate, let's add a new button to our remote!

Adding a Mute Button

Create a new PHP class called MuteButton and have it implement ButtonInterface. Press Ctrl+Enter to generate the press() method. Inside, write dump('Pressed mute button'). Now, add #[AsTaggedItem] with an $index of mute. Leave the priority as the default, 0. This will slot this button below the others:

15 lines | src/Remote/Button/MuteButton.php
// ... lines 1 - 6
#[AsTaggedItem('mute')]
final class MuteButton implements ButtonInterface
{
public function press(): void
{
dump('Mute button pressed');
}
}

There's just one other thing we need to do. Each button has an SVG icon in assets/icons with the same name as the button. Copy the mute.svg file from tutorial/ and paste it here.

Moment of truth! Go back to our app, refresh, and... there it is! Click it and check the profiler. It's working! Now we can mute the TV when the kids are watching Barney. Perfect!

That's it for this refactor! Adding buttons is simple and performant.

Next, let's add logging to our remote and learn about our next attribute: #[AsAlias].