> Symfony 7 > Dependency Injection #[Attributes]
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09.

Enable Services in Specific Environments with When

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Wouldn't it be cool if we had a special secret button on our remote we could use to make sure it's working correctly? Of course it would! Let's add a sneaky new "Diagnostics" button that will only be available in the dev environment.

Adding a Diagnostics Button

In App\Remote\Button, create a new class: DiagnosticsButton. Make it implement ButtonInterface... and hold "control" + "enter" to add the press() method. Inside, we'll dump('Pressed diagnostics button.')... and, just like before, add #[AsTaggedItem] with diagnostics as the index:

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

Finally, copy the diagnostics.svg file from the tutorial/ directory into assets/icons/.

Spin over to our app and refresh... new button! And if we press it... it even looks like it's working! We're pretty impressive remote control developers!

#[When]

Our new button is automatically registered with the service container, but we want it only in the dev environment. The #[When] attribute is perfect for this. Back in DiagnosticsButton, add #[When] with dev as the argument:

17 lines | src/Remote/Button/DiagnosticsButton.php
// ... lines 1 - 8
#[When('dev')]
final class DiagnosticsButton implements ButtonInterface
// ... lines 11 - 17

Thanks to this, the class will be completely ignored by the service container unless we're in the dev environment. Head over and refresh. It's still there. That makes sense: we are in the dev environment. So let's fudge this a bit. Change the #[When] argument from dev to prod - so we can see it working:

17 lines | src/Remote/Button/DiagnosticsButton.php
// ... lines 1 - 8
#[When('prod')]
final class DiagnosticsButton implements ButtonInterface
// ... lines 11 - 17

Refresh again and... boom! The button is gone! Awesome!

#[Exclude]

Now that this is working, let's talk about the cousin of #[When]: #[Exclude]. This is like a big warning sign that tells Symfony to never, ever register a specific class as a service in the service container. Right now, in config/services.yaml, this App/: section tells Symfony to autowire every class in the src/ directory. Inside App/:, we have this exclude key. That contains a list of paths Symfony should ignore and is the traditional way to exclude classes from being registered as services. It's fine, but I find it a bit clunky. This is where #[Exclude] comes in.

In MuteButton, up here, add #[Exclude]...

17 lines | src/Remote/Button/MuteButton.php
// ... lines 1 - 8
#[Exclude]
final class MuteButton implements ButtonInterface
// ... lines 11 - 17

then head back to our app and refresh. The "Mute" button is gone! It worked.

This won't be a super common attribute in your app, but hey! This is the DI attribute tutorial! So you get to see all the neat stuff!

Next: Let's talk about lazy services.