Service Method Calls and Setter Injection

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Tip

If you're using autowiring, you can use #[Required] to automatically configure method calls.

Usually, you'll want to inject your dependencies via the constructor. But sometimes, especially if a dependency is optional, you may want to use "setter injection". For example:

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// src/Service/MessageGenerator.php
namespace App\Service;

use Psr\Log\LoggerInterface;

class MessageGenerator
{
    private LoggerInterface $logger;

    public function setLogger(LoggerInterface $logger): void
    {
        $this->logger = $logger;
    }

    // ...
}

To configure the container to call the setLogger method, use the calls key:

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# config/services.yaml
services:
    App\Service\MessageGenerator:
        # ...
        calls:
            - setLogger: ['@logger']

To provide immutable services, some classes implement immutable setters. Such setters return a new instance of the configured class instead of mutating the object they were called on:

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// src/Service/MessageGenerator.php
namespace App\Service;

use Psr\Log\LoggerInterface;

class MessageGenerator
{
    private LoggerInterface $logger;

    public function withLogger(LoggerInterface $logger): self
    {
        $new = clone $this;
        $new->logger = $logger;

        return $new;
    }

    // ...
}

Because the method returns a separate cloned instance, configuring such a service means using the return value of the wither method ($service = $service->withLogger($logger);). The configuration to tell the container it should do so would be like:

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# config/services.yaml
services:
    App\Service\MessageGenerator:
        # ...
        calls:
            - withLogger: !returns_clone ['@logger']

Tip

If autowire is enabled, you can also use attributes; with the previous example it would be:

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#[Required]
public function withLogger(LoggerInterface $logger): static
{
    $new = clone $this;
    $new->logger = $logger;

    return $new;
}

If you don't want a method with a static return type and a #[Required] attribute to behave as a wither, you can add a @return $this annotation to disable the returns clone feature.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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