How to Inject Values Based on Complex Expressions

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How to Inject Values Based on Complex Expressions

The service container also supports an "expression" that allows you to inject very specific values into a service.

For example, suppose you have a service (not shown here), called App\Mail\MailerConfiguration, which has a getMailerMethod() method on it. This returns a string - like sendmail based on some configuration.

Suppose that you want to pass the result of this method as a constructor argument to another service: App\Mailer. One way to do this is with an expression:

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# config/services.yaml
services:
    # ...

    App\Mail\MailerConfiguration: ~

    App\Mailer:
        # the '@=' prefix is required when using expressions for arguments in YAML files
        arguments: ['@=service("App\\Mail\\MailerConfiguration").getMailerMethod()']
        # when using double-quoted strings, the backslash needs to be escaped twice (see https://yaml.org/spec/1.2/spec.html#id2787109)
        # arguments: ["@=service('App\\\\Mail\\\\MailerConfiguration').getMailerMethod()"]

To learn more about the expression language syntax, see The Expression Syntax.

In this context, you have access to 2 functions:

service
Returns a given service (see the example above).
parameter
Returns a specific parameter value (syntax is like service).

You also have access to the Container via a container variable. Here's another example:

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# config/services.yaml
services:
    App\Mailer:
        # the '@=' prefix is required when using expressions for arguments in YAML files
        arguments: ["@=container.hasParameter('some_param') ? parameter('some_param') : 'default_value'"]

Expressions can be used in arguments, properties, as arguments with configurator and as arguments to calls (method calls).

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