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()"]Learn more about the expression language syntax.
In this context, you have access to 3 functions:
service- Returns a given service (see the example above).
parameter- Returns a specific parameter value (syntax is like
service). env- Returns the value of an env variable.
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, as arguments to calls (method calls) and in factories (service factories).