How to Create Service Aliases and Mark Services as Private

Marking Services as Public / Private

When defining services, you'll usually want to be able to access these definitions within your application code. These services are called public. For example, the doctrine service is a public service. This means that you can fetch it from the container using the get() method:

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$doctrine = $container->get('doctrine');

In some cases, a service only exists to be injected into another service and is not intended to be fetched directly from the container as shown above.

In these cases, to get a minor performance boost, you can set the service to be not public (i.e. private):

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services:
    foo:
        class: Example\Foo
        public: false

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<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="foo" class="Example\Foo" public="false" />
    </services>
</container>

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use Example\Foo;

$container->register('foo', Foo::class)
    ->setPublic(false);

What makes private services special is that, if they are only injected once, they are converted from services to inlined instantiations (e.g. new PrivateThing()). This increases the container's performance.

Now that the service is private, you must not fetch the service directly from the container:

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$container->get('foo');

Simply said: A service can be marked as private if you do not want to access it directly from your code.

However, if a service has been marked as private, you can still alias it (see below) to access this service (via the alias).

Aliasing

You may sometimes want to use shortcuts to access some services. You can do so by aliasing them and, furthermore, you can even alias non-public services.

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services:
    app.phpmailer:
        class: AppBundle\Mail\PhpMailer

    app.mailer:
        alias: app.phpmailer

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<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="app.phpmailer" class="AppBundle\Mail\PhpMailer" />

        <service id="app.mailer" alias="app.phpmailer" />
    </services>
</container>

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use AppBundle\Mail\PhpMailer;

$container->register('app.phpmailer', PhpMailer::class);

$container->setAlias('app.mailer', 'app.phpmailer');

This means that when using the container directly, you can access the app.phpmailer service by asking for the app.mailer service like this:

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$container->get('app.mailer'); // Would return a PhpMailer instance

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services:
    # ...
    app.mailer: '@app.phpmailer'

Anonymous Services

In some cases, you may want to prevent a service being used as a dependency of other services. This can be achieved by creating an anonymous service. These services are like regular services but they don't define an ID and they are created where they are used.

The following example shows how to inject an anonymous service into another service:

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<!-- app/config/services.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services
        http://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="foo" class="AppBundle\Foo">
            <argument type="service">
                <service class="AppBundle\AnonymousBar" />
            </argument>
        </service>
    </services>
</container>

Deprecating Services

Once you have decided to deprecate the use of a service (because it is outdated or you decided not to maintain it anymore), you can deprecate its definition:

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acme.my_service:
    class: ...
    deprecated: The "%service_id%" service is deprecated since 2.8 and will be removed in 3.0.

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<?xml version="1.0" encoding="UTF-8" ?>
<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-Instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

    <services>
        <service id="acme.my_service" class="...">
            <deprecated>The "%service_id%" service is deprecated since 2.8 and will be removed in 3.0.</deprecated>
        </service>
    </services>
</container>

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$container
    ->register('acme.my_service', '...')
    ->setDeprecated(
        true,
        'The "%service_id%" service is deprecated since 2.8 and will be removed in 3.0.'
    )
;

Now, every time this service is used, a deprecation warning is triggered, advising you to stop or to change your uses of that service.

The message is actually a message template, which replaces occurrences of the %service_id% placeholder by the service's id. You must have at least one occurrence of the %service_id% placeholder in your template.

For service decorators (see above), if the definition does not modify the deprecated status, it will inherit the status from the definition that is decorated.