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'