Why Lazy Services?

In some cases, you may want to inject a service that is a bit heavy to instantiate, but is not always used inside your object. For example, imagine you have a NewsletterManager and you inject a mailer service into it. Only a few methods on your NewsletterManager actually use the mailer, but even when you don't need it, a mailer service is always instantiated in order to construct your NewsletterManager.

Configuring lazy services is one answer to this. With a lazy service, a "proxy" of the mailer service is actually injected. It looks and acts just like the mailer, except that the mailer isn't actually instantiated until you interact with the proxy in some way.

Installation

In order to use the lazy service instantiation, you will first need to install the ProxyManager bridge:

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$ composer require symfony/proxy-manager-bridge:~2.3

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$ composer require ocramius/proxy-manager:~1.0

Configuration

You can mark the service as lazy by manipulating its definition:

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services:
   foo:
     class: Acme\Foo
     lazy: true

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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="Acme\Foo" lazy="true" />
    </services>
</container>

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use Symfony\Component\DependencyInjection\Definition;

$definition = new Definition('Acme\Foo');
$definition->setLazy(true);
$container->setDefinition('foo', $definition);

You can then require the service from the container:

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$service = $container->get('foo');

At this point the retrieved $service should be a virtual proxy with the same signature of the class representing the service. You can also inject the service just like normal into other services. The object that's actually injected will be the proxy.

To check if your proxy works you can simply check the interface of the received object.

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var_dump(class_implements($service));

If the class implements the ProxyManager\Proxy\LazyLoadingInterface your lazy loaded services are working.

The proxy gets initialized and the actual service is instantiated as soon as you interact in any way with this object.

Additional Resources

You can read more about how proxies are instantiated, generated and initialized in the documentation of ProxyManager.