[DI] Add section about Service Closures

HypeMC · HypeMC · commit 722e76eba180 · 2022-10-01T16:19:21.000+02:00
diff --git a/service_container/lazy_services.rst b/service_container/lazy_services.rst
@@ -6,7 +6,8 @@ Lazy Services
 
 .. seealso::
 
-    Another way to inject services lazily is via a :doc:`service subscriber </service_container/service_subscribers_locators>`.
+    Other ways to inject services lazily is via a :doc:`service closure </service_container/service_closures>` or
+    :doc:`service subscriber </service_container/service_subscribers_locators>`.
 
 Why Lazy Services?
 ------------------
diff --git a/service_container/service_closures.rst b/service_container/service_closures.rst
@@ -0,0 +1,92 @@
+.. index::
+    single: DependencyInjection; Service Closures
+
+Service Closures
+================
+
+This feature wraps the injected service into a closure allowing it to be
+lazily loaded when and if needed.
+This is useful if the service being injected is a bit heavy to instantiate
+or is used only in certain cases.
+The service is instantiated the first time the closure is called, while
+all subsequent calls return the same instance, unless the service is
+:doc:`not shared </service_container/shared>`::
+
+    // src/Service/MyService.php
+    namespace App\Service;
+
+    use Symfony\Component\Mailer\MailerInterface;
+
+    class MyService
+    {
+        /**
+         * @var callable(): MailerInterface
+         */
+        private \Closure $mailer;
+
+        public function __construct(\Closure $mailer)
+        {
+            $this->mailer = $mailer;
+        }
+
+        public function doSomething(): void
+        {
+            // ...
+
+            $this->getMailer()->send($email);
+        }
+
+        private function getMailer(): MailerInterface
+        {
+            return ($this->mailer)();
+        }
+    }
+
+To define a service closure and inject it to another service, create an
+argument of type ``service_closure``:
+
+.. configuration-block::
+
+    .. code-block:: yaml
+
+        # config/services.yaml
+        services:
+            App\Service\MyService:
+                arguments: [!service_closure '@mailer']
+
+    .. code-block:: xml
+
+        <!-- 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 https://symfony.com/schema/dic/services/services-1.0.xsd">
+
+            <services>
+
+                <service id="App\Service\MyService">
+                    <argument type="service_closure" id="mailer"/>
+                </service>
+
+            </services>
+        </container>
+
+    .. code-block:: php
+
+        // config/services.php
+        namespace Symfony\Component\DependencyInjection\Loader\Configurator;
+
+        use App\Service\MyService;
+        use Symfony\Component\DependencyInjection\Argument\ServiceClosureArgument;
+        use Symfony\Component\DependencyInjection\Reference;
+
+        return function (ContainerConfigurator $configurator) {
+            $services = $configurator->services();
+
+            $services->set(MyService::class)
+                ->args([new ServiceClosureArgument(new Reference('mailer'))]);
+        };
+
+.. seealso::
+
+    Another way to inject services lazily is via a :doc:`service locators </service_container/service_subscribers_locators>`.
diff --git a/service_container/service_subscribers_locators.rst b/service_container/service_subscribers_locators.rst
@@ -12,6 +12,10 @@ instantiation of the services to be lazy. However, that's not possible using
 the explicit dependency injection since services are not all meant to
 be ``lazy`` (see :doc:`/service_container/lazy_services`).
 
+.. seealso::
+
+    Another way to inject services lazily is via a :doc:`service closure </service_container/service_closures>`.
+
 This can typically be the case in your controllers, where you may inject several
 services in the constructor, but the action called only uses some of them.
 Another example are applications that implement the `Command pattern`_
