minor #9990 Tell about ServiceLocatorTagPass::register() (nicolas-grekas, javiereguiluz)

This PR was merged into the 3.4 branch.

Discussion
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Tell about ServiceLocatorTagPass::register()

Fixes #7784

Commits
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b3a3905 Minor reword
7f1c584 Tell about ServiceLocatorTagPass::register()

Author: javiereguiluz

service_container/service_subscribers_locators.rst

@@ -349,9 +349,24 @@ Now you can use the service locator by injecting it in any other service:
             ->setArguments(array(new Reference('app.command_handler_locator')))
         ;
 
-.. tip::
+In :doc:`compiler passes </service_container/compiler_passes>` it's recommended
+to use the :method:`Symfony\\Component\\DependencyInjection\\Compiler\\ServiceLocatorTagPass::register`
+method to create the service locators. This will save you some boilerplate and
+will share identical locators amongst all the services referencing them::
+
+    use Symfony\Component\DependencyInjection\Compiler\ServiceLocatorTagPass;
+    use Symfony\Component\DependencyInjection\ContainerBuilder;
+
+    public function process(ContainerBuilder $container)
+    {
+        //...
+
+        $locateableServices = array(
+            //...
+            'logger' => new Reference('logger'),
+        );
 
-    If the service locator is not intended to be used by multiple services, it's
-    better to create and inject it as an anonymous service.
+        $myService->addArgument(ServiceLocatorTagPass::register($locateableServices));
+    }
 
 .. _`Command pattern`: https://en.wikipedia.org/wiki/Command_pattern