added documentation on how to extend bundle services

Author: Bart van den Burg

cookbook/bundles/override.rst

@@ -7,6 +7,13 @@ How to Override any Part of a Bundle
 This document is a quick reference for how to override different parts of
 third-party bundles.
 
+.. note::
+
+    Whenever you are extending a (part of a) bundle, make sure that your bundle
+    is registered in the kernel **after** the bundle you're trying to override
+    parts of. Otherwise, your config that is supposed to override bundle 
+    configuration, is instead overridden by it!
+
 Templates
 ---------
 
@@ -35,7 +42,40 @@ inheritance. For more information, see :doc:`/cookbook/bundles/inheritance`.
 Services & Configuration
 ------------------------
 
-In progress...
+In order to completely override a service, just define the service as you would
+usual, but making sure the id of the service is identical to the one you are
+overriding.
+
+In order to extend a service (e.g. just add a method, but leaving the
+dependencies or tags intact), make sure the class name is defined as a parameter
+in the service config of the bundle containing the service. Then, in your bundle
+you can override the class name by setting the parameter directly in the
+container in the Extension class of your bundle:
+
+.. code-block:: html+php
+    <?php
+
+    namespace Foo\BarBundle\DependencyInjection;
+
+    use Symfony\Component\DependencyInjection\ContainerBuilder;
+    use Symfony\Component\Config\FileLocator;
+    use Symfony\Component\HttpKernel\DependencyInjection\Extension;
+    use Symfony\Component\DependencyInjection\Loader;
+
+    class FooBarExtension extends Extension
+    {
+
+        public function load(array $configs, ContainerBuilder $container)
+        {
+            $configuration = new Configuration();
+            $config = $this->processConfiguration($configuration, $configs);
+
+            $container->setParameter('parameter_name.containing.service_class', 'Foo\BarBundle\Service\Service');
+
+            $loader = new Loader\XmlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
+            $loader->load('services.xml');
+        }
+    }
 
 Entities & Entity mapping
 -------------------------