fix(code): fix on both code & service conf

Small fix on code and service configuration.

Author: Guikingone

service_container/injection_types.rst

@@ -266,9 +266,19 @@ this approach allow you to make a service immutable::
             $this->mailer = $mailer;
         }
         
+        /**
+         *
+         * The @return is required.
+         *
+         * @return static
+         *
+         */
         public function withMailer(MailerInterface $mailer)
         {
-            return new static($mailer);
+            $new = clone $this;
+            $new->mailer = $mailer;
+            
+            return $new
         }
 
         // ...
@@ -303,9 +313,8 @@ which allow the container to return the newly created service:
                 <!-- ... -->
 
                 <service id="app.newsletter_manager" class="App\Mail\NewsletterManager">
-                    <call method="withMailer">
+                    <call method="withMailer" use-result=true>
                         <argument type="service" id="mailer" />
-                        <use-result />
                     </call>
                 </service>
             </services>
@@ -319,7 +328,7 @@ which allow the container to return the newly created service:
 
         // ...
         $container->register('app.newsletter_manager', NewsletterManager::class)
-            ->addMethodCall('withMailer', [new Reference('mailer')], 'use_result' => true);
+            ->addMethodCall('withMailer', [new Reference('mailer')], true);
 
 This approach is useful if you need to configure your service according to your needs, 
 so, what are the advantages?
@@ -329,3 +338,9 @@ so, what are the advantages?
 
 * You can easily change the injected service as long as it respect the interface 
   asked by the initial service.
+
+* It allow you to get rid of factory usages which can lead a more complex code
+
+The disadvantages of this approach are:
+
+*