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+Create your own framework... on top of the Symfony2 Components (part 5)
+=======================================================================
+
+The astute reader has noticed that our framework hardcodes the way specific
+"code" (the templates) is run. For simple pages like the ones we have created
+so far, that's not a problem, but if you want to add more logic, you would be
+forced to put the logic into the template itself, which is probably not a good
+idea, especially if you still have the separation of concerns principle in
+mind.
+
+Let's separate the template code from the logic by adding a new layer: the
+controller: *The controller mission is to generate a Response based on the
+information conveyed by the client Request.*
+
+Change the template rendering part of the framework to read as follows::
+
+    <?php
+
+    // example.com/web/front.php
+
+    // ...
+
+    try {
+        $request->attributes->add($matcher->match($request->getPathInfo()));
+        $response = call_user_func('render_template', $request);
+    } catch (Routing\Exception\ResourceNotFoundException $e) {
+        $response = new Response('Not Found', 404);
+    } catch (Exception $e) {
+        $response = new Response('An error occurred', 500);
+    }
+
+As the rendering is now done by an external function (``render_template()``
+here), we need to pass to it the attributes extracted from the URL. We could
+have passed them as an additional argument to ``render_template()``, but
+instead, let's use another feature of the ``Request`` class called
+*attributes*: Request attributes lets you attach additional information about
+the Request that is not directly related to the HTTP Request data.
+
+You can now create the ``render_template()`` function, a generic controller
+that renders a template when there is no specific logic. To keep the same
+template as before, request attributes are extracted before the template is
+rendered::
+
+    function render_template($request)
+    {
+        extract($request->attributes->all(), EXTR_SKIP);
+        ob_start();
+        include sprintf(__DIR__.'/../src/pages/%s.php', $_route);
+
+        return new Response(ob_get_clean());
+    }
+
+As ``render_template`` is used as an argument to the PHP ``call_user_func()``
+function, we can replace it with any valid PHP `callbacks`_. This allows us to
+use a function, an anonymous function, or a method of a class as a
+controller... your choice.
+
+As a convention, for each route, the associated controller is configured via
+the ``_controller`` route attribute::
+
+    $routes->add('hello', new Routing\Route('/hello/{name}', array(
+        'name' => 'World',
+        '_controller' => 'render_template',
+    )));
+
+    try {
+        $request->attributes->add($matcher->match($request->getPathInfo()));
+        $response = call_user_func($request->attributes->get('_controller'), $request);
+    } catch (Routing\Exception\ResourceNotFoundException $e) {
+        $response = new Response('Not Found', 404);
+    } catch (Exception $e) {
+        $response = new Response('An error occurred', 500);
+    }
+
+A route can now be associated with any controller and of course, within a
+controller, you can still use the ``render_template()`` to render a template::
+
+    $routes->add('hello', new Routing\Route('/hello/{name}', array(
+        'name' => 'World',
+        '_controller' => function ($request) {
+            return render_template($request);
+        }
+    )));
+
+This is rather flexible as you can change the Response object afterwards and
+you can even pass additional arguments to the template::
+
+    $routes->add('hello', new Routing\Route('/hello/{name}', array(
+        'name' => 'World',
+        '_controller' => function ($request) {
+            // $foo will be available in the template
+            $request->attributes->set('foo', 'bar');
+
+            $response = render_template($request);
+
+            // change some header
+            $response->headers->set('Content-Type', 'text/plain');
+
+            return $response;
+        }
+    )));
+
+Here is the updated and improved version of our framework::
+
+    <?php
+
+    // example.com/web/front.php
+
+    require_once __DIR__.'/../vendor/.composer/autoload.php';
+
+    use Symfony\Component\HttpFoundation\Request;
+    use Symfony\Component\HttpFoundation\Response;
+    use Symfony\Component\Routing;
+
+    function render_template($request)
+    {
+        extract($request->attributes->all(), EXTR_SKIP);
+        ob_start();
+        include sprintf(__DIR__.'/../src/pages/%s.php', $_route);
+
+        return new Response(ob_get_clean());
+    }
+
+    $request = Request::createFromGlobals();
+    $routes = include __DIR__.'/../src/app.php';
+
+    $context = new Routing\RequestContext();
+    $context->fromRequest($request);
+    $matcher = new Routing\Matcher\UrlMatcher($routes, $context);
+
+    try {
+        $request->attributes->add($matcher->match($request->getPathInfo()));
+        $response = call_user_func($request->attributes->get('_controller'), $request);
+    } catch (Routing\Exception\ResourceNotFoundException $e) {
+        $response = new Response('Not Found', 404);
+    } catch (Exception $e) {
+        $response = new Response('An error occurred', 500);
+    }
+
+    $response->send();
+
+To celebrate the birth of our new framework, let's create a brand new
+application that needs some simple logic. Our application has one page that
+says whether a given year is a leap year or not. When calling
+``/is_leap_year``, you get the answer for the current year, but the you can
+also specify a year like in ``/is_leap_year/2009``. Being generic, the
+framework does not need to be modified in any way, just create a new
+``app.php`` file::
+
+    <?php
+
+    // example.com/src/app.php
+
+    use Symfony\Component\Routing;
+    use Symfony\Component\HttpFoundation\Response;
+
+    function is_leap_year($year = null) {
+        if (null === $year) {
+            $year = date('Y');
+        }
+
+        return 0 == $year % 400 || (0 == $year % 4 && 0 != $year % 100);
+    }
+
+    $routes = new Routing\RouteCollection();
+    $routes->add('leap_year', new Routing\Route('/is_leap_year/{year}', array(
+        'year' => null,
+        '_controller' => function ($request) {
+            if (is_leap_year($request->attributes->get('year'))) {
+                return new Response('Yep, this is a leap year!');
+            }
+
+            return new Response('Nope, this is not a leap year.');
+        }
+    )));
+
+    return $routes;
+
+The ``is_leap_year()`` function returns ``true`` when the given year is a leap
+year, ``false`` otherwise. If the year is null, the current year is tested.
+The controller is simple: it gets the year from the request attributes, pass
+it to the `is_leap_year()`` function, and according to the return value it
+creates a new Response object.
+
+As always, you can decide to stop here and use the framework as is; it's
+probably all you need to create simple websites like those fancy one-page
+`websites`_ and hopefully a few others.
+
+.. _`callbacks`: http://php.net/callback#language.types.callback
+.. _`websites`:  http://kottke.org/08/02/single-serving-sites