In my Silex project I’m currently using the Twig template engine. It’s a truly great template compiler. But it’s so much more than that. Just a copy paste from the Twig website:

• Fast: Twig compiles templates down to plain optimized PHP code. The overhead compared to regular PHP code was reduced to the very minimum.
• Secure: Twig has a sandbox mode to evaluate untrusted template code. This allows Twig to be used as a template language for applications where users may modify the template design.
• Flexible: Twig is powered by a flexible lexer and parser. This allows the developer to define its own custom tags and filters, and create its own DSL.

For me, it took me some time to get used to this way of using PHP and templates, but the Twig project is greatly documented. Guaranteed solutions can be found on their documentation pages.

I wanted to extend Twig to use my custom classes and methods. I have a web application with registered users who have an email address. I want to show their gravatar as distinct users in my layout.
I don’t want to create HTML code from within my controllers, but I want something like this:

   <div class="users">
      {% for user in users %}
         <img title="{{ user.name }}" alt="{{ user.name }}" src="{{ user.email|gravatar }}" />
      {% endfor %}
   </div>

First of, we need to create a class where we will put our filters which extends \Twig_Extension. This class can be stored anywhere, just make sure your namespace can be used in your bootstrap file. This could look something like this:

We need to overwrite the abstract methods getFilters which will need to return all your filters you want to use. (As stated in the abstract class \Twig_Extension: Returns a list of filters to add to the existing list.). The getName() method must return an unique identifier for your extension.

Next we need to tell Twig that we have custom filters we want to use (after registering).

use Silex\Provider\TwigServiceProvider;

$app->register(new TwigServiceProvider(), array(
    'twig.path' => __DIR__ . '/../web/public/views'
));

$app['twig'] = $app->extend("twig", function (\Twig_Environment $twig, Silex\Application $app) {
    $twig->addExtension(new Classes\Utils\Filters($app));

    return $twig;
});