As of 2014 things have changed improved a lot in the Symfony / Silex world, compared to 2011, when i first blogged about twig extensions in Silex.
Things got more easy, yay!
As Composer appeared, installation and autoloading is a breeze nowadays.
I presume here, that you have installed your Silex project via composer.
If so, you can install the twig extensions like this:
Just go to your project folder and run:
composer require twig/extensions:~1.0
and your done with installation and autoloading.
Now to integration and service registration, this also got more easy.
Place this after you have registered the twig service:
$app['twig'] = $app->share($app->extend('twig', function($twig, $app) { $twig->addExtension(new Twig_Extensions_Extension_Text($app)); return $twig; }));
Thats it, now you can use the text filters in your twig templates:
{{ post.content|truncate(200)|raw }}
Easy…