How can I create a symfony twig filter?

For instance my bundle namespace is Facebook\Bundle\FacebookBundle\Extension.

Using this how can I create a twig extension ?

You can also create twig functions by using the getFunctions()

class FacebookExtension extends Twig_Extension
{
    public function getFunctions()
    {
        return array(
            'myFunction' => new Twig_Filter_Method($this, 'myFunction'),
        );
    }

    public function myFunction($arg1)
    {
        return $arg1;
    }

Use your function like this:

{{ myFunction('my_param') }}