Symfony\Bundle\TwigBundle\Extension\ContainerExtension example

ContainerExtension.php

<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Bundle\TwigBundle\Extension;

use Symfony\Bundle\TwigBundle\TokenParser\RenderTokenParser;
use Symfony\Component\DependencyInjection\ContainerInterface;

class ContainerExtension extends \Twig_Extension
{
    private $container;

    public function __construct(ContainerInterface $container)
    {
        $this->container = $container;
    }

    public function getFunctions()
    {
        return array(
            'container_param' => new \Twig_Function_Method($this, 'getParameter'),
        );
    }

    public function getParameter($key)
    {
        return $this->container->getParameter($key);
    }

    public function getName()
    {
        return 'container';
    }
}

index.html.twig

{{ container_param('kernel.root_dir') }}

twig.xml

<?xml version="1.0" ?>

<container xmlns="http://symfony.com/schema/dic/services"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">

    <parameters>
           :
        <parameter key="twig.extension.container.class">Symfony\Bundle\TwigBundle\Extension\ContainerExtension</parameter>
           : 
   </parameters>

    <services>
           :
        <service id="twig.extension.container" class="%twig.extension.container.class%" public="false">
            <tag name="twig.extension" />
            <argument type="service" id="service_container" />
        </service>
           :
    </services>
</container>