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How to Write a custom Twig Extension

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How to Write a custom Twig Extension

The main motivation for writing an extension is to move often used code into a reusable class like adding support for internationalization. An extension can define tags, filters, tests, operators, global variables, functions, and node visitors.

Creating an extension also makes for a better separation of code that is executed at compilation time and code needed at runtime. As such, it makes your code faster.

Tip

Before writing your own extensions, have a look at the Twig official extension repository.

Create the Extension Class

Note

This cookbook describes how to write a custom Twig extension as of Twig 1.12. If you are using an older version, please read Twig extensions documentation legacy.

To get your custom functionality you must first create a Twig Extension class. As an example you’ll create a price filter to format a given number into price:

// src/AppBundle/Twig/AppExtension.php
namespace AppBundle\Twig;

class AppExtension extends \Twig_Extension
{
    public function getFilters()
    {
        return array(
            new \Twig_SimpleFilter('price', array($this, 'priceFilter')),
        );
    }

    public function priceFilter($number, $decimals = 0, $decPoint = '.', $thousandsSep = ',')
    {
        $price = number_format($number, $decimals, $decPoint, $thousandsSep);
        $price = '$'.$price;

        return $price;
    }

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

Tip

Along with custom filters, you can also add custom functions and register global variables.

Register an Extension as a Service

Now you must let the Service Container know about your newly created Twig Extension:

  • YAML
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    # app/config/services.yml
services:
    app.twig_extension:
        class: AppBundle\Twig\AppExtension
        public: false
        tags:
            - { name: twig.extension }
  • XML
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    <!-- app/config/services.xml -->
<services>
    <service id="app.twig_extension"
        class="AppBundle\Twig\AppExtension"
        public="false">
        <tag name="twig.extension" />
    </service>
</services>
  • PHP
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    // app/config/services.php
use Symfony\Component\DependencyInjection\Definition;

$container
    ->register('app.twig_extension', '\AppBundle\Twig\AppExtension')
    ->setPublic(false)
    ->addTag('twig.extension');

Note

Keep in mind that Twig Extensions are not lazily loaded. This means that there’s a higher chance that you’ll get a Symfony\Component\DependencyInjection\Exception\ServiceCircularReferenceException or a Symfony\Component\DependencyInjection\Exception\ScopeWideningInjectionException if any services (or your Twig Extension in this case) are dependent on the request service. For more information take a look at How to Work with Scopes.

Using the custom Extension

Using your newly created Twig Extension is no different than any other:

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{# outputs $5,500.00 #}
{{ '5500'|price }}

Passing other arguments to your filter:

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{# outputs $5500,2516 #}
{{ '5500.25155'|price(4, ',', '') }}

Learning further

For a more in-depth look into Twig Extensions, please take a look at the Twig extensions documentation.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.