How to Write a custom Twig Extension

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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 article 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:

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

use Twig\Extension\AbstractExtension;
use Twig\TwigFilter;

class AppExtension extends AbstractExtension
{
    public function getFilters()
    {
        return array(
            new TwigFilter('price', array($this, 'formatPrice')),
        );
    }

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

        return $price;
    }
}

Note

Prior to Twig 1.26, your extension had to define an additional getName() method that returned a string with the extension's internal name (e.g. app.my_extension). When your extension needs to be compatible with Twig versions before 1.26, include this method which is omitted in the example above.

Here's how to create a custom function:

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

use Twig\Extension\AbstractExtension;
use Twig\TwigFunction;

class AppExtension extends AbstractExtension
{
    public function getFunctions()
    {
        return array(
            new TwigFunction('area', array($this, 'calculateArea')),
        );
    }

    public function calculateArea(int $width, int $length)
    {
        return $width * $length;
    }
}

Tip

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

Register an Extension as a Service

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

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# app/config/services.yml
services:
    app.twig_extension:
        class: AppBundle\Twig\AppExtension
        public: false
        tags:
            - { name: twig.extension }

Using the custom Extension

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

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{# Using the filter without arguments. Outputs $5,500.00 #}
{{ '5500'|price }}

{# Passing arguments to the filter. Outputs $5500,2516 #}
{{ '5500.25155'|price(4, ',', '') }}

{# Passing arguments to the function. Outputs 140 #}
Total area: {{ area(20, 7) }}

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.
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