Decoding JSON in Twig

Is is possible to decode JSON in twig? Googling doesn't seem to yield anything about this. Does decoding JSON in Twig not make sense?

---

I'm trying to access 2 entity properties on an Symfony2's entity field type (Entity Field Type).

After coming across 2 previous SO questions ( Symfony2 entity field type alternatives to "property" or "__toString()"? and Symfony 2 Create a entity form field with 2 properties ) which suggested adding an extra method to an entity to retrieve a customized string rather than an entity attribute, I thought of (and did) returning a JSON string representing an object instance.

Somewhere in the entity class:

/**
 * Return a JSON string representing this class.
 */
public function getJson()
{
   return json_encode(get_object_vars($this));
}

And in the form (something like):

$builder->add('categories', 'entity', array (
...
'property' => 'json',
...
));

Afterwards, I was hoping to json_decode it in Twig...

{% for category in form.categories %}
    {# json_decode() part is imaginary #}
    {% set obj = category.vars.label|json_decode() %}
{% endfor %}

That's easy if you extend twig.

First, create a class that will contain the extension:

<?php
 
namespace Acme\DemoBundle\Twig\Extension;

use Symfony\Component\DependencyInjection\ContainerInterface;  
use \Twig_Extension;

class VarsExtension extends Twig_Extension
{
    protected $container;
 
    public function __construct(ContainerInterface $container) 
    {
        $this->container = $container;
    }
      
    public function getName() 
    {
        return 'some.extension';
    }
    
    public function getFilters() {
        return array(
            'json_decode'   => new \Twig_Filter_Method($this, 'jsonDecode'),
        );
    }

    public function jsonDecode($str) {
        return json_decode($str);
    }
}

Then, register that class in your Services.xml file:

<service id="some_id" class="Acme\DemoBundle\Twig\Extension\VarsExtension">
        <tag name="twig.extension" />
        <argument type="service" id="service_container" />
</service>

Then, use it on your twig templates:

{% set obj = form_label(category) | json_decode %}