Extending twig

Remarks#

Twig already has some built-in filters and functions, but what if the built-in features are lacking or you have to access some default PHP functions in a template

Adding custom filters/functions

Here are some example on how to add new filters/functions to twig,
the synax for adding Twig_Functions are the same as the Twig_Filter ones, just change the keywords accordingly

<?php
   $twig = new Twig_Environment($loader);

   /* You can chain a global function */
   $twig->addFilter(new Twig_SimpleFilter('floor', 'floor'));
   
   /* You can specify a custom function */
   $twig->addFilter(new Twig_SimpleFilter('money', function($value, $currency, $prefix = false, $decimals = 2, $dec_point = "." , $thousands_sep = ",") {
       $value = number_format($value, $decimals, $dec_point, $thousands_sep);
       if ($prefix) return $currency.' '.$value;
       return $value.' '.$prefix;
   });

   /* You can chain an object's method */
   $twig->addFilter(new Twig_SimpleFilter('foo_bar', array($foo, 'bar')));

Creating a Twig_Extension

You can group all your custom functions/filters/tests/… inside a custom Twig_Extension class:

ProjectTwigExtension

class ProjectTwigExtension extends Twig_Extension {

    public function getFunctions() {
        return array(
            new Twig_SimpleFunction('twig_function_name', array($this, 'getTwigFunctionName')),
            new Twig_SimpleFunction('twig_function_foo', array($this, 'getTwigFunctionFoo')),            
        );



    }
    public function getFilters() {
        return array(
            new Twig_SimpleFilter('twig_filter_name' , array($this, 'getTwigFilterName')),
            new Twig_SimpleFilter('twig_filter_foo' , array($this, 'getTwigFilterFoo')),
        );
    }
    
    public function getName() {
        return 'ProjectTwigExtension';
    }        
}

Register extension in twig

$twig = new Twig_Environment($loader);
$twig->addExtension(new ProjectTwigExtension());

More options can be found on the official docs

Simple Date of Birth to age filter

How to …

1 - use twig extension class that extends

use \Twig_Extension

class dobToAge extends \Twig_Extension {

2 - Add the appropriate filter by overriding getFilters() method

 public function getFilters() {
        return array(
            'age' => new \Twig_Filter_Method($this, 'getAge'),
        );
 }

3 - Add some logic to get the age of a given Date of Birth

 public function getAge($date) 
     {
        if (!$date instanceof \DateTime) {
        // turn $date into a valid \DateTime object or let return
        return null;
         }

     $referenceDate = date('01-01-Y');
     $referenceDateTimeObject = new \DateTime($referenceDate);
     $diff = $referenceDateTimeObject->diff($date);
     return $diff->y;
    }
}

Then, call your filter as follow,

{{ yourDateOfBirthInstance | age }}