How to pass value from service to twig.global.var in symfony2?

Question

symfony

I want to set up a global array to manipulate currency rates in all twig templates.
Configuration: config.yml

twig:
    #...
    globals:
            rate: '@crbr.currency_rate'

Registering a service

crbr.currency_rate:
        class: CrbrBundle\Service\CurrencyRate
        arguments:
            - '@redcode.currency.rate.converter'

Sevris itself

<?php
namespace CrbrBundle\Service;

use Doctrine\ORM\EntityManager;

class CurrencyRate
{
    public function __construct($currency)
    {
        $this->$converter = $currency;
    }
    public function getRate()
    {
        $rate = array();
        $currencyDiff = $this->container->getParameter('currencyDiff');
        $converter = $this->get('redcode.currency.rate.converter');
        $rate['usd'] = $this->convert('USD', 'RUB', 1) + $currencyDiff;
        $rate['jpy'] = $this->convert('JPY', 'RUB', 1) * 100 + $currencyDiff;
        return $rate;
    }

}

Actually, the question is how in my
globals setup config:
rate: Is it correct to pass the rate value by calling my service with the necessary action?

Answer 1

I want to set up a global array to manipulate currency rates in all twig templates.

Or maybe you don't want to?
In any case, it's better to look towards extensions for twig and registering your function.