How can I inject callable code into the Symfon2 Dependency Injection Container container service

Given the following class definition

class CacheSubscriber implements SubscriberInterface
{
    public function __construct(
        CacheStorageInterface $cache,
        callable $canCache
    ) {
        $this->storage = $cache;
        $this->canCache = $canCache;
    }

      

        
        
        
      

    

I want to define this class as a service in Symfony2 DIC.

Although it is relatively clear what to do with the first argument

<service id="nsp_generic.guzzle.subscriber.cache" class="GuzzleHttp\Subscriber\Cache\CacheSubscriber">
    <argument type="service" id="nsp_generic.redis.cache"/>
    <!-- ??? -->
</service>

      

        
        
        
      

    

How do I define and introduce the second argument?

UPDATE

User meckhardt did it in the right direction.

Helper class

<?php

namespace Nsp\GenericBundle\Service\Cache;

class CacheConfig {
    public static function canCache() {
        return true;
    }
}

      

        
        
        
      

    

Denial of service

<service id="nsp_generic.guzzle.subscriber.cache" class="GuzzleHttp\Subscriber\Cache\CacheSubscriber">
    <argument type="service" id="nsp_generic.guzzle.subscriber.cache.storage"/>
    <argument type="collection">
        <argument>Nsp\GenericBundle\Service\Cache\CacheConfig</argument>
        <argument>canCache</argument>
    </argument>
</service>

      

        
        
        
      

    

Thanks Martin!