CG\Di\Definition\RuntimeDefinition\Cache.php

<?php
namespace CG\Di\Definition\RuntimeDefinition;

use CG\Di\Definition\RuntimeDefinition;
use Zend\Di\Definition\IntrospectionStrategy;
use Zend\Cache\Storage\StorageInterface;
use Zend\Cache\Storage\Adapter\Memory;

class Cache extends RuntimeDefinition
{
    protected $cache;
    public function __construct(
        IntrospectionStrategy $introspectionStrategy = null,
        array $explicitClasses = null,
        StorageInterface $cache = null
    ) {
        parent::__construct($introspectionStrategy = null, $explicitClasses = null);
        if (is_null($cache)) {
            return;
        }
        $this->cache = $cache;
        register_shutdown_function([$this, 'persistDefinitions']);
    }

    public function persistDefinitions()
    {
        $this->cache->setItem(
            'classes',
            array_merge(
                $this->classes,
                $this->cache->getItem('classes')
            );
        );
    }
}

index.php

<?php
$definitions = new ArrayDefinition($cache->getItem('classes'));