Cache/RequestLastModifiedCache.php
public function getLastModified(Request $request)
    {
        $minModified          = $this->getLastMinModifiedDate();
        $optionalLastModified = Option::fromValue($this->cache->fetch($this->getCacheKeyRequest(sha1($request->getUri()), 'lastmodified')), false);
        if ($optionalLastModified->isEmpty()) {
            return $minModified;
        }
        return max($minModified, new \DateTime($optionalLastModified->get()));
    }
public function getLastModified(Request $request)
    {
        $minModified          = $this->getLastMinModifiedDate();
        $optionalLastModified = Option::fromValue($this->cache->fetch($this->getCacheKeyRequest(sha1($request->getUri()), 'lastmodified')), false);
        if ($optionalLastModified->isEmpty()) {
            return $minModified;
        }
        return max($minModified, new \DateTime($optionalLastModified->get()));
    }
Returns the last modified date for a request.

@param Request $request

@return \DateTime