public function isFresh(ResourceInterface $resource, $timestamp)
 {
     return $resource->isFresh($timestamp);
 }
 /**
  *
  * {@inheritdoc} @api
  */
 public function addResource(ResourceInterface $resource)
 {
     $this->resources[$resource->__toString()] = $resource;
 }
 public function isFresh(ResourceInterface $resource, $timestamp)
 {
     /* @var SelfCheckingResourceInterface $resource */
     return $resource->isFresh($timestamp);
 }