public function set($active_ctx, $local_ctx, $result) {
    if(count($this->order) === $this->size) {
      $entry = array_shift($this->order);
      unset($this->cache->{$entry->activeCtx}->{$entry->localCtx});
    }
    $key1 = serialize($active_ctx);
    $key2 = serialize($local_ctx);
    $this->order[] = (object)array(
      'activeCtx' => $key1, 'localCtx' => $key2);
    if(!property_exists($this->cache, $key1)) {
      $this->cache->{$key1} = new stdClass();
    }
    $this->cache->{$key1}->{$key2} = JsonLdProcessor::copy($result);
  }