message: added missing method impl
diff: @@ -313,6 +313,11 @@ void string_subscription::on_update(jalson::json_object options,
  //======================================================================
  +list_model::internal_impl list_model::value() const
  +{
  + std::lock_guard<std::mutex> guard(m_value_mutex);
  + return m_value;
  +}
  void list_model::reset(internal_impl value)
  {
  std::lock(m_publishers_mutex, m_value_mutex);
  