hi all,

The code below seems to work well as I expected, but it doesn't.

class MyClass : public rclcpp::Node
{
public:
  MyClass()
  : Node("my_class")
  {
    subscription_ = this->create_subscription<std_msgs::msg::String>(
      "test", 10, std::bind(&MyClass::MyCallback, this, _1));
  }

private:
  rclcpp::Subscription<std_msgs::msg::String>::SharedPtr subscription_;
  void MyCallback(const std_msgs::msg::String::SharedPtr msg) const
  {
    RCLCPP_INFO(rclcpp::get_logger("MyClass"), "Subscribed : '%s'", msg->data.c_str());
  }
};


int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
/*
  // work well 
  rclcpp::executors::SingleThreadedExecutor single_exec;
  auto a = std::make_shared<MyClass>();
  single_exec.add_node(a);
  single_exec.spin();

  // work well 
  rclcpp::spin(std::make_shared<MyClass>());

*/  
  // not work
  rclcpp::executors::SingleThreadedExecutor single_exec;
  single_exec.add_node(std::make_shared<MyClass>());
  single_exec.spin();

  rclcpp::shutdown();
  return 0;
}

The MyClass is derived from rclcpp::Node, and the shared pointer is implicitly convertible to a shared pointer to rclcpp::Node. The addnode function in the executor takes a shared pointer to rclcpp::Node, so the call to addnode should succeed. However, when I run the code upper, it doesn't subscribe to the topic and can't be found on the ros2 node list command; it just blocks.

If I replace the executor code with either of the ones in the comments, it works well.