Specifying parameter type in ROS2 XML launch file

Question

I am trying to declare two string parameters vid and pid for a serial communication node in ROS2. However, when I use the following launch file to pass my parameters:

<launch>
  <node pkg="serial" exec="serial">
    <param name="vid" type="str" value="0483"/>
    <param name="pid" type="str" value="5740"/>
  </node>
</launch>

I got the following error:

[serial-1] terminate called after throwing an instance of 'rclcpp::exceptions::InvalidParameterTypeException'
[serial-1]   what():  parameter 'vid' has invalid type: Wrong parameter type, parameter {vid} is of type {string}, setting it to {double} is not allowed.

It seems like my type specification was never respected by roslaunch.

According to the official documentation it seems like ROS2 removed support for explicit type declaration. I want to understand the rationale behind this change and find out possible alternative approaches (without moving away from xml format).

---

Update: Add C++ source code for reproducibility

class SerialNode: public rclcpp::Node {
  SerialNode(): Node("serial") {
    declare_parameter<std::string>("pid", "");
    declare_parameter<std::string>("vid", "");
    declare_parameter<int>("baud", 115200);
    const auto vid = get_parameter("vid").as_string();
    const auto pid = get_parameter("pid").as_string();
    const auto baud = get_parameter("baud").as_int();
  }
  /* irrelevant code omitted ... */
}

---

Update:

1. The python version of launch file also produces identical error.
2. I added a letter x in front of my values (i.e. x0483 and x5740 instead of 0483 and 5740), then the parameters are successfully passed as strings. I think this is a very strong proof that my code is not causing this error.

[serial-1] No serial port found for device x0483:x5740

Answer 1

Can you update your launch file like this? I think there is a problem on your XML file.

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription([
        Node(
            package='serial',  
            executable='serial',
            name='serial',
            output='screen',
            parameters=[
                {'vid': 0x0483},  # 'vid' parameter
                {'pid': 0x5740},  # 'pid' parameter
            ]
        ),
    ])