Example:

Build the node

 mkdir colcon_ws
 mkdir colcon_ws/src
 cd colcon_ws/src
 git clone https://github.com/picknikrobotics/generate_parameter_library.git
 cd ..
 colcon build

Run the node

source install/setup.bash
ros2 run generate_parameter_library_example test_node --ros-args --params-file src/generate_parameter_library/example/config/implementation.yaml

You should see an output like this: [INFO] [1656018676.015816509] [admittance_controller]: Control frame is: 'ee_link'

ROS 2 CLI

Run the following:

ros2 param list

You should see:

  /admittance_controller:
  admittance.damping_ratio
  admittance.mass
  admittance.selected_axes
  admittance.stiffness
  chainable_command_interfaces
  command_interfaces
  control.frame.external
  control.frame.id
  enable_parameter_update_without_reactivation
  fixed_world_frame.frame.external
  fixed_world_frame.frame.id
  ft_sensor.frame.external
  ft_sensor.frame.id
  ft_sensor.name
  gravity_compensation.CoG.force
  gravity_compensation.CoG.pos
  gravity_compensation.frame.external
  gravity_compensation.frame.id
  joints
  kinematics.base
  kinematics.plugin_name
  kinematics.tip
  qos_overrides./parameter_events.publisher.depth
  qos_overrides./parameter_events.publisher.durability
  qos_overrides./parameter_events.publisher.history
  qos_overrides./parameter_events.publisher.reliability
  state_interfaces
  use_sim_time

All parameter are automatically declared and callbacks are setup by default. You can set a parameter by typing:

ros2 param set /admittance_controller control.frame.id new_frame

You should see:

[INFO] [1656019001.515820371] [admittance_controller]: Control frame is: 'new_frame'

Congratulations, you updated the parameter!

If you try to set a parameter that is read only, you will get an error. Running the following

ros2 param set /admittance_controller joints ["joint_new"]

will result in the error

Setting parameter failed: parameter 'joints' cannot be set because it is read-only

Running the following

ros2 param describe /admittance_controller admittance.damping_ratio

will show a parameter's description

 Parameter name: admittance.damping_ratio
  Type: double array
  Description: specifies damping ratio values for x, y, z, rx, ry, and rz used in the admittance calculation. The values are calculated as damping can be used instead: zeta = D / (2 * sqrt( M * S ))
  Constraints:
    Min value: 0.1
    Max value: 10.0

If you try to set a value out of the specified bounds,

ros2 param set /admittance_controller admittance.damping_ratio [-10.0,-10.0,-10.0,-10.0,-10.0,-10.0]

you will get the error

Setting parameter failed: Invalid value for parameter admittance.damping_ratio. Value not within required bounds.

If you try to set a vector parameter with the wrong length,

ros2 param set /admittance_controller admittance.damping_ratio [1.0,1.0,1.0]

you will get the error

Setting parameter failed: Invalid size for vector parameter admittance.damping_ratio. Expected 6 got 3

If you try to load a yaml file with missing required parameters

ros2 run generate_parameter_library_example test_node --ros-args --params-file src/generate_parameter_library/example/config/missing_required.yaml

you will get the error

terminate called after throwing an instance of 'rclcpp::exceptions::ParameterUninitializedException'
  what():  parameter 'command_interfaces' is not initialized
[ros2run]: Aborted

Changelog for package generate_parameter_library_example

0.2.3 (2022-08-05)

0.2.2 (2022-08-03)

0.2.1 (2022-08-02)

• Fix scientific notation (#46)
• Contributors: Paul Gesel

0.2.0 (2022-08-01)

• Create stack allocated struct (#45)
• Fixed length arrays (#44)
• Fixed size string no default bug (#43)
• static OK to fix ODR errors (#41)
• Change package name (#40)
• parameter validators interface library (#32)
• Validate fixed length Strings (#33)
• Fixed size strings (#29)
• Contributors: Paul Gesel, Tyler Weaver

0.1.0 (2022-07-27)

• Example usage of generate_parameter_library.
• Contributors: Paul Gesel, Tyler Weaver