ROS2 string repr of parameter within launch file

edit

It's automatically evaluated in the launch phase, so generally, you don't have to care about it.

If you'd like to print the value for debugging, you can use OpaqueFunction.
Related: https://answers.ros.org/question/3226...

I put a minimal example here.

# false
$ ros2 launch sample.launch.py use_sim_time:=false
use_sim_time: false

$ ros2 param get /publisher use_sim_time 
Boolean value is: False

# true
$ ros2 launch sample.launch.py use_sim_time:=true
use_sim_time: true

$ ros2 param get /publisher use_sim_time 
Boolean value is: True

The launch file is:

from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument, OpaqueFunction
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node, SetParameter


def launch_setup(context, *args, **kwargs):
    use_sim_time = LaunchConfiguration("use_sim_time")
    print(f"use_sim_time: {use_sim_time.perform(context)}")
    set_use_sim_time = SetParameter(name="use_sim_time", value=use_sim_time)

    node = Node(
        package="examples_rclcpp_minimal_publisher",
        executable="publisher_lambda",
        name="publisher",
    )

    return [
        set_use_sim_time,
        node,
    ]


def generate_launch_description():
    return LaunchDescription(
        [
            DeclareLaunchArgument("use_sim_time", default_value="false"),
            OpaqueFunction(function=launch_setup),
        ]
    )