Regarding Dependencies

[NguyenDuyDuc]

Hi,

Following the training documents, I see when we create a new package we add dependencies like:

ros2 pkg create --build-type ament_python movement_pkg --dependencies rclpy custom_interfaces std_msgs geometry_msgs sensor_msgs

But I still use custom_interfaces, geometry_msgs without adding in dependencies.

So which way is right? adding or no add?

Thanks

[girishkumar.kannan]

Hi @NguyenDuyDuc ,

It is always best to add all the package dependencies either during creating of the package or after creating the package.

I have noticed at several times that in Python, if you declare a dependency or not, Python scripts somehow import them and use them. But if you try to do the same with a ament_cmake package with C++ scripts, then you will be forced to add the dependency package into CMakeLists.txt and package.xml.

So, by default, ament_cmake packages enforce you to add the dependencies. So as a good practice, it is always best to add all the dependencies to your ROS2 package, either during creation or post-creation of your package.

I hope this clarified your doubt. Always make it a practice to add all the dependencies to a package, irrespective of whatever type of package you are creating - that is either ament_python or ament_cmake.

Regards,
Girish

[NguyenDuyDuc]

Hi @girishkumar.kannan

If I add later, which command will I add with packages in package.xml?

add dependencies as same as the command rclpy but change the package name?

[girishkumar.kannan]

Hi @NguyenDuyDuc ,

If you want to add dependencies later you must add the exact package name of the dependency into package.xml.

For example, your are adding custom_interfaces package that you created, then you would add it into the package.xml with the following line:

<depend>custom_interfaces</depend>

There is no command that will add a dependency into your ROS2 package’s package.xml file. You have to do that manually by yourself, carefully and correctly!

Regards,
Girish

[bayodesegun]

Let me add here that adding during package creation will save you some time, effort and the occasional bugs that result from manually editing package.xml and CMakeLists.txt.