As for linking to the concrete filter plugins, I'm not sure if class_loader_hide_library_symbols is not needed in CMake. It is used e.g. in pcl_ros, and there's a half-answered question about its necessity for dynamically loaded plugins: ros-perception/perception_pcl#9 . If this CMake macro were used, then no changes to either API or ABI of the concrete plugins could break any downstream code.

There's another design option - making InplaceFilterBase and InplaceMultiChannelFilterBase classes just mixins without any base class. That would allow "tagging" inplace even downstream classes for which it's not that easy to change the base class.

Thanks for contributing this. As it's an API changing update. Although it likely won't effect people we'll want to target this for a future distribution to be sure not to disrupt existing users and stay stable. So we'll want to retarget this to the rolling distribution.

Is there a new ROS 1 distro coming?

Friendly ping. If you're concerned about breaking the ABI/API, I can just rename the existing filters and create their inplace duplicates. Not really good from the code point of view, but it would do the job.

There's not a new rosdistro coming in ROS 1. To land in noetic the creating new parallel classes would be a way to support a backport.

There is in ROS 2 which is being developed off the ros2 branch. If you'd like to target this for future versions that could be useful.

Okay, I've made the PR ABI compatible. The filters are now duplicated, but fortunately code can be shared.

I also added a non-virtual update(T&) function to FilterBase that dispatches based on RTTI to the correct override. It is a convenience function. It doesn't need to be there if it's not desired.

Once the approach is approved, I'll finish documentation and tests.

Thank you for the PR!

Unfortunately I don't think we should merge this one.

ROS Noetic will reach end-of-life on May 31st, 2025. Every change comes with a risk of introducing regressions, and there isn't much time left to fix them. I'm closing pull requests that add features so that the remaining time is allocated towards bug fixes and compatibility with newer Ubuntu distros.