Things to know before enabling HXCPP_GC_GENERATIONAL?

I would like to experiment with enabling generational GC on a Haxe project, but before doing so, I would like to know if there are any subtleties I should be aware of, given that the project has a lot of C/C++ externs (even Objective-C++ when targeting iOS).

I found @hughsando's haxe summit 2017 notes about [needing write-barrier when enabling generational GC](https://github.com/hughsando/HaxeSummit2017) but I didn't find more information about it.

Does enabling generational GC means I need to make a few changes to my extern/C++ code? If yes are there any examples/docs that can help? And is the generational GC considered _pretty stable_ or should I expect a few things to break?

Thanks in advance for any hint!

(I though this question was better here than in the community forums)