I have had to reimplement lots of stuff that are given for-free in any other, higher-level (not necessarily high-level) language. This includes, for example, a "class" to deal with dynamic strings, another one for dynamic linked lists and iterators, a way to propagate errors until the point where they can be managed... and I have spent quite a bit of time debugging crashes due to memory management bugs, something that I rarely encountered in the C++ version.
However, the new interface is, I believe, quite neat. This is not because of the language per se, but because the C++ interface has grown "incorrectly". It was the first code in the project and it shows. The C version has been written from the ground up with all the requirements known beforehand, so it is cleaner. This will surely help in cleaning up the C++ version later on, which cannot die anyway.
The code for this interface is in a new branch, org.NetBSD.atf.src.c, and will hopefully make it to ATF 0.5: it still lacks a lot of features, hence why it is not on mainline. Ah, the joys of a distributed VCS: I have been able to develop this experiment locally and privately until it was decent enough to be published, and now it is online with all history available!
From now on C++ use will be restricted to the ATF tools inside ATF itself, and to those users who want to use it in their projects. Test cases will be written using the C library except for those that unit-test C++ code.