I read through the thread (which was a grind, I don't recommend it - there were many good arguments made, and many cases of RMS telling people that they were pressuring him, insulting him, or did not understand the point of free software) and I was sorely disappointed that no one just bought up constexpr.

constexpr is to a first approximation a C++ equivalent to rust's macros. Being C++ it is exciting, and basically requires a correct C++ compiler to include a correct C++ interpreter.