Or until something else changes, which invalidates the cache. If the current GIT commit is a far more useful information, our discussion also clarified, what possible ways could include such compile-time configuration. A generated header file or even source code file is always an option, but perhaps one wants to provide a nice constexpr interface for compile-time configuration. We generally discussed the pitfalls and possible compromises. -----Ursprüngliche Nachricht----- Von:Thiago Macieira via Std-Proposals <std-proposals_at_[hidden]> The alternative is that it is an intrinsic without preprocessor changes, in which case the output would be cached and it would hit on reuse. That in turn means you will keep getting the time of the first cache, until you clean the cache or the output expires from the cache.