Every C++ compiler still in use will not even try to open a header-guarded or #pragma once file it has already seen. Anybody trying to optimize on top of that

Every C++ compiler still in use will not even try to open a header-guarded or #pragma once file it has already seen. Anybody trying to optimize on top of that is engaged in foolish superstition. (If you are still using Sun's pre-Standard compiler, you are not reading this. I think even Bloomberg has abandoned that.)