Kind of. At the end of the day the compiler can do almost anything it wants outside of unrefined behavior, which isn't much of a guard rail. In reality header

Kind of. At the end of the day the compiler can do almost anything it wants outside of unrefined behavior, which isn't much of a guard rail. In reality header only libraries allow for deep inlining, the compiler may optimize very specifically to your code and usage. The situation is a bit more exaggerated with C++ because of templates, but there is some remaining gains to he had in C alone.