constexpr and endianness

Question

A common question that comes up from time to time in the world of C++ programming is compile-time determination of endianness. Usually this is done with barely portable #if

Answer 1

If your goal is to insure that the compiler optimizes little_endian() into a constant true or false at compile-time, without any of its contents winding up in the executable or being executed at runtime, and only generating code from the "correct" one of your two Foo templates, I fear you're in for a disappointment.

I also am not a language lawyer, but it looks to me like constexpr is like inline or register: a keyword that alerts the compiler writer to the presence of a potential optimization. Then it's up to the compiler writer whether or not to take advantage of that. Language specs typically mandate behaviors, not optimizations.

Also, have you actually tried this on a variety of C++0x complaint compilers to see what happens? I would guess most of them would choke on your dual templates, since they won't be able to figure out which one to use if invoked with false.