I hope your comment wasn't intended to be as hostile as it reads to me, but I do wonder what your experience was exactly, because there might be a misinterpreta

I hope your comment wasn't intended to be as hostile as it reads to me, but I do wonder what your experience was exactly, because there might be a misinterpretation. From a technical standpoint, using const_cast to modify a constant is Undefined Behavior. This was explicitly specified that way to make constants inlineable by the compiler. Every compiler that I've ever used does this, it's a trivial but very effective optimization. Proof by Godbolt: https://godbolt.org/z/djEdvee4s https://godbolt.org/z/djEdvee4s Observe how GCC completely eliminates the contents of undefined_mutate_modulus (which it's allowed to -- UB means it can do anything with that function, and it chooses the simplest possible thing) rather than de-optimizing mod4_const like you suggested. Compilers are smart.