> Are compilers required to evaluate constexpr expressions at compile time, where possible? No. But C++20 adds consteval, which does carry that requirement: h

> Are compilers required to evaluate constexpr expressions at compile time, where possible? No. But C++20 adds consteval, which does carry that requirement: https://www.modernescpp.com/index.php/c-20-consteval-and-constinit https://www.modernescpp.com/index.php/c-20-consteval-and-con... Well, sort of. It has to produce a constant expression, and in practice the way to do that is to evaluate it at compile-time. But under the as-if rule, a compiler can do what it likes, up to and including producing a binary containing your source code and a copy of gcc, and compiling your entire program when you run it.