A trap representation is not a NaN-like sentinel value. The post also didn't discuss the updated semantics of integer operations, but I assume it just simply sh

A trap representation is not a NaN-like sentinel value. The post also didn't discuss the updated semantics of integer operations, but I assume it just simply shrinks the range of representable values by removing -2^(N-1), and operations with a resulting value that lie outside are still undefined. Having a NaN-like sentinel with is another option, with overflowing integer operations defaulting to that value instead, but that's not what is proposed here. The post does mention optional<int>, which could have the NaN-like sentinel (empty optional) by reusing the bit-pattern of the trap representation of the underlying int.