[eklitzke]

This is incorrect. For one thing, you're going to need to overload all the operators that mutate the integer in place, e.g. operator++, operator +=, operator -=, operator *=, shifts, etc. And those checks can be quite expensive. For example, your code is probably littered with for loops that are implemented using operator++ or operator+=, and that means on every loop iteration you need to check for overflow, which is expensive if the loop body is simple. GCC and Clang already implement -ftrapv which does something similar (it adds compiler checks at all places where signed integers can overflow and trap if overflow occurs). I've used -ftrapv in debug builds but for most programs you don't want it in non-debug builds because the overhead is too high.

[jeffffff]

the "if constexpr" makes sure the checks only happen in debug mode. you'd definitely want to turn the checks off for release builds.