Inside the body of a consteval function, if you make a call to a non-constexpr function, you get a compiler warning.

Also if you were to invoke 'optional::operator*' before invoking 'optional::has_value', you might get a warning (e.g. from cppcheck).

To cut down on warnings, and to ensure that the function actually never gets invoked -- not even in a consteval context at compile time -- it would be better to tell the compiler (and also tell cppcheck) that the function is [[unevaluated]]. And if someone tries to take its address or invoke it, I would like this to be an error rather than a warning.