Compilers diagnose when functions can't be proved to return, and I wouldn't work on a codebase without this diagnostic enabled as an error. Is there a valid reason to keep this UB around?
How does one write an assert-type macro which, when it is disabled, still prevents this type of warning/error? Because people do write:
my_assert(false);
to mean abort in debug mode, take my chances in release mode.
I don’t think I understand what you’re asking... but it sounds like
#ifdef _DEBUG
#define YOLO() abort()
#else
#define YOLO() std::unreachable() // or __builtin_unreachable()
That looks right to me.
JF,
(1) You originally mentioned "[[noreturn]]" in the same breath with "unreachable," which is confusing to me. Suppose I write a function `f1` declared `[[noreturn]]`, which "seemingly falls off the end"; say, `void g(); [[noreturn]] int f1() { g(); }` — Does f's code clearly indicate my intent that "I know g() is non-returning, so please don't warn here," or does f's code suggest to the compiler that I've written a bug?
Would you make it so that a conforming compiler required to diagnose this code as ill-formed? Or required not to diagnose it?
(2) How do we standardize the idea that the compiler should be able to do control flow analysis here? I mean, if we have, like, `int f2() { while (true) { if (rand()) return 42; } }`, is a conforming compiler supposed to be smart enough to see the end of the function is unreachable? Or what if it's, like,
int f3(bool b) {
if (b) { return 42; }
if (!b) { abort(); } // or std::unreachable(), your choice
}
Would you make it so that a conforming compiler required to diagnose this code as ill-formed? Or required not to diagnose it?
(3) Alternatively, are you proposing that a conforming compiler should be forced to insert a call to `std::terminate()` at the bottom of any function it can't prove isn't reached? (That would be nicely consistent with the big oops C++ made with `noexcept`.)
Basically, "needs a paper, needs Tony Tables."
my $.02,
–Arthur