I propose to allow reinterpret_cast from pointer to integral, as well as the no-op/identity reintepret_cast in constant expressions. This particular version is useful in implementing hashcode algorithms at compile time, and to my knowledge bit_cast does not work for pointer types at compile time.
I think this is a non-starter. Consider:
const int i = 42;
constexpr int is_64_aligned(const int *p) {
return reinterpret_cast<intptr_t>(p) % 64 == 0;
}
constexpr bool x = is_64_aligned(&i);
int main(int argc, char **argv) {
bool y = is_64_aligned(argc ? &i : nullptr);
assert(x == y);
}
How is the compiler supposed to know at compile time what bits are in the runtime bit-pattern of `p`?