1. Its decltype has to fail std::is_pointer and pass std::is_pod.
2. Definition/implementation of the data struct doesn't count -> no inline structs.
3. No whitespace, typedefs or anything cheesy. Definition only -> initialization doesn't count.
4. No decltype
Ah yea, thread_local is defo legit. Not sure if extern counts as a declaration. So I guess
alignas(0) thread_localstaticconstexprconstvolatileunsignedlonglongint x = 0;
is in the lead. Althougth a const constexpr that is thread_local and volatile is a bit odd. I guess it's the ultimate way of saying "this value should never change, but if by some magic it does, keep it to 1 thread. Also despite the fact it never changes, don't cache it in a register".