[gpderetta]

>> But implementors are not: they can bless their own span with superpowers if they want to > Except that they don’t. And we can go around in circles here

Except they do. Look at GCC code for std::complex compared to the equivalent hand rolled class: https://gcc.godbolt.org/z/nqcvhPWex . edit: note that in this case GCC is just silly with the hand rolled one, but it does show that they are treated differently.

GCC does similar things with span where the class has special annotations for reference tracking to improve warning messages.

Library vs builtin is an implementation issue, not a standardization one. But yes, we are going in circle.