Seems like its in C29, but who knows. I've waited since 2009 for just about anything
C29 is shaping up to be some quality of life changes. And it looks like clang has a lot of it implemented already. GCC seems to be implementing some of them. `countof(thing)` seems handy so I don't have to define some constant and use them in both places.
Not having to write
#define len(x) sizeof(x) / sizeof(*x)
Is arguably the feature I've waited for for 20 years