Constant style_traits::arc_slice::ARC_SLICE_CANARY

const ARC_SLICE_CANARY: u64 = 0xf3f3f3f3f3f3f3f3;

A canary that we stash in ArcSlices.

Given we cannot use a zero-sized-type for the header, since well, C++ doesn’t have zsts, and we want to use cbindgen for this type, we may as well assert some sanity at runtime.

We use an u64, to guarantee that we can use a single singleton for every empty slice, even if the types they hold are aligned differently.