What’s where [(); SIZE + Kind::EXTRA]:?

Oh no noes! Back from holiday, with Rust 1.93 I can’t validate your optimism. Each of the three A + B exprs gives me both “cannot perform const operation using A” and “cannot perform const operation using B”.

So you say something about only being stable for slices? How exactly do you mean that? And under what circumstances would those slices be optimised away, i.e. zero-cost?