append is the opposite of magic. it's exposing the details of a realloc when 99% of the time you want to keep the same binding. That's probably also why map doesn't have an equivalent; in the case of hash tables it's more like 99.999%.
You cannot write the append function in pre-go 1.18. That is what I mean by magic. The reason it's given to you because it would be painful to build a function like append for every slice type. That's also why it gets to have blessed nil properties.
Well, you could, using unsafe. But you also couldn't write the index operator (without unsafe), and I don't think anyone would call that "magic". And in either case that has nothing to do with its treatment of nil.
It would be more magic if it somehow updated a hidden pointer, like maps do. (And this has also been my experience teaching Go, people grasp quickly that slice length/cap is immutable but often forget that non-nil maps are mutable and always "by reference".)
