It’s interesting how Zig clicked for me pretty quickly (although I have been writing it for a couple of years now). But some of the strategies of ownership and data oriented design I picked up writing JavaScript. Sometimes returning a new slice and sometimes returning the same slice is a problem for memory cleanup, but I wouldn’t do it even in JavaScript because it makes it difficult for the caller to know whether they can mutate the slice safely.

I suspect that there’s a way to write this algorithm without allocating a temporary buffer for each iteration. If I’m right that it’s just intersecting N sets, then I would start by making a copy of the first set, and on each iteration, removing items that don’t appear in the new set. I suspect the author is frustrated that Zig doesn’t have an intersect primitive for arrays, but usually when the Zig standard library doesn’t have something, it’s intentionally pushing you to a different algorithm.