Comment by errnoh

Possibly that's mostly out of familiarity with the language? The only thing in your example that does things in-place (and thus looks out-of-place) is Sort(), but that's the way I'd at least expect it to work? If you take that away from the list all of them behave similarly to each other and return the modified slice:

    slices.Compact(s)       // modified slice in the return value is ignored
    s  = slices.Compact(s)  // s now points to the new changed slice
    s := slices.Compact(s)  // s already exists, this is not valid Go syntax.
    slices.Delete(s, …)     // modified slice in the return value is ignored
    s = slices.Delete(s, …) // s now points to the new changed slice

EDIT: Would prefer people not to downvote actual discussion. In this case there were was indeed good argument made on the reply that these also modify the underlying slice, but it's not like I was being rude in the comment.