The best part is, there's a subtle API breakage here: the returned *Rule is now a reference to an element of the []Rule, so if the caller was previously modifyi

The best part is, there's a subtle API breakage here: the returned *Rule is now a reference to an element of the []Rule, so if the caller was previously modifying the returned value it'll change the slice. It's debatable what API guarantees existed around this though; most of the time this would be unspecified.