;; ZII fills an omitted field with all-bytes-zero, and a zeroed function value ;; is a null pointer — the one kind of zero that is not a value the type can ;; have. Every other type's zero is one: 0, false, an empty slice, None, a ;; union's first case. So it is refused where the field is written rather than ;; left to crash at the call, and the same rule covers a global, a fixed ;; array's element and (zeroed). (defstruct Ops [run (Fn [i32] i32)]) (defn main [] i32 0)