len
      (Store {t.Elem().PtrTo()} dst ptr mem)))

// interface ops
(ITab (IMake itab _)) => itab
(IData (IMake _ data)) => data

(Load <t> ptr mem) && t.IsInterface() =>
  (IMake
    (Load <typ.Uintptr> ptr mem)
    (Load <typ.BytePtr>
      (OffPtr <typ.BytePtrPtr> [config.PtrSize] ptr)
      mem))
(Store dst (IMake itab data) mem) =>
  (Store {typ.BytePtr}
    (OffPtr <typ.BytePtrPtr> [config.PtrSize] dst)