The special-casing of index access in generic dispatch functions could use a better interface, ideally be more general. Skipping the actual property allocation for indexed access seems desirable for other objects too. With that, accepting all possible indexes should be as simple as returning maximum possible length from `_get_length` implementation. Adding a function to `builtin_info_t` that would return a property descriptor for indexed properties (on per-class basis, possibly without relying on `dispex_prop_t`) should allow proper handling of defining/querying properties.