fn generate_default_protocol_slot(
    cls: &Type,
    method: &mut ImplItemFn,
    slot: &SlotDef,
    ctx: &Ctx,
) -> Result<MethodAndSlotDef>fn generate_default_protocol_slot(
    cls: &Type,
    method: &mut ImplItemFn,
    slot: &SlotDef,
    ctx: &Ctx,
) -> Result<MethodAndSlotDef>