Macro return_mode_ty 

macro_rules! return_mode_ty {
    (
        (copy, $maybe_backdate:ident, $maybe_default:ident),
        $db_lt:lifetime,
        $field_ty:ty
    ) => { ... };
    (
        (clone, $maybe_backdate:ident, $maybe_default:ident),
        $db_lt:lifetime,
        $field_ty:ty
    ) => { ... };
    (
        (ref, $maybe_backdate:ident, $maybe_default:ident),
        $db_lt:lifetime,
        $field_ty:ty
    ) => { ... };
    (
        (deref, $maybe_backdate:ident, $maybe_default:ident),
        $db_lt:lifetime,
        $field_ty:ty
    ) => { ... };
    (
        (as_ref, $maybe_backdate:ident, $maybe_default:ident),
        $db_lt:lifetime,
        $field_ty:ty
    ) => { ... };
    (
        (as_deref, $maybe_backdate:ident, $maybe_default:ident),
        $db_lt:lifetime,
        $field_ty:ty
    ) => { ... };
}