Go iota in Rust

iota.rs

macro_rules! __iotadef_recur {
    ($total:expr, $expr:expr, $t:ty, $head:ident) => {
        pub const $head: $t = const { const IOTA: $t = $total - 1; $expr };
    };
    ($total:expr, $expr:expr, $t:ty, $head:ident, $( $tail:ident ),*) => {
        pub const $head: $t = const {
            #[repr($t)]
            enum RecurCount {
                $( $tail, )*
                ____NumberElementsLeft,
            }
            const IOTA: $t = $total - RecurCount::____NumberElementsLeft as $t - 1;
            $expr
        };
        __iotadef_recur!(
            $total,
            $expr,
            $t,
            $( $tail ),*
        );
    };
}

macro_rules! iotadef {
    ($vis:vis $name:ident { $firstdef:ident : $t:ty = $expr:expr $(, $def:ident )* $(,)? }) => {
        #[allow(dead_code)]
        $vis mod $name {
            #[repr($t)]
            enum Count {
                $firstdef,
                $( $def, )*
                ____TotalNumberElements,
            }
            __iotadef_recur!(
                Count::____TotalNumberElements as $t,
                $expr,
                $t,
                $firstdef,
                $( $def ),*
            );
        }
    }
}

iotadef!(pub cenas {
    A: isize = IOTA << 1,
    B,
    C,
    D,
});

fn main() {
    println!("{}", cenas::A);
    println!("{}", cenas::B);
    println!("{}", cenas::C);
    println!("{}", cenas::D);
}