rep.rs

#![allow(unused)]
#![feature(macro_at_most_once_rep)]

macro_rules! opt {
    (pub $($n:ident $( ($t:ty) )? ,)+) => {
        enum Foo {
            $( $n $( ($t) )?, )+
        }
    }
}

opt!{pub
    A,
    B(u32),
    C(i32),
    D,
}

fn main() {
    let f = Foo::A;
}