unique_consts.rs

macro_rules! make_encoding_ids_rec {
    ($count:expr) => {};
    ($count:expr, $encoding:ident $($tts:tt)*) => {
        pub const $encoding: u16 = $count;
        make_encoding_ids_rec!(($count+1u16) $($tts)*);
    }
}

macro_rules! make_encoding_ids {
    ($($encodings:ident),*) => {
        make_encoding_ids_rec!(1u16 $(, $encodings)*);
    };
}

make_encoding_ids! {
      FIRST
    , SECOND
    , THIRD
}