Macro cbor_via 

macro_rules! cbor_via {
    ($t:ty => $u:ty: |$x:pat| -> $xx:expr, |$y:pat| -> $yy:expr) => { ... };
    ($t:ty => $u:ty: INTO, $($rest:tt)*) => { ... };
    ($t:ty => $u:ty: |$x:ident| -> $xx:expr, FROM) => { ... };
    ($t:ty => $u:ty) => { ... };
}