Macro impl_altraw_from_data_generic 

macro_rules! impl_altraw_from_data_generic {
    ({$($gen:tt)*} $ty:ty {$($whr:tt)*} $(, $knob:ident)*) => { ... };
}

Generic form of impl_altraw_from_data! — see impl_altinteger_from_data_generic! for the calling convention.