Macro impl_altinteger_from_data_generic 

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

Generic form of impl_altinteger_from_data!: accepts an optional generic parameter list and where-clause ({T, U} Foo<T, U> {T: Bound, ..}) so it can target struct Foo<T> { .. } types, not just concrete/monomorphic ones. The non-generic macro above forwards here with empty {} brackets so there is exactly one emission body for both call shapes.