Function rank_impl_by 

fn rank_impl_by<T, C, E>(
    len: usize,
    valid: Vec<(T, u32)>,
    options: SortOptions,
    compare: C,
    eq: E,
) -> Vec<u32>
where
    C: Fn(&(T, u32), &(T, u32)) -> Ordering,
    E: Fn(&(T, u32), &(T, u32)) -> bool,