Function iter_set::cmp_by

pub fn cmp_by<T, L, R, F>(a: L, b: R, cmp: F) -> Option<Ordering> where
    L: IntoIterator<Item = T>,
    R: IntoIterator<Item = T>,
    F: FnMut(&mut T, &mut T) -> Ordering, 

Compare two sets represented by sorted, deduplicated iterators, using a comparator function.

See cmp.