3 fn pairwise_sub(mut t: Box<dyn DoubleEndedIterator<Item=isize>>) -> isize {
7 let back = t.next_back();
9 (Some(f), Some(b)) => { result += b - f; }
10 _ => { return result; }
16 let v = vec![1, 2, 3, 4, 5, 6];
17 let r = pairwise_sub(Box::new(v.into_iter()));