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// run-pass
fn pairwise_sub<T:DoubleEndedIterator<Item=isize>>(mut t: T) -> isize {
let mut result = 0;
loop {
let front = t.next();
let back = t.next_back();
match (front, back) {
(Some(f), Some(b)) => { result += b - f; }
_ => { return result; }
}
}
}
fn main() {
let v = vec![1, 2, 3, 4, 5, 6];
let r = pairwise_sub(v.into_iter());
assert_eq!(r, 9);
}
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