use std::ops::Add;

struct RangeFinder<'a, T: 'a> {
    index: usize,
    length: usize,
    arr: &'a [T],
}

impl<'a, T> Iterator for RangeFinder<'a, T> where T: PartialEq + Add<u8, Output=T> + Copy {
    type Item = (T,  Option<T>);
    fn next(&mut self) -> Option<Self::Item> {
        if self.index == self.length {
            return None;
        }
        let lo = self.index;
        while self.index < self.length - 1 && self.arr[self.index + 1] == self.arr[self.index] + 1 {
            self.index += 1
        }
        let hi = self.index;
        self.index += 1;
        if hi - lo > 1 {
            Some((self.arr[lo], Some(self.arr[hi])))
        } else {
            if hi - lo == 1 {
                self.index -= 1
            }
            Some((self.arr[lo], None))
        }
    }
}

impl<'a, T> RangeFinder<'a, T> {
    fn new(a: &'a [T]) -> Self {
        RangeFinder {
            index: 0,
            arr: a,
            length: a.len(),
        }
    }
}

fn main() {
    let n = [0,1,2,3];

    for (i, (lo, hi)) in RangeFinder::new(&n).enumerate() {
        if i > 0 {print!(", ")}
        print!("{}", lo);
        if hi.is_some() {print!("-{}", hi.unwrap())}
    }
    println!("");
}