trait Avg {
    fn average(self) -> f64;
}

impl<'a, I, T, E> Avg for I
    where
        I: IntoIterator<Item=&'a T, IntoIter=E>,
        T: Into<u64> + Copy + 'a,
        E: ExactSizeIterator<Item=&'a T>,
{
    fn average(self) -> f64 {
        let mut sum: u64 = 0;
        let iter = self.into_iter();
        let count = iter.len();
        for num in iter {
            sum += Into::<u64>::into(*num);
        }
        sum as f64 / count as f64
    }
}

fn main() {
    let v = vec![1u32, 2, 3];
    dbg!(v.average());
    dbg!([2u32, 3, 5, 8].average());
    dbg!(v);
}