doubler.rs

gistfile1.txt

struct Doubler<I: Iterator> {
    iter: I,
}

impl<I> Iterator for Doubler<I>
where
    I: Iterator,
    I::Item: std::ops::Add<Output = I::Item> + Copy,
{
    type Item = I::Item;
    fn next(&mut self) -> Option<<Self as Iterator>::Item> {
        self.iter.next().map(|x| x + x)
    }
}