Shared via Rust Playground

playground.rs

const PLF: &'static &'static str = &"\n";

struct LfIter<I> where I: Iterator {
    iter: I,
    lf_every: u32,
    items: u32
}

impl<I> LfIter<I> where I: Iterator {
    fn new(iter: I, lf_every: u32) -> LfIter<I> {
        LfIter {
            iter: iter,
            lf_every: lf_every,
            items: 0
        }
    }
}

impl<'i, I> Iterator for LfIter<I> where I: Iterator<Item=&'i &'i str> {
    type Item = &'i &'i str;
    
    fn next(&mut self) -> Option<Self::Item> {
        if self.items >= self.lf_every {
            self.items = 0;
            Some(PLF)
        } else {
            self.items = self.items + 1;
            self.iter.next()
        }
    }
}

fn main() {
    let d = ["A", "B", "C", "D", "E", "F", "G"];

    let lf_iter =  LfIter::new(d.iter(), 3);
    for l in lf_iter {
        print!("{}", l);
    }
}