fn main() {
    let v1 = vec![String::from("foo"), String::from("bar")];
    let v2 = vec![String::from("baz"), String::from("qux")];

    let it = v1.iter().map(|s1| v2.iter().map(|s2| (s1, s2))).flat_map(|x| x);

    for item in it {
        let (s1, s2) = item;
        println!("{} {}", s1, s2)
    }
}