#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(iter_map_windows)]
fn main() {
    let strings = "abcd"
        .chars()
        .map_windows(|[x, y]| format!("{}+{}", x, y))
        .collect::<Vec<String>>();
    assert_eq!(strings, vec!["a+b", "b+c", "c+d"]);
}