Mastering Rust - Second Edition

Using combinators

Using the map method is simple:

// using_map.rsfn get_nth(items: &Vec<usize>, nth: usize) -> Option<usize> {    if nth < items.len() {        Some(items[nth])    } else {        None    }}fn double(val: usize) -> usize {    val * val}fn main() {    let items = vec![7, 6, 4, 3, 5, 3, 10, 3, 2, 4];    println!("{}", items.len());    let doubled = get_nth(&items, 4).map(double);    println!("{:?}", doubled);}

In the preceding code, we have a method called get_nth that gives us the nth element from Vec<usize> and returns None if it couldn't find one. We then have a use case where we want to double the value. We can use the map method on the return value of get_nth, passing in the double function we defined previously. Alternatively, we could have provided a closure ...