map is lazy that can cause problems

---

examples/vectors/map1/src/main.rs

fn main() {
    let chars = vec!['a', 'b', 'c'];
    let mut c = 0;
    let pairs = chars.into_iter().map(|letter| {
        c += 1;
        (letter, c)
    });
    for pair in pairs {
        println!("{pair:?}");
    }
}

('a', 1)
('b', 2)
('c', 3)

examples/vectors/map2/src/main.rs

fn main() {
    let chars = vec!['a', 'b', 'c'];
    let mut c = 0;
    let pairs = chars.into_iter().rev().map(|letter| {
        c += 1;
        (letter, c)
    });
    for pair in pairs {
        println!("{pair:?}");
    }
}

('c', 1)
('b', 2)
('a', 3)

examples/vectors/map3/src/main.rs

// However this is also the same
fn main() {
    let chars = vec!['a', 'b', 'c'];
    let mut c = 0;
    let pairs = chars
        .into_iter()
        .map(|letter| {
            c += 1;
            (letter, c)
        })
        .rev();
    for pair in pairs {
        println!("{pair:?}");
    }
}

('c', 1)
('b', 2)
('a', 3)