Function iter

publication/code/chapter04/stack.rs:144–158

()

    }

    fn iter() {
        let mut s = Stack::new();
        s.push(1); s.push(2); s.push(3);

        let sum1 = s.iter().sum::<i32>();
        let mut addend = 0;
        for item in s.iter_mut() {
            *item += 1;
            addend += 1;
        }

        let sum2 = s.iter().sum::<i32>();
        println!("{sum1} + {addend} = {sum2}");
        assert_eq!(9, s.into_iter().sum::<i32>());
    }
}