fn sum_all_numbers(val: u64) -> u64 {
    let mut x = val;
    let mut sum = 0;
    while x / 10 > 0 {
        sum = sum + x % 10;
        x = x / 10;
    }
    sum + x
}

struct DigitEnumerator(u64);

impl Iterator for DigitEnumerator {
    type Item = u64;

    fn next(&mut self) -> Option<u64> {
        let result = self.0 % 10;
        if result == 0 {
            return None;
        }
        self.0 /= 10;
        Some(result)
    }
}

fn func_sum_all_numbers(val: u64) -> u64 {
    return DigitEnumerator(val).into_iter().sum();
}

fn main() {
    let value = 123456;
    let result_sum = sum_all_numbers(value);
    let result_func_sum = func_sum_all_numbers(value);
    println!("{}", result_sum);
    println!("{}", result_func_sum);
    assert!(result_sum == result_func_sum);
}