How do I extract a number in decimal representation from a `&[u8]` and compare it with an integer?

Here’s an example of my code:

use bytes::Bytes;
use regex::bytes::Regex as BytesRegex;

fn main() {
    let val = b"2020-01-01";
    let my_regex = BytesRegex::new(r"\d{4}-(\d{2})-\d{2}").unwrap();
    let month = my_regex.captures(val).unwrap().get(1).unwrap();
    let month_digit = std::str::from_utf8(month.as_bytes()).unwrap().parse::<u8>().unwrap();
    println!("month smaller than 12: {}", month_digit<=12);
}

https://gist.github.com/rust-play/92d4e4855015317451abad775adceec1

Like this, I was able to print out the captured group as an unsigned integer. But, I had to go via std::str::from_utf8.

Is there a way to get the same result without converting to str?

>Solution :

This can be done easily with Iterator::fold and basic arithmetic:

let month_digit = month.as_bytes().iter().fold (0, |acc, c| acc*10 + (c - '0' as u8))

Playground