Parsing a range of values in rust, suitable for command line clap parsing

parse_range.rs

// https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=7d2fd8dc461ab1fc7216eb4e68c4517d

use std::str::FromStr;

#[derive(Clone, Debug, Eq, PartialEq)]
pub(crate) enum ResOpt {
    Fixed(u8),
    Range(u8, u8),
}

impl FromStr for ResOpt {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<ResOpt, anyhow::Error> {
        match s.split("..").collect::<Vec<&str>>().as_slice() {
            // "res"
            [res] => {
                let res = u8::from_str(res)?;
                Ok(ResOpt::Fixed(res))
            }

            // "Min.."
            [min, ""] => {
                let min = u8::from_str(min)?;
                Ok(ResOpt::Range(min, 15))
            }

            // "..Max"
            ["", max] => {
                let max = u8::from_str(max)?;
                Ok(ResOpt::Range(0, max))
            }

            // "Min..Max"
            [min, max] => {
                let min = u8::from_str(min)?;
                let max = u8::from_str(max)?;
                Ok(ResOpt::Range(min, max))
            }
            _ => anyhow::bail!("{} is not a valid range", s),
        }
    }
}

fn main() {
    assert_eq!(ResOpt::from_str("12").unwrap(), ResOpt::Fixed(12));
    assert_eq!(ResOpt::from_str("9..").unwrap(), ResOpt::Range(9, 15));
    assert_eq!(ResOpt::from_str("..12").unwrap(), ResOpt::Range(0, 12));
    assert_eq!(ResOpt::from_str("9..12").unwrap(), ResOpt::Range(9, 12));
    assert!(ResOpt::from_str("9.12").is_err(),);
}