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playground.rs

use std::str::FromStr;

#[derive(Debug)]
enum Version { Version1, Version2 }

#[derive(Debug)]
enum ParseError { InvalidSyntax, UnsupportedVersion }

fn parse_version(line: String) -> Result<Version, ParseError> {
    let mut split = line.split("=");
    if split.clone().count() != 2 {
        // old config without version number, assume Version1
        return Ok(Version::Version1);
    }
    if split.next().unwrap() != "version" {
        return Err(ParseError::InvalidSyntax);
    }
    let version = match i32::from_str(split.next().unwrap()).unwrap() {
        1 => Version::Version1,
        2 => Version::Version2,
        _ => return Err(ParseError::UnsupportedVersion),
    };
        
    Ok(version)
}

fn main() {
    println!("{:?}", parse_version(String::from("something")));
    println!("{:?}", parse_version(String::from("version=1")));
    println!("{:?}", parse_version(String::from("version=2")));
    println!("{:?}", parse_version(String::from("version=3")));
    println!("{:?}", parse_version(String::from("something=3")));
}