rust 55 lines · 8 steps

Parsing and ordering semantic versions in Rust

A SemVer struct that parses from a string and orders correctly, treating pre-release builds as older than their release.

Explained by highlit

Intermediate parsing trait-implementation ordering error-handling semver

1use std::cmp::Ordering;
2use std::str::FromStr;
3 
4#[derive(Debug, Clone, PartialEq, Eq)]
5pub struct SemVer {
6    pub major: u64,
7    pub minor: u64,
8    pub patch: u64,
9    pub pre_release: Option<String>,
10}
11 
12#[derive(Debug, thiserror::Error)]
13pub enum ParseError {
14    #[error("missing {0} component")]
15    MissingComponent(&'static str),
16    #[error("invalid number in version: {0}")]
17    InvalidNumber(#[from] std::num::ParseIntError),
18}
19 
20impl FromStr for SemVer {
21    type Err = ParseError;
22 
23    fn from_str(s: &str) -> Result<Self, Self::Err> {
24        let (core, pre_release) = match s.trim_start_matches('v').split_once('-') {
25            Some((core, pre)) => (core, Some(pre.to_string())),
26            None => (s.trim_start_matches('v'), None),
27        };
28 
29        let mut parts = core.split('.');
30        let major = parts.next().ok_or(ParseError::MissingComponent("major"))?.parse()?;
31        let minor = parts.next().ok_or(ParseError::MissingComponent("minor"))?.parse()?;
32        let patch = parts.next().ok_or(ParseError::MissingComponent("patch"))?.parse()?;
33 
34        Ok(SemVer { major, minor, patch, pre_release })
35    }
36}
37 
38impl Ord for SemVer {
39    fn cmp(&self, other: &Self) -> Ordering {
40        (self.major, self.minor, self.patch)
41            .cmp(&(other.major, other.minor, other.patch))
42            .then_with(|| match (&self.pre_release, &other.pre_release) {
43                (None, None) => Ordering::Equal,
44                (None, Some(_)) => Ordering::Greater,
45                (Some(_), None) => Ordering::Less,
46                (Some(a), Some(b)) => a.cmp(b),
47            })
48    }
49}
50 
51impl PartialOrd for SemVer {
52    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
53        Some(self.cmp(other))
54    }
55}

01 / 01

STEP 01

Walkthrough

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Three takeaways

1Implementing FromStr gives your type free parse() and str::parse integration.
2Comparing tuples lexicographically is a concise way to order by multiple fields in priority order.
3SemVer's rule that any pre-release sorts below its release must be encoded explicitly, since None must beat Some.

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