Semantic version parsing and comparison.
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Semantic version parsing and comparison.

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Semantic versioning (see is a set of rules for assigning version numbers.

SemVer and the Rust ecosystem

Rust itself follows the SemVer specification, as does its standard libraries. The two are not tied together.

Cargo, Rust's package manager, uses SemVer to determine which versions of packages you need installed.


To use semver, add this to your [dependencies] section:

semver = "0.9.0"

And this to your crate root:

extern crate semver;


At its simplest, the semver crate allows you to construct Version objects using the parse method:

use semver::Version;

assert!(Version::parse("1.2.3") == Ok(Version {
   major: 1,
   minor: 2,
   patch: 3,
   pre: vec!(),
   build: vec!(),

If you have multiple Versions, you can use the usual comparison operators to compare them:

use semver::Version;

assert!(Version::parse("1.2.3-alpha")  != Version::parse("1.2.3-beta"));
assert!(Version::parse("1.2.3-alpha2") >  Version::parse("1.2.0"));


The semver crate also provides the ability to compare requirements, which are more complex comparisons.

For example, creating a requirement that only matches versions greater than or equal to 1.0.0:

use semver::Version;
use semver::VersionReq;

let r = VersionReq::parse(">= 1.0.0").unwrap();
let v = Version::parse("1.0.0").unwrap();

assert!(r.to_string() == ">= 1.0.0".to_string());

It also allows parsing of ~x.y.z and ^x.y.z requirements as defined at

Tilde requirements specify a minimal version with some updates:

~1.2.3 := >=1.2.3 <1.3.0
~1.2   := >=1.2.0 <1.3.0
~1     := >=1.0.0 <2.0.0

Caret requirements allow SemVer compatible updates to a specified version, 0.x and 0.x+1 are not considered compatible, but 1.x and 1.x+1 are.

0.0.x is not considered compatible with any other version. Missing minor and patch versions are desugared to 0 but allow flexibility for that value.

^1.2.3 := >=1.2.3 <2.0.0
^0.2.3 := >=0.2.3 <0.3.0
^0.0.3 := >=0.0.3 <0.0.4
^0.0   := >=0.0.0 <0.1.0
^0     := >=0.0.0 <1.0.0