Summary - Crates and packages

Combine a binary + library crate and a workspace to build a monorepo.

Crates and packages summary

A crate is a compilation unit: a binary (main.rs) or a library (lib.rs). A package is defined by Cargo.toml and lists dependencies; Cargo.lock locks the exact versions. Versions follow semver and "1.2" means ^1.2 by default. Features turn on optional parts (#[cfg(feature = "..")]). A workspace manages several packages with one lock file and target folder.

Parsing versions

Converting a version string to numbers and comparing as vectors gives the right order; a Vec also compares lexicographically:

fn ayristir(s: &str) -> Vec<u32> {
    s.split('.').map(|p| p.parse().unwrap()).collect()
}

let a = ayristir("1.4.2");    // [1, 4, 2]
let b = ayristir("1.10.0");   // [1, 10, 0]
println!("{}", a < b);        // true

Real projects use the semver crate for this; it also handles pre-release tags (1.0.0-beta) correctly.

Exercise Compare versions

Write the ayristir function above. For "1.4.2" and "1.10.0", print the results of the numeric comparison (a < b) and the plain string comparison, separated by a space.

Show example solution

fn ayristir(s: &str) -> Vec<u32> {
    s.split('.').map(|p| p.parse().unwrap()).collect()
}

fn main() {
    let (x, y) = ("1.4.2", "1.10.0");
    println!("{} {}", ayristir(x) < ayristir(y), x < y);
}

Test yourself

Why does the string comparison <code>"1.4.2" < "1.10.0"</code> give a wrong result?
- It gives the right result
- It doesn't compile
- It panics
- Strings compare character by character; since "4" > "1", it's false
Show answer

Strings compare character by character; since "4" > "1", it's false — Versions must be converted to numbers and compared component by component.

Split at dots

s.____('.').map(|p| p.parse().unwrap()).collect()

Show answer

s.split('.').map(|p| p.parse().unwrap()).collect()

Group summary

lib.rs

Library crate
Cargo.lock

Exact versions
^1.2

<2.0.0
[workspace]

Multiple packages

Next lesson: Unit test

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