Crates & Packages

A package (Cargo project) contains one or more crates (compilation units): library (lib.rs) and/or binaries (main.rs, bin/*.rs).

Recipe

[package]
name = "myapp"
version = "0.1.0"
edition = "2024"
 
[lib]
name = "myapp"
path = "src/lib.rs"
 
[[bin]]
name = "cli"
path = "src/bin/cli.rs"

When to reach for this: Splitting reusable library from CLI binary in one repo.

Working Example

// src/lib.rs
pub fn core_logic() -> i32 { 42 }
 
// src/main.rs
fn main() {
    println!("{}", myapp::core_logic());
}

What this demonstrates:

• Library crate exposes core_logic
• Binary depends on library crate in same package
• Package name matches lib for use myapp

Deep Dive

cdylib/staticlib for FFI. autobins false to control bins. build.rs for build scripts.

Gotchas

• Binary-only crate no lib - Hard to integration test logic. Fix: Extract lib.
• Name mismatch lib vs package - Import confusion. Fix: Align names or document.
• Multiple bins share code - Duplication in mains. Fix: Shared lib module.
• pub in binary only - Not reusable. Fix: lib.rs.
• Edition mismatch deps - Resolver picks compatible.

Alternatives

FAQs

Related

• Cargo Basics
• Cargo.toml Explained
• Workspaces
• Project Structure Patterns

Stack versions: This page was written for Rust 1.97.0 (edition 2024), Tokio 1.x, Axum 0.8, serde 1.0, sqlx 0.8, clap 4, and Polars 0.46+.