Modules Basics

7 examples - 5 basic, 2 intermediate - for Rust module system.

Prerequisites

• Cargo Basics

Basic Examples

1. Inline Module

mod math {
    pub fn add(a: i32, b: i32) -> i32 { a + b }
}
fn main() { println!("{}", math::add(1, 2)); }

2. File Module

// lib.rs: mod config;
// config.rs: pub fn port() -> u16 { 8080 }

mod config; loads config.rs or config/mod.rs.

3. pub Visibility

mod api {
    pub fn ping() {}
    fn secret() {}
}

Only ping visible outside api.

4. Nested Modules

mod outer {
    pub mod inner { pub fn f() {} }
}

Path: outer::inner::f.

5. use Import

use std::collections::HashMap;

Related: use & Paths

Intermediate Examples

6. mod.rs Directory

src/
  lib.rs
  models/
    mod.rs
    user.rs

mod user; in models/mod.rs.

7. Crate Root

Binary: main.rs. Library: lib.rs - crate root module.

Related: Modules & Crates Best Practices

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+.