Separating Modules into Different Files

As modules grow, separate them into individual files for better organization. Unlike JavaScript/TypeScript where files are implicit modules, Rust requires explicit module declarations.

Moving Modules to Files

Starting from inline modules, extract them to separate files:

mod front_of_house;

pub use crate::front_of_house::hosting;

pub fn eat_at_restaurant() {
    hosting::add_to_waitlist();
}
 
pub mod hosting {
    pub fn add_to_waitlist() {}
}

The mod declaration loads the file once—it’s not an “include” operation. Other files reference the loaded module via its declared path.

Extracting Submodules

For submodules, create a directory structure:

pub mod hosting;
 
pub fn add_to_waitlist() {}

The file location must match the module hierarchy—hosting goes in src/front_of_house/hosting.rs because it’s a child of front_of_house.

File Path Conventions

Rust supports two file organization styles:

Modern style (recommended):

  • src/front_of_house.rs
  • src/front_of_house/hosting.rs

Legacy style (still supported):

  • src/front_of_house/mod.rs
  • src/front_of_house/hosting/mod.rs

Don’t mix styles within the same project to avoid confusion.

Summary

Rust’s module system provides explicit control over code organization and visibility:

  • Packages contain crates with Cargo.toml manifests
  • Crates are compilation units (binary or library)
  • Modules organize code with privacy controls (private by default)
  • Paths address items using :: syntax (absolute with crate:: or relative)
  • use creates local shortcuts to reduce path repetition
  • pub exposes items across module boundaries

This system enforces encapsulation at compile time, unlike JavaScript’s runtime-based privacy patterns.