Modules & Organization

Rust’s modules are similar to JS/TS files and folders, but with much more explicit control over visibility.

ABSTRACT: 🧩 Analogy for Frontend Developers

• mod is like a file or folder: It defines a boundary of code.
• pub is like export: It makes an item available to the outside world.
• use is like import: It brings an item into your current scope.

🏗️ mod and pub (The JS export)

In JS, everything in a file is “internal” until you export it. In Rust, everything is private by default.

mod my_module {
    pub fn public_fn() {} // ⬅️ This is your JS `export`
    fn private_fn() {}    // ⬅️ This is an internal function
}

NOTE: Module Structure

• Inline: mod name { ... } (Great for tests or small components).
• Separate Files: Create a file named my_module.rs and then in main.rs, use mod my_module;.

🎨 The Module Tree

Rust organizes code like a filesystem.

// src/lib.rs (Crate Root)
mod front_of_house {
    pub mod hosting {
        pub fn add_to_waitlist() {}
    }
}

pub fn eat_at_restaurant() {
    // Absolute Path (starts with `crate::`)
    crate::front_of_house::hosting::add_to_waitlist();

    // Relative Path (starts with module name)
    front_of_house::hosting::add_to_waitlist();
}

WARNING: ⚠️ Privacy Rules

A parent cannot see into a child’s private items, but a child can see into its parent’s items using super.

mod back_of_house {
    fn fix_incorrect_order() {
        super::deliver_order(); // ⬅️ Accessing parent (like `../../` in JS)
    }
}

📥 use (The JS import)

Bring items into scope to avoid long paths.

use std::collections::HashMap;
use std::io::Result as IoResult; // Aliasing (like `import { x as y }`)

fn main() {
    let mut map = HashMap::new();
}

💡 Takeaway for Frontend

Rust’s mod is like your folder structure, and pub is like export. The biggest change: in JS, everything in a file is “visible” to the file. In Rust, you have to explicitly pub modules AND the items inside them to make them accessible from the outside. Use use to pull that code in just like an import.