DEV Community

Subesh Yadav
Subesh Yadav

Posted on

🦀 Day 9 of #100DaysOfRust — Managing Growing Projects in Rust 🧱

#rust #webdev #learning #100daysofrust

As Rust projects grow in complexity, organizing code becomes essential. Today, I dived deep into Rust's powerful module system—how packages, crates, and modules help structure code for better readability, maintainability, and reuse.

📦 Packages & Crates

✅ Crate:

A crate is the smallest unit of compilation in Rust. It can be:

  • A binary crate: builds to an executable (main.rs)
  • A library crate: provides reusable logic (lib.rs) 
# Create a new binary crate
cargo new my_project
Enter fullscreen mode Exit fullscreen mode

✅ Package:

A package is a bundle of one or more crates.

  • Contains a Cargo.toml file.
  • Can have multiple binary crates, one library crate.

🧠 Key Point: By convention:

  • src/main.rs → binary crate
  • src/lib.rs → library crate

Want multiple binaries? Add them in src/bin/.

📂 Modules and File Structure

Modules help you logically group related code and control visibility.

mod garden; // This tells Rust to look for src/garden.rs or src/garden/mod.rs
Enter fullscreen mode Exit fullscreen mode

In garden.rs, you can further define submodules:

pub mod vegetables;
Enter fullscreen mode Exit fullscreen mode

And in vegetables.rs:

#[derive(Debug)]
pub struct Asparagus {}
Enter fullscreen mode Exit fullscreen mode

🔁 Module Tree Example:

crate
└── garden
    └── vegetables
        └── Asparagus
Enter fullscreen mode Exit fullscreen mode

🔐 Privacy: Public vs Private

By default, items inside a module are private. Use pub to make them public.

pub mod garden {
    pub mod vegetables {
        #[derive(Debug)]
        pub struct Asparagus {}
    }
}
Enter fullscreen mode Exit fullscreen mode

To access:

use crate::garden::vegetables::Asparagus;

fn main() {
    let veggie = Asparagus {};
    println!("{:?}", veggie);
}
Enter fullscreen mode Exit fullscreen mode

🧭 Paths in Modules

Absolute Path:

crate::garden::vegetables::Asparagus
Enter fullscreen mode Exit fullscreen mode

Relative Path:

super::vegetables::Asparagus
Enter fullscreen mode Exit fullscreen mode

Use use to simplify:

use crate::garden::vegetables::Asparagus;
Enter fullscreen mode Exit fullscreen mode

Then:

let veg = Asparagus {};
Enter fullscreen mode Exit fullscreen mode

🧪 Module Cheat Sheet

  • Start with mod your_module; in the crate root.
  • Place module files in:
  • src/your_module.rs
  • src/your_module/mod.rs
  • Declare submodules in sub-files.
  • Use pub for visibility.
  • Simplify paths with use.

📁 Real Example File Structure

backyard/
├── Cargo.toml
└── src/
    ├── main.rs          # crate root (binary)
    ├── garden.rs        # contains `pub mod vegetables`
    └── garden/
        └── vegetables.rs
Enter fullscreen mode Exit fullscreen mode

And your code:

main.rs

use crate::garden::vegetables::Asparagus;

pub mod garden;

fn main() {
    let plant = Asparagus {};
    println!("I'm growing {:?}", plant);
}
Enter fullscreen mode Exit fullscreen mode

garden.rs

pub mod vegetables;
Enter fullscreen mode Exit fullscreen mode

vegetables.rs

#[derive(Debug)]
pub struct Asparagus;
Enter fullscreen mode Exit fullscreen mode

🧠 Summary

Today’s learning focused on organizing Rust projects for scale and clarity.

  • 📦 Packages group crates.
  • 🧱 Crates are the compilation units.
  • 🧭 Modules help logically separate features.
  • 🔐 Visibility is opt-in (pub).
  • 🧵 Paths and use streamline access to items.

Rust enforces structure and clarity by design. Mastering this early on helps you grow clean, robust codebases.

📌 Tomorrow, I’ll dive deeper into visibility, pub use, and real-world structuring in Rust!

Let me know your thoughts or questions in the comments! 👇

Top comments (0)