Module System

Libraries and Binaries

• src/main.rs - Binary will be created using this

• src/lib.rs - Root library module

• All items in library are private by default. So we need to use pub keyword

• To use a method from library, we need to provide a absolute path.

// src/lib.rs

pub fn greet() {
    println!("Hello world");
}

// src/main.rs

fn main() {
    hello::greet();
}

The word hello before the function greet is the project name specified in Cargo.toml file

The use keyword

Helpful to avoid specifying the absolute path everytime a library function is used. Sometimes this is also referred to as importing

use hello::greet;

fn main() {
    greet();
}

Dependencies

• A dependency needs to be added to the Cargo.toml file before used
• A function from a dependency can be used both in library src/lib.rs or binary src/main.rs

[package]
name = "hello"
version = "0.1.0"
edition = "2021"

[dependencies]
rand = "0.8.5"

We can use absolute path rand::thread_rng().gen_range

use rand::Rng;

fn main() {
    let x = rand::thread_rng().gen_range(5..9);
    println!("{}", x);
}

or bringing that function to the scope

use rand::Rng;
use rand::thread_rng;

fn main() {
    let x = thread_rng().gen_range(1..100);
    println!("{}", x);
}