Modules and several files

Split a program into files with mod, make items visible with pub, and what is available without crates.

Runs in Zerethon IDE · Rust 1.87 Official Rust documentation ↗

main.rs

mod geometry;

fn main() {
    println!("{}", geometry::area(3, 4));
    println!("{}", geometry::shapes::NAME);
}

geometry.rs

pub mod shapes {
    pub const NAME: &str = "shapes ok";
}

pub fn area(width: i32, height: i32) -> i32 {
    width * height
}

Output

12
shapes ok

Two files: main.rs (the entry) and geometry.rs next to it.

The entry file is the crate root. mod geometry; loads geometry.rs (or geometry/mod.rs) from the same folder; a file that no mod names is not compiled.
Items are private to their module unless marked pub.
use std::collections::HashMap; brings a name into scope; the whole standard library is available.
There is no Cargo and no network, so crates from crates.io (rand, regex, serde…) cannot be used.

Official references