How to Create Public APIs with Proper Encapsulation in Rust

Create public APIs in Rust by marking modules and items with pub while keeping internal helpers private, then re-export only the necessary symbols at the crate root.

// src/lib.rs
pub mod kinds;
pub mod utils;

pub use kinds::PrimaryColor;
pub use utils::mix;

// src/kinds.rs
pub enum PrimaryColor {
    Red,
    Yellow,
    Blue,
}

// src/kinds.rs (continued)
pub enum SecondaryColor {
    Orange,
    Green,
    Purple,
}

// src/utils.rs
use crate::kinds::*;

pub fn mix(c1: PrimaryColor, c2: PrimaryColor) -> SecondaryColor {
    SecondaryColor::Orange
}

This structure exposes PrimaryColor and mix to users while hiding internal details like SecondaryColor unless explicitly re-exported.

You control what parts of your code others can see by marking specific functions or types as public. Think of it like a restaurant menu: you show customers the dishes they can order, but keep the kitchen recipes and prep steps hidden. This keeps your code organized and prevents users from relying on internal details that might change.