How to Create an Internal (Private) Module in Rust

To create an internal (private) module in Rust, define the module without the pub keyword and keep its items private by omitting pub from them.

mod internal_utils {
    fn helper() {
        // This function is only accessible within this module
    }

    pub fn public_helper() {
        // This is accessible outside the module
    }
}

// internal_utils::helper() would fail here
internal_utils::public_helper(); // This works

By default, modules and their contents are private to the parent module unless explicitly marked pub.

An internal module is like a private room in your code where you can store helper functions that only other parts of your own project can see. You create one by simply writing mod name without adding the pub word. This keeps your internal logic hidden from anyone using your library, similar to keeping your kitchen tools inside the kitchen rather than on the dining table.