Rust - Crates - Module

Modules are used to organize code within a crate into groups and control the privacy of items (public vs private). The C++ counterpart would be a namespace, except Rust takes it a step further.

Modules are created by using the mod keyword.

The modules in src/main.rs and src/lib.rs are called "crate roots" and is nested under crate.

Modules are private by default (like C++ private methods in a class). To make them public, you have to add the pub keyword. All parents of that module are now public, but children are still private unless specified otherwise.pub can be used on structs, enums, functions, and methods as well.

The keyword super allows you to refer to something in the parent's scope.

Example:

mod garden {
    // Nest a module inside of another
    pub mod food {
        // Add structs, enums, constants, traits, modules, functions, etc. here
        pub fn harvest() {
            super::soil::amount();
            super::super::plant_garden();
        }
        fn water() {}
    }

    pub mod soil {
        pub fn quality() {}
    
        pub fn amount() { quality(); }
    }
}

pub fn plant_garden() {
    // Relative path
    garden::soil::quality();
    // Absolute path
    crate::garden::soil::amount();
}

fn main() {
    // To access harvest, you'll have to do:
    crate::garden::food::harvest();
    // Both food and harvest must be marked as pub
}