What Is the Difference Between mod.rs and Named Files in Rust 2018+?

In Rust 2018+, mod.rs is no longer required for inline modules or when using the mod name; syntax with a same-named file, whereas named files (e.g., mod.rs replaced by name.rs) are the standard way to define modules in modern editions. The compiler now automatically looks for name.rs or name/mod.rs when you declare mod name;, making the explicit mod.rs file optional unless you are using the directory-based module structure.

// src/lib.rs
mod utils; // Compiler looks for src/utils.rs OR src/utils/mod.rs

// src/utils.rs (Named file approach - preferred in 2018+)
pub fn helper() {
    println!("Helper function");
}

In Rust 2018 and later, you don't need a file named mod.rs inside a folder to define a module anymore. You can just create a file with the same name as your module (like utils.rs) and the compiler will find it automatically. This makes organizing code simpler because you don't have to create an extra file just to make the folder work as a module.