Dividing Code Into Modules

We can write huge programs in one file, but dividing our code into smaller sections—known as modules in Rust—offers significant advantages:

• It’s much easier to find our map functionality in a file named map.rs than it is to remember that it’s somewhere around line 500 of an ever-growing main.rs.
• Cargo can compile modules concurrently, producing much better compilation times.
• Bugs are easier to find in self-contained code that limits linkages to other sections of code.

Modules may either be a single .rs file or a directory.

Crates and modules

Rust programs are divided into crates and modules. Crates are large groups of code with their own Cargo.toml file.

Our game is a crate. So is bracket-lib; every dependency we specify in Cargo is a ...