17.5 Best Practices and Advanced Topics

As Rust codebases grow, so do the challenges of organizing many modules, crates, and packages. Here are some guidelines and advanced techniques to keep your architecture coherent and modular.

17.5.1 Guidelines for Large Projects

  • Meaningful Names: Use concise, descriptive module names. Overly generic or overly long names complicate navigation.
  • Reasonable Depth: Deeply nested modules lead to unwieldy paths. Flatten where possible for clarity.
  • Re-exports for Simplicity: If you have a useful item nested multiple levels deep, consider re-exporting it at a more accessible level to provide a clean public API.
  • Consistent Layout: Keep your directory structure predictable. Mixing mod.rs with the modern style (math.rs + math/) can confuse your collaborators and future self.
  • Document Public Items: Use /// for documentation comments on modules, structs, enums, and functions that form part of your crate’s public API.

17.5.2 Conditional Compilation

Rust’s conditional compilation attributes (#[cfg(...)]) let you toggle code depending on OS, architecture, or cargo feature flags:

#[cfg(target_os = "linux")]
fn linux_specific() {
    println!("Linux-only code");
}

This feature is crucial for cross-platform code and for selectively enabling optional functionality.

17.5.3 Avoiding Cyclic Imports

Rust prohibits circular dependencies between modules. If two modules need to share types or functions, move those shared items into a third “common” module or library, then import that module from both sides. This approach ensures a clear, acyclic dependency graph.

17.5.4 When to Split Code Into Separate Crates

  • Shared Library Logic: If multiple binaries need the same logic, placing that code in a dedicated library crate can be more convenient and maintainable than copying files.
  • Independent Release Cycle: If part of your code could be versioned and published on its own (e.g., a utility crate), it might warrant a separate crate.
  • Clear Boundaries: Splitting code across crates can reinforce architectural constraints, making sure certain layers or functionalities depend in only one direction.