Filesystem Hierarchy

Omitting the module content will tell Rust to look for it in another file:

  1. mod garden;

This tells Rust that the garden module content is found at src/garden.rs. Similarly, a garden::vegetables module can be found at src/garden/vegetables.rs.

The crate root is in:

  • src/lib.rs (for a library crate)
  • src/main.rs (for a binary crate)

Modules defined in files can be documented, too, using “inner doc comments”. These document the item that contains them — in this case, a module.

  1. //! This module implements the garden, including a highly performant germination
  2. //! implementation.
  4. // Re-export types from this module.
  5. pub use garden::Garden;
  6. pub use seeds::SeedPacket;
  8. /// Sow the given seed packets.
  9. pub fn sow(seeds: Vec<SeedPacket>) {
  10.     todo!()
  11. }
  13. /// Harvest the produce in the garden that is ready.
  14. pub fn harvest(garden: &mut Garden) {
  15.     todo!()
  16. }

This slide should take about 5 minutes.

  • Before Rust 2018, modules needed to be located at module/mod.rs instead of module.rs, and this is still a working alternative for editions after 2018.

  • The main reason to introduce filename.rs as alternative to filename/mod.rs was because many files named mod.rs can be hard to distinguish in IDEs.

  • Deeper nesting can use folders, even if the main module is a file:

    1. src/
    2. ├── main.rs
    3. ├── top_module.rs
    4. └── top_module/
    5.     └── sub_module.rs

  • The place rust will look for modules can be changed with a compiler directive:

    1. #[path = "some/path.rs"]
    2. mod some_module;

    This is useful, for example, if you would like to place tests for a module in a file named some_module_test.rs, similar to the convention in Go.