Rust Modules

Written 2021-03-22

Source: https://doc.rust-lang.org/rust-by-example/mod.html
Each file and directory is a module by default.
In a directory, mod.rs is the "main" file for the module and the other files are nested modules under that module. Other files must be referenced with mod FILENAME to be included.
You can also define nested modules within the same file.
Visibility
- Items in modules are private by default
- pub makes them visible outside the module.
- Nested modules within a file can be declared with pub mod to make them public.
- pub(in path) lets you define specific paths where the item should be importable.
  - e.g. pub(in crate::other_module)
- pub(self) is public only within the current module, which is effectively the same as the default private visibility.
- pub(super) makes it visible to the parent module.
- pub(crate) makes it visible within the whole crate.
- Notably, access to any item msut be allowed to the importer along the whole chain. Declaring a function pub in a module that isn't visible outside the crate doesn't actually expose that field to external importers. The module itself must be exposed in some way too.
- In structures, fields and functions are also private by default even if the structure itself is public. All the pub modifiers above apply when you do want to expose them.
use syntax
- You can access anything visible with the entire full path to the item, but use makes it simpler.
- use crate::a::b::{ fn1, fn2 } will expose fn1 and fn2 in the module's scope.
- use X as Y will rename the function too.
- pub use reexports an imported module or other item.
super::other_module::X and self::X can help for relative references and to remove ambiguity.