mod_vs_use.md

Mod vs Use

TLDR

• Using use brings a Rust item into the current scope, use is primarily used to make code cleaner and less verbose
• Using mod defines a module which is a collection of Rust items, or literally brings the contents of a file and inserts in its place.
• There is no need to explicitly import crates in Rust using use. When you compile your crate, Cargo will handle this automatically.

Use

• use is like C++'s using-declaration, by using it we can make things less repetitive, and more concise
• Using use is mostly optional. It does not function like an import statement.

{} glob-like syntax

• use a::b::{c, d, e::f, g::h::i};

self keyword

• You can use the self keyword, allowing you to bring the common parent module into the namespace as well as any items you want to access
  • use std::collections::hash_map::{self, HashMap}

as keyword

• You can use as keyword to rename items and avoid naming conflicts
  • use a::b::{self as ab, c as abc}

asterisk wildcard syntax

• You can also use the asterisk wildcard syntax to bind all paths matching a given prefix
  • this is like C++'s using-directive

Mod

module source filenames

• We can write a mod statement without declaring a body. When you do this and compile your crate, Cargo will look a .rs file in the current directory with the name given after the mod declaration.

Imaging we have the following file structure with lib.rs containing pub mod utilities;

.
└── media
   ├── utilities.rs
   └── lib.rs

• Cargo brings the contents of utilities.rs and inserts it into the current file.
• This means that in lib.rs you can use any items you've written in utilities.rs as if they were actually written inside a mod utilities {} block
• By declaring utilities a module, you have added it to the tree hierarchy of your crate and the function download (inside utilities.rs) can now be accessed by its path media::utilities::download by anyone who installs your crate.
• We cannot replace pub mod utilities; line with a use statement. We have to declare utilities.rs as a module, so it's added to the crate structure

Reference

The difference between mod and use in Rust | panaetius.io