rust_module_fuckery.md

Rust Module Fuckery

Why are Rust modules so hard to understand? There are two options, either Main.rs or Lib.rs. And crates are not packages etc.

The worst is, that if the main function in main.rs is missing (e.g. ure using rocket) and you try to run the main, it will not find the module main and avoid execution of that part of the program. Nice, right?

How to use Rust Modules using lib.rs

If you want to use a top level module from a lower module directory like src/bin you will be using lib.rs and multiple binary crates. After doing so you can asically delete the main.rs, if it does not contain a fn main

In lib.rs, assuming you have two modules, a sub module in src/bin/submodule.rs and a a top level module src/database.rs:

  // lib.rs
  pub mod database;

In the src/bin/submodule.rs you can improt the module specified in lib.rs:

// src/bin/submodule.rs
  use projectname::database;

How to run the new binary crates?

The (dis)advantage of multiple bin crates is obvious, you will need to execute them individually using --bin flag of the compiler / runner, e.g. cargo run --bin <fname without rs>

How to import stuff globally using lib.rs?

Nice to know is also that you can "import" external crates like Rocket or Diesel globally using Lib.rs:

// lib.rs
// your consts here
// your pub mods here

// Rust 2018+ convention (no macro_use needed)
extern crate rocket;
extern crate rocket_dyn_templates; // optional
extern crate diesel;

Note: Obviously the use keyword in the mentioned binary crates, so the module(s) (files), needs to be used to import the external crates.

How to find the project name?

In Cargo.toml is the project name defined!

[package]
name = "project_name"
...