Rs
Rust Foundations
Module 1Getting StartedLesson 3 of 1015 min

Comments, Style & Cargo Mindset

How Rust projects are organized locally, what the playground can/can’t do, and how to write readable quant code.

Comments

rust
// line comment

/// Doc comment — for public APIs (shows in rustdoc)
fn mid(bid: f64, ask: f64) -> f64 {
    (bid + ask) / 2.0 // trailing comment
}

Local vs playground

Playground (this site) Local cargo
Crates almost none crates.io
Binary single snippet project with modules
Tests limited cargo test
Release opts constrained --release for benches

Mental model for local projects:

my-pricer/
  Cargo.toml      # dependencies
  src/main.rs     # binary entry
  src/lib.rs      # library root (optional)
  src/bs.rs       # module

You don’t need Cargo to learn here — but knowing it exists means you won’t be surprised later when we talk about serde and rayon.

Style that scales

  • Prefer clarity over clever one-liners in pricing code
  • Name variables after domain terms: spot, strike, time_to_expiry, rate
  • Keep functions small; pure math functions are easy to test

Exercise

Rewrite noisy names into clear domain names and document a tiny helper.

Challenge

Add spread(bid, ask) with a doc comment and print mid + spread for two symbols.

Tips
  • /// doc comments go directly above the item
  • Domain names beat x/y/z in finance code
  • Playground is for learning; Cargo is for real systems

Try it live

Comments, Style & Cargo MindsetRust 2021
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Output
Press Run to compile and execute.