rust-ops

Rust Operations

Comprehensive Rust skill covering ownership, async, error handling, and the production ecosystem.

Ecosystem facts verified as of 2026-07.

Staleness check: python scripts/check-rust-facts.py --offline asserts the catalogued version-bearing facts (tokio, axum, serde) are still named in the prose and the dated currency note above is present; run --live to confirm each crate's crates.io major still matches the documented major. Catalog: assets/rust-facts.json.

Ownership Quick Reference

Who owns the value?
│
├─ Need to transfer ownership
│  └─ Move: let s2 = s1;  (s1 is invalid after this)
│
├─ Need to read without owning
│  └─ Shared borrow: &T (multiple allowed, no mutation)
│
├─ Need to mutate without owning
│  └─ Exclusive borrow: &mut T (only one, no other borrows)
│
├─ Need to share ownership across threads
│  └─ Arc<T> (atomic reference counting)
│     └─ Need mutation too? Arc<Mutex<T>>
│
├─ Need to share ownership single-threaded
│  └─ Rc<T> (reference counting, not Send)
│     └─ Need mutation too? Rc<RefCell<T>>
│
└─ Need to avoid cloning large data
   └─ Cow<'a, T> (clone-on-write, borrows when possible)

The Borrow Rules

1. At any time, you can have either one &mut T or any number of &T
2. References must always be valid (no dangling)
3. These rules are enforced at compile time (zero runtime cost)

Error Handling Decision Tree

What kind of error?
│
├─ Operation might not have a value (no error info needed)
│  └─ Option<T>: Some(value) or None
│
├─ Library code (callers need to match on error variants)
│  └─ thiserror: #[derive(Error)] enum with variants
│     └─ Each variant can wrap source errors with #[from]
│
├─ Application code (just need context, not matching)
│  └─ anyhow: anyhow::Result<T>, .context("msg")
│
├─ Converting between error types
│  └─ impl From<SourceError> for MyError
│     └─ Or use #[from] with thiserror
│
└─ Truly unrecoverable (violating invariants)
   └─ panic!() or unwrap() - avoid in library code