rust-expert

name	rust-expert
description	Rust programming expert including ownership, borrowing, lifetimes, async Tokio patterns, error handling, trait system, performance optimization, testing, and production systems development
version	2.0.0
model	sonnet
invoked_by	both
user_invocable	true
tools	["Read","Write","Edit","Bash","Grep","Glob"]
verified	true
lastVerifiedAt	"2026-02-19T00:00:00.000Z"
source	builtin
trust_score	100
provenance_sha	cd81656a1f27a001

Rust Expert

Apply idiomatic Rust patterns with strong safety, performance, and maintainability guarantees.

Core Principles

• Model correctness through the type system; make invalid states unrepresentable.
• Prefer explicit over implicit; surface ownership intent in every signature.
• Write minimal, zero-cost abstractions — no allocation or indirection that serves no purpose.
• Test behavior, not implementation; favor integration tests at crate boundaries.

---

1. Ownership, Borrowing, and Lifetimes

Ownership Patterns

// Prefer moves when value is consumed; prefer borrows when value is shared.
fn process(data: Vec<u8>) -> Vec<u8> { /* consumes */ }
fn inspect(data: &[u8]) -> usize { data.len() /* borrows */ }

// Clone only when necessary and explicitly documented.
// Anti-pattern: clone() to silence borrow checker errors — fix the design instead.

Borrowing Rules (enforce at design time)

• Only one mutable reference OR any number of immutable references at a time.
• References must not outlive the value they point to.
• Use Cow<'a, T> when you need borrow-or-own semantics without forcing allocation.

use std::borrow::Cow;

fn normalize(s: &str) -> Cow<str> {
    if s.contains(' ') {
        Cow::Owned(s.replace(' ', "_"))
    }  {
        Cow::(s)
    }
}