Rust Patterns

affaan-m/ECC/.kiro/skills/rust-patterns

by affaan-mef648e01899ba3e8dc6371642deaaf64b4477775No license275K starsListed Oct 9, 2026Updated Oct 9, 2026Repository updated 4 days ago

Idiomatic Rust patterns, ownership, error handling, traits, concurrency, and best practices for building safe, performant applications.

Instructions onlySoftware Development
AI-generated overview

Guides writing, reviewing, and refactoring idiomatic Rust code across ownership, errors, traits, concurrency, and crate structure.

What it does
This skill provides reference guidance and code examples for idiomatic Rust development. It covers ownership and borrowing, error handling with Result, thiserror and anyhow, enums and exhaustive matching, traits and generics, iterators, concurrency with Arc >, channels and async, unsafe code rules, and module and crate organization. It also lists cargo tooling commands, a quick-reference idiom table, and anti-patterns to avoid.
When to use it
Use it when writing new Rust code, reviewing or refactoring existing Rust code, or designing crate structure and module layout. It suits work where idiomatic conventions and type-safety practices should be applied or checked.
Requirements
No scripts or assets are included; it is instructions only. The examples reference Rust crates such as thiserror, anyhow, tokio, and reqwest, and cargo commands, but nothing is executed by the skill itself.

Rust Development Patterns

Idiomatic Rust patterns and best practices for building safe, performant, and maintainable applications.

When to Use

  • Writing new Rust code
  • Reviewing Rust code
  • Refactoring existing Rust code
  • Designing crate structure and module layout

How It Works

This skill enforces idiomatic Rust conventions across six key areas: ownership and borrowing to prevent data races at compile time, Result/? error propagation with thiserror for libraries and anyhow for applications, enums and exhaustive pattern matching to make illegal states unrepresentable, traits and generics for zero-cost abstraction, safe concurrency via Arc<Mutex<T>>, channels, and async/await, and minimal pub surfaces organized by domain.

Core Principles

1. Ownership and Borrowing

Rust's ownership system prevents data races and memory bugs at compile time.

rust
// Good: Pass references when you don't need ownershipfn process(data: &[u8]) -> usize {    data.len()}
// Good: Take ownership only when you need to store or consumefn store(data: Vec<u8>) -> Record {    Record { payload: data }}
// Bad: Cloning unnecessarily to avoid borrow checkerfn process_bad(data: &Vec<u8>) -> usize {    let cloned = data.clone(); // Wasteful — just borrow    cloned.len()}

Use Cow for Flexible Ownership

rust
use std::borrow::Cow;
fn normalize(input: &str) -> Cow<'_, str> {    if input.contains(' ') {        Cow::Owned(input.replace(' ', "_"))    } else {        Cow::Borrowed(input) // Zero-cost when no mutation needed    }}

Error Handling

Use Result and ? — Never unwrap() in Production

rust
// Good: Propagate errors with contextuse anyhow::{Context, Result};
fn load_config(path: &str) -> Result<Config> {    let content = std::fs::read_to_string(path)        .with_context(|| format!("failed to read config from {path}"))?;    let config: Config = toml::from_str(&content)        .with_context(|| format!("failed to parse config from {path}"))?;    Ok(config)}
// Bad: Panics on errorfn load_config_bad(path: &str) -> Config {    let content = std::fs::read_to_string(path).unwrap(); // Panics!    toml::from_str(&content).unwrap()}

Library Errors with thiserror, Application Errors with anyhow

rust
// Library code: structured, typed errorsuse thiserror::Error;
#[derive(Debug, Error)]pub enum StorageError {    #[error("record not found: {id}")]    NotFound { id: String },    #[error("connection failed")]    Connection(#[from] std::io::Error),    #[error("invalid data: {0}")]    InvalidData(String),}
// Application code: flexible error handlinguse anyhow::{bail, Result};
fn run() -> Result<()> {    let config = load_config("app.toml")?;    if config.workers == 0 {        bail!("worker count must be > 0");    }    Ok(())}

Option Combinators Over Nested Matching

rust
// Good: Combinator chainfn find_user_email(users: &[User], id: u64) -> Option<String> {    users.iter()        .find(|u| u.id == id)        .map(|u| u.email.clone())}
// Bad: Deeply nested matchingfn find_user_email_bad(users: &[User], id: u64) -> Option<String> {    match users.iter().find(|u| u.id == id) {        Some(user) => match &user.email {            email => Some(email.clone()),        },        None => None,    }}

Enums and Pattern Matching

Model States as Enums

rust
// Good: Impossible states are unrepresentableenum ConnectionState {    Disconnected,    Connecting { attempt: u32 },    Connected { session_id: String },    Failed { reason: String, retries: u32 },}
fn handle(state: &ConnectionState) {    match state {        ConnectionState::Disconnected => connect(),        ConnectionState::Connecting { attempt } if *attempt > 3 => abort(),        ConnectionState::Connecting { .. } => wait(),        ConnectionState::Connected { session_id } => use_session(session_id),        ConnectionState::Failed { retries, .. } if *retries < 5 => retry(),        ConnectionState::Failed { reason, .. } => log_failure(reason),    }}

Exhaustive Matching — No Catch-All for Business Logic

rust
// Good: Handle every variant explicitlymatch command {    Command::Start => start_service(),    Command::Stop => stop_service(),    Command::Restart => restart_service(),    // Adding a new variant forces handling here}
// Bad: Wildcard hides new variantsmatch command {    Command::Start => start_service(),    _ => {} // Silently ignores Stop, Restart, and future variants}

Traits and Generics

Accept Generics, Return Concrete Types

rust
// Good: Generic input, concrete outputfn read_all(reader: &mut impl Read) -> std::io::Result<Vec<u8>> {    let mut buf = Vec::new();    reader.read_to_end(&mut buf)?;    Ok(buf)}
// Good: Trait bounds for multiple constraintsfn process<T: Display + Send + 'static>(item: T) -> String {    format!("processed: {item}")}

Trait Objects for Dynamic Dispatch

rust
// Use when you need heterogeneous collections or plugin systemstrait Handler: Send + Sync {    fn handle(&self, request: &Request) -> Response;}
struct Router {    handlers: Vec<Box<dyn Handler>>,}
// Use generics when you need performance (monomorphization)fn fast_process<H: Handler>(handler: &H, request: &Request) -> Response {    handler.handle(request)}

Newtype Pattern for Type Safety

rust
// Good: Distinct types prevent mixing up argumentsstruct UserId(u64);struct OrderId(u64);
fn get_order(user: UserId, order: OrderId) -> Result<Order> {    // Can't accidentally swap user and order IDs    todo!()}
// Bad: Easy to swap argumentsfn get_order_bad(user_id: u64, order_id: u64) -> Result<Order> {    todo!()}

Structs and Data Modeling

Builder Pattern for Complex Construction

rust
struct ServerConfig {    host: String,    port: u16,    max_connections: usize,}
impl ServerConfig {    fn builder(host: impl Into<String>, port: u16) -> ServerConfigBuilder {        ServerConfigBuilder { host: host.into(), port, max_connections: 100 }    }}
struct ServerConfigBuilder { host: String, port: u16, max_connections: usize }
impl ServerConfigBuilder {    fn max_connections(mut self, n: usize) -> Self { self.max_connections = n; self }    fn build(self) -> ServerConfig {        ServerConfig { host: self.host, port: self.port, max_connections: self.max_connections }    }}
// Usage: ServerConfig::builder("localhost", 8080).max_connections(200).build()

Iterators and Closures

Prefer Iterator Chains Over Manual Loops

rust
// Good: Declarative, lazy, composablelet active_emails: Vec<String> = users.iter()    .filter(|u| u.is_active)    .map(|u| u.email.clone())    .collect();
// Bad: Imperative accumulationlet mut active_emails = Vec::new();for user in &users {    if user.is_active {        active_emails.push(user.email.clone());    }}

Use collect() with Type Annotation

rust
// Collect into different typeslet names: Vec<_> = items.iter().map(|i| &i.name).collect();let lookup: HashMap<_, _> = items.iter().map(|i| (i.id, i)).collect();let combined: String = parts.iter().copied().collect();
// Collect Results — short-circuits on first errorlet parsed: Result<Vec<i32>, _> = strings.iter().map(|s| s.parse()).collect();

Concurrency

Arc<Mutex<T>> for Shared Mutable State

rust
use std::sync::{Arc, Mutex};
let counter = Arc::new(Mutex::new(0));let handles: Vec<_> = (0..10).map(|_| {    let counter = Arc::clone(&counter);    std::thread::spawn(move || {        let mut num = counter.lock().expect("mutex poisoned");        *num += 1;    })}).collect();
for handle in handles {    handle.join().expect("worker thread panicked");}

Channels for Message Passing

rust
use std::sync::mpsc;
let (tx, rx) = mpsc::sync_channel(16); // Bounded channel with backpressure
for i in 0..5 {    let tx = tx.clone();    std::thread::spawn(move || {        tx.send(format!("message {i}")).expect("receiver disconnected");    });}drop(tx); // Close sender so rx iterator terminates
for msg in rx {    println!("{msg}");}

Async with Tokio

rust
use tokio::time::Duration;
async fn fetch_with_timeout(url: &str) -> Result<String> {    let response = tokio::time::timeout(        Duration::from_secs(5),        reqwest::get(url),    )    .await    .context("request timed out")?    .context("request failed")?;
    response.text().await.context("failed to read body")}
// Spawn concurrent tasksasync fn fetch_all(urls: Vec<String>) -> Vec<Result<String>> {    let handles: Vec<_> = urls.into_iter()        .map(|url| tokio::spawn(async move {            fetch_with_timeout(&url).await        }))        .collect();
    let mut results = Vec::with_capacity(handles.len());    for handle in handles {        results.push(handle.await.unwrap_or_else(|e| panic!("spawned task panicked: {e}")));    }    results}

Unsafe Code

When Unsafe Is Acceptable

rust
// Acceptable: FFI boundary with documented invariants/// # Safety/// `ptr` must be a valid, aligned pointer to an initialized `Widget`.unsafe fn widget_from_raw<'a>(ptr: *const Widget) -> &'a Widget {    // SAFETY: caller guarantees ptr is valid and aligned    unsafe { &*ptr }}
// Acceptable: Performance-critical path with proof of correctness// SAFETY: index is always < len due to the loop boundunsafe { slice.get_unchecked(index) }

When Unsafe Is NOT Acceptable

rust
// Bad: Using unsafe to bypass borrow checker// Bad: Using unsafe for convenience// Bad: Using unsafe without a Safety comment// Bad: Transmuting between unrelated types

Module System and Crate Structure

Organize by Domain, Not by Type

text
my_app/├── src/│   ├── main.rs│   ├── lib.rs│   ├── auth/          # Domain module│   │   ├── mod.rs│   │   ├── token.rs│   │   └── middleware.rs│   ├── orders/        # Domain module│   │   ├── mod.rs│   │   ├── model.rs│   │   └── service.rs│   └── db/            # Infrastructure│       ├── mod.rs│       └── pool.rs├── tests/             # Integration tests├── benches/           # Benchmarks└── Cargo.toml

Visibility — Expose Minimally

rust
// Good: pub(crate) for internal sharingpub(crate) fn validate_input(input: &str) -> bool {    !input.is_empty()}
// Good: Re-export public API from lib.rspub mod auth;pub use auth::AuthMiddleware;
// Bad: Making everything pubpub fn internal_helper() {} // Should be pub(crate) or private

Tooling Integration

Essential Commands

bash
# Build and checkcargo buildcargo check              # Fast type checking without codegencargo clippy             # Lints and suggestionscargo fmt                # Format code
# Testingcargo testcargo test -- --nocapture    # Show println outputcargo test --lib             # Unit tests onlycargo test --test integration # Integration tests only
# Dependenciescargo audit              # Security auditcargo tree               # Dependency treecargo update             # Update dependencies
# Performancecargo bench              # Run benchmarks

Quick Reference: Rust Idioms

IdiomDescription
Borrow, don't clonePass &T instead of cloning unless ownership is needed
Make illegal states unrepresentableUse enums to model valid states only
? over unwrap()Propagate errors, never panic in library/production code
Parse, don't validateConvert unstructured data to typed structs at the boundary
Newtype for type safetyWrap primitives in newtypes to prevent argument swaps
Prefer iterators over loopsDeclarative chains are clearer and often faster
#[must_use] on ResultsEnsure callers handle return values
Cow for flexible ownershipAvoid allocations when borrowing suffices
Exhaustive matchingNo wildcard _ for business-critical enums
Minimal pub surfaceUse pub(crate) for internal APIs

Anti-Patterns to Avoid

rust
// Bad: .unwrap() in production codelet value = map.get("key").unwrap();
// Bad: .clone() to satisfy borrow checker without understanding whylet data = expensive_data.clone();process(&original, &data);
// Bad: Using String when &str sufficesfn greet(name: String) { /* should be &str */ }
// Bad: Box<dyn Error> in libraries (use thiserror instead)fn parse(input: &str) -> Result<Data, Box<dyn std::error::Error>> { todo!() }
// Bad: Ignoring must_use warningslet _ = validate(input); // Silently discarding a Result
// Bad: Blocking in async contextasync fn bad_async() {    std::thread::sleep(Duration::from_secs(1)); // Blocks the executor!    // Use: tokio::time::sleep(Duration::from_secs(1)).await;}

Remember: If it compiles, it's probably correct — but only if you avoid unwrap(), minimize unsafe, and let the type system work for you.

Source and attribution

Source:affaan-m/ECCin.kiro/skills/rust-patternsat commitef648e0

License: No license

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