Rust Best Practices

Guidance for writing idiomatic, performant, and safe Rust code. This is a development skill, not a review skill -- use it when building, not reviewing.

Quick Reference

Topic	Key Rule	Reference
Ownership	Borrow by default, clone only when you need a separate owned copy	references/coding-idioms.md
Clippy	Run cargo clippy -- -D warnings on every commit; configure workspace lints	references/clippy-config.md
Performance	Don't guess, measure. Profile with --release first	references/performance.md
Generics	Static dispatch by default, dynamic dispatch when you need mixed types	references/generics-dispatch.md
Type State	Encode state in the type system when invalid operations should be compile errors	references/type-state-pattern.md
Documentation	// for why, /// for what and how, //! for module/crate purpose	references/documentation.md
Pointers	Choose pointer types based on ownership needs and threading model	references/pointer-types.md
API Design	Unsurprising, flexible, obvious, constrained -- encode invariants in types	references/api-design.md
Ecosystem	Evaluate crates, pick error handling strategy, stay current	references/ecosystem-patterns.md

Coding Idioms

Prefer

&T

over

.clone()

, use

&str

/

&[T]

in parameters, and chain iterators instead of index-based loops. For Option/Result, use

let Ok(x) = expr else { return }

for early returns and

?

for propagation. See references/coding-idioms.md for ownership, iterator, and import patterns.

Error Handling

Return

Result<T, E>

for fallible operations. Use

thiserror

for library error types,

anyhow

for binaries. Propagate with

?

, never

unwrap()

outside tests. See references/coding-idioms.md for Option/Result patterns.

Clippy Discipline

Run

cargo clippy --all-targets --all-features -- -D warnings

on every commit. Configure workspace lints in

Cargo.toml

and use

#[expect(clippy::lint)]

(not

#[allow]

) as the standard for lint suppression -- it warns when the suppression becomes stale. See references/clippy-config.md for lint configuration and key lints.

Performance Mindset

Always benchmark with

--release

, profile before optimizing, and avoid cloning in loops or premature

.collect()

calls. Keep small types on the stack and heap-allocate only recursive structures and large buffers. See references/performance.md for profiling tools and allocation guidance.

Generics and Dispatch

Use static dispatch (

impl Trait

/

<T: Trait>

) by default for zero-cost monomorphization. Switch to

dyn Trait

only for heterogeneous collections or plugin architectures, preferring

&dyn Trait

over

Box<dyn Trait>

when ownership isn't needed. In edition 2024,

-> impl Trait

captures all in-scope lifetimes by default -- use

+ use<'a, T>

for precise capture control. Prefer native

async fn

in traits over the

async-trait

crate for static dispatch. See references/generics-dispatch.md for dispatch trade-offs, RPIT capture rules, and async trait guidance.

Type State Pattern

Encode valid states in the type system so invalid operations become compile errors. Use for builders with required fields, protocol state machines, and workflow pipelines. See references/type-state-pattern.md for implementation patterns and when to avoid.

Documentation

Use

//

for why,

///

for what/how on public APIs, and

//!

for module purpose. Every

TODO

needs a linked issue and library crates should enable

#![deny(missing_docs)]

. Use

#[diagnostic::on_unimplemented]

to provide custom compiler errors for your public traits. See references/documentation.md for doc test patterns, comment conventions, and diagnostic attributes.

API Design

Follow four principles: unsurprising (reuse standard names and traits), flexible (use generics and

impl Trait

to avoid unnecessary restrictions), obvious (encode invariants in the type system so misuse is a compile error), and constrained (expose only what you can commit to long-term). Use

#[non_exhaustive]

for types that may grow, seal traits you need to extend without breaking changes, and wrap foreign types in newtypes to control your SemVer surface. See references/api-design.md for builder patterns, sealed traits, and SemVer implications.

Ecosystem Patterns

Evaluate crates by recent download trends, maintenance activity, documentation quality, and transitive dependency weight. Use

thiserror

for library error types,

anyhow

for binaries, and

eyre

when you need custom error reporters. Prefer vendoring or writing code yourself when a crate pulls heavy dependencies for a small feature. Run

cargo-deny

for license and vulnerability auditing and

cargo-udeps

to trim unused dependencies. See references/ecosystem-patterns.md for crate evaluation criteria, edition migration, and essential tooling.

Pointer Types

Choose pointer types based on ownership and threading:

Box<T>

for single-owner heap allocation,

Rc<T>

/

Arc<T>

for shared ownership,

Cell

/

RefCell

/

Mutex

/

RwLock

for interior mutability. Use

LazyLock

/

LazyCell

(stable since 1.80) instead of

lazy_static

or

once_cell

. See references/pointer-types.md for the full single-thread vs multi-thread decision table and migration guidance.