rust-best-practices

Return Result<T, E> for fallible operations and avoid unwrap or expect in production code. Use thiserror for library error types with #[from] conversions, anyhow only for binaries, and the ? operator to propagate errors instead of match chains.

Prefer borrowing with &T over .clone() unless ownership transfer is required, such as caching results, sharing across threads with Arc, or API designs requiring owned data. Use &str over String and &[T] over Vec<T> in function parameters, and consider Cow for ambiguous ownership.

Run cargo clippy --all-targets --all-features --locked -- -D warnings regularly. Key lints include redundant_clone, large_enum_variant, needless_collect, and clone_on_copy. Configure workspace lints in Cargo.toml and use #[expect] with justification instead of #[allow].

Prefer generics with static dispatch for performance-critical code since monomorphization has zero runtime cost. Use dyn Trait only when you need heterogeneous collections, plugin architectures, or runtime polymorphism, and box at API boundaries rather than internally.

Name tests descriptively like process_should_return_error_when_input_empty, keep one assertion per test, and organize related tests in modules. Use doc tests for public API examples and cargo insta for snapshot testing of generated output or serialized data.

Avoid type state for trivial states that enums handle fine, when runtime flexibility is required, or when it leads to overcomplicated generics and verbose duplication. Use it when compile-time state safety prevents real bugs, such as enforcing builder field completion or protocol ordering.