Rust

Write idiomatic Rust avoiding ownership pitfalls, lifetime confusion, and common borrow checker battles.

Security Scan

This is a documentation-only skill that gives Rust guidance and does not request unrelated credentials, install external code, or perform unexpected actions — its requirements match its stated purpose.

Purpose & Capability

Name/description (Rust guidance) align with requirements: it declares rustc and cargo as required binaries, which is appropriate for a Rust authoring helper.

Instruction Scope

SKILL.md and the included docs are purely educational guidance about ownership, lifetimes, errors, concurrency, etc.; they do not instruct the agent to read unrelated files, exfiltrate data, call external endpoints, or perform privileged system changes.

Install Mechanism

No install spec and no code files to execute are present. Being instruction-only minimizes the risk of downloading or running arbitrary code.

Credentials

The skill requests no environment variables, credentials, or config paths — nothing disproportionate to the stated purpose.

Persistence & Privilege

always is false and the skill does not request permanent or elevated privileges. Autonomous invocation is allowed by default on the platform but there are no additional privilege escalations requested by the skill.

Assessment

This skill is an instruction-only Rust reference and appears internally consistent. If you install it, ensure that the agent runs in an environment where rustc and cargo are legitimate system binaries you trust (the skill declares those as required). Because it can be invoked by the agent, be aware the agent might use local rust tooling when generating or checking code — if you run agents in a restricted environment, keep those restrictions in place. No credentials, downloads, or external endpoints are requested by this skill.

Quick Reference

Topic	File	Key Trap
Ownership & Borrowing	ownership-borrowing.md	Move semantics catch everyone
Strings & Types	types-strings.md	String vs &str, UTF-8 indexing
Errors & Iteration	errors-iteration.md	unwrap() in production, lazy iterators
Concurrency & Memory	concurrency-memory.md	Rc not Send, RefCell panics
Advanced Traps	advanced-traps.md	unsafe, macros, FFI, performance

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Critical Traps (High-Frequency Failures)

Ownership — #1 Source of Compiler Errors

• Variable moved after use — clone explicitly or borrow with &
• for item in vec moves vec — use &vec or .iter() to borrow
• String moved into function — pass &str for read-only access

Borrowing — The Borrow Checker Always Wins

• Can't have &mut and & simultaneously — restructure or interior mutability
• Returning reference to local fails — return owned value instead
• Mutable borrow through &mut self blocks all access — split struct or RefCell

Lifetimes — When Compiler Can't Infer

• 'static means CAN live forever, not DOES — String is 'static capable
• Struct with reference needs <'a> — struct Foo<'a> { bar: &'a str }
• Function returning ref must tie to input — fn get<'a>(s: &'a str) -> &'a str

Strings — UTF-8 Surprises

• s[0] doesn't compile — use .chars().nth(0) or .bytes()
• .len() returns bytes, not chars — use .chars().count()
• s1 + &s2 moves s1 — use format!("{}{}", s1, s2) to keep both

Error Handling — Production Code

• unwrap() panics — use ? or match in production
• ? needs Result/Option return type — main needs -> Result<()>
• expect("context") > unwrap() — shows why it panicked

Iterators — Lazy Evaluation

• .iter() borrows, .into_iter() moves — choose carefully
• .collect() needs type — collect::<Vec<_>>() or typed binding
• Iterators are lazy — nothing runs until consumed

Concurrency — Thread Safety

• Rc is NOT Send — use Arc for threads
• Mutex lock returns guard — auto-unlocks on drop, don't hold across await
• RwLock deadlock — reader upgrading to writer blocks forever

Memory — Smart Pointers

• RefCell panics at runtime — if borrow rules violated
• Box for recursive types — compiler needs known size
• Avoid Rc<RefCell<T>> spaghetti — rethink ownership

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Common Compiler Errors (NEW)

Error	Cause	Fix
value moved here	Used after move	Clone or borrow
cannot borrow as mutable	Already borrowed	Restructure or RefCell
missing lifetime specifier	Ambiguous reference	Add <'a>
the trait bound X is not satisfied	Missing impl	Check trait bounds
type annotations needed	Can't infer	Turbofish or explicit type
cannot move out of borrowed content	Deref moves	Clone or pattern match

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Cargo Traps (NEW)

• cargo update updates Cargo.lock, not Cargo.toml — manual version bump needed
• Features are additive — can't disable a feature a dependency enables
• [dev-dependencies] not in release binary — but in tests/examples
• cargo build --release much faster — debug builds are slow intentionally