Rust Standard Library — API Selection and Composition

Authority: Rust Standard Library — the canonical reference. Read references/std-module-index.md for the full module map.

This skill owns choosing and composing std APIs: which collection, which smart pointer, which string type, which I/O trait, which iterator pattern. It does not own language semantics (rust-stable), async runtime (rust-concurrency), or application-layer concerns (the domain skills).

Capability Boundaries

✅ Strengths

1. Picking the right collection (HashMap vs BTreeMap vs Vec vs VecDeque vs LinkedList vs BinaryHeap)
2. Choosing the right smart pointer (Box vs Rc vs Arc vs RefCell vs Mutex vs OnceLock)
3. Selecting the right string type (String vs &str vs OsString vs PathBuf vs Cow)
4. Choosing interior mutability primitive (Cell vs RefCell vs OnceCell vs OnceLock vs LazyLock)
5. Designing Option/Result combinator chains (map, and_then, unwrap_or_else, ok_or, transpose)
6. Selecting I/O trait (Read vs Write vs BufRead vs Seek vs AsyncRead)
7. Choosing iterator pattern (iter vs into_iter vs owning iterator, lazy vs collect)
8. Using std concurrency primitives (thread, mpsc, barrier, Once, scoped threads)
9. Selecting time API (Duration vs Instant vs SystemTime vs TryFromFloat)
10. Cross-platform path handling (Path vs PathBuf, fs, env, process::Command)