Better vs worse

Each entry shows one small task, written two or three ways. The “Worse” version is code that an AI agent could produce: it compiles, it passes a simple test, and it looks reasonable. The “OK” version is acceptable. The “Better” version is what a reviewer would ask for.

Every version is real code in the examples/better-vs-worse crate. Its tests show how the versions differ, for example a test that proves the “Worse” version panics.

How to read an entry

Each entry has:

• The task, in one sentence.
• The versions, labeled Worse, OK, and Better.
• A verdict table. Each version is compared with the Worse version for correctness, failure behavior, performance, readability, and API ergonomics. The scale is Better, Same, or Worse.
• Trade-offs: when the “Worse” version is acceptable. There is almost always a case.
• Related smells and concepts.

Use it as practice

Before you read the explanation, look at the Worse version and write down what you would say in a review. Then compare.

Entries

1. Read a config fileRead a config file and parse it: unwrap vs ? with context vs a typed error.
2. Find a user by IDFind a user by ID in a list: a panic and a copy vs Option vs Option<&User>.
3. Count wordsCount words in a text: contains_key and insert vs the HashMap entry API.
4. Process a list of ordersTurn orders into invoices: clone vs borrow vs into_iter.
5. Model a payment stateA string status vs bool flags vs an enum.
6. A shape hierarchyAn abstract-class translation vs trait objects vs an enum.
7. Build a request with optional fieldsnew with eight parameters vs a builder vs Default with struct update.
8. Share a cache between threadsArc<Mutex<HashMap>> vs RwLock vs a concurrent map vs message passing.Not written yet.
9. Fetch three URLsSequential await vs join! vs a blocking client in async code.Not written yet.
10. Parse numbers from inputas casts vs try_from vs parse with typed errors.
11. A linked or tree structureRc<RefCell> vs Box vs an arena with indices.
12. Return a collectionVec vs impl Iterator vs a slice.
13. Read a large fileRead all into a String vs BufReader::lines.
14. Error types for a libraryString vs Box<dyn Error> vs a thiserror enum.