Day 014 — Week 2 Review Day

Month 1 · Week 2 · ⬅ Day 013 · Day 015 ➡ · Journal index

📋 Full structured review: week-2-review.md

🎯 Learning Objective

Consolidate Week 2 (composite types) via closed-book recall and clean up the week's code.

📚 Topics

• Recap: arrays/slices (len/cap), append & aliasing, slice tricks, maps/sets, strings/runes, structs & tags.

📝 Notes

• Re-ran every Week 2 example with go run; ran go test ./... (wordfreq, dedup, runereverse all green).
• Ran gofmt -l . and go vet ./... — formatting clean, no vet findings.
• Redid the dedup and rune-reverse exercises from memory (active recall) — passed first try.

🧠 Closed-Book Recall (Week 2)

1. Q: What does a slice header contain?
   A

Pointer to backing array, length, capacity. 2. Q: When does append reallocate?

A

When capacity is exhausted; otherwise it writes in place into the shared backing array.

3. Q: How do you cap a slice's capacity to prevent aliasing?

A

The 3-index slice s[low:high:max], e.g. s[i:j:j].

4. Q: Order-preserving delete of index i?

A

s = append(s[:i], s[i+1:]...).

5. Q: Reading a missing map key gives you what?

A

The value type's zero value; use comma-ok to detect absence.

6. Q: Why is map iteration order randomized?

A

Intentionally, so code can't depend on it; sort keys for stable output.

7. Q: Bytes vs runes for len("héllo")?

A

len = 6 bytes; 5 runes.

8. Q: What does json:"-" do on a field?

A

Excludes it from JSON entirely (never marshaled/unmarshaled).

🐛 Mistakes / Themes This Week

• The append aliasing trap (Day 009) — the week's biggest gotcha.
• Nil-map writes panicking (Day 011).
• Reversing strings by byte instead of rune (Day 012).

🪶 Feynman Reflection

Composite types are all about views over memory: slices view arrays, maps key-address values, strings are byte ribbons, and structs bundle fields. Knowing what is shared vs copied is the whole game.

🕳️ Knowledge Gaps Carried Forward

• The slices/maps stdlib helper packages — adopt actively next week.
• Methods, interfaces, and the nil-interface trap (Week 3 headline).

✅ Summary

Week 2 composite types consolidated; all code formatted, vetted, and tested. Confidence on slices/maps/strings/structs now ⅘.

⏭️ Next Steps

• Week 3: methods & receivers, interfaces (implicit satisfaction, nil-interface trap), and error handling.

---

Time spent	Difficulty	Confidence
75 min	🟦⬜⬜⬜⬜	🟦🟦🟦🟦⬜

Suggested commit: docs(journal): week 2 review (day 014)