Weekly Review — Month 1 · Week 4 (Days 022–028)¶

Journal index · Roadmap › Week 4

📅 The Week in One Line¶

Composed types with embedding, generalized algorithms with generics and generic containers, and tied it all together in a tested, zero-dependency CLI (taskcli) — closing out Month 1.

✅ What I Completed¶

Day 022 — Struct embedding & composition (promotion, shadowing, interface embedding)
Day 023 — Generics fundamentals (type params, any/comparable/cmp.Ordered/unions, inference)
Day 024 — Generic data structures: Stack[T] & Set[T]
Day 025 — Project: Task model + atomic JSON store
Day 026 — Project: subcommands & flags via stdlib flag
Day 027 — Project: table-driven tests (t.TempDir) + README
Day 028 — Week 4 + Month 1 review; tag v0.1.0
Runnable examples: embedding, generics, generic-ds, cli-flags
Exercises solved: 3 (genslice, genstack, genset) — all table-driven, green

💡 Lessons Learned¶

Embedding is composition, not inheritance: members are promoted (auto-forwarded), but there's no subtyping and no virtual dispatch. The outer type shadows promoted members of the same name.
Pick the weakest constraint that compiles: any for a pure container, comparable for map-keyed sets, cmp.Ordered only when you compare with </>. Unions need ~ to accept named types.
Generics shine when the algorithm is identical across types; switch to an interface when behavior differs by type. They're complements, not competitors.
Generic "empty" returns must use var zero T — you can't write nil/0 for an arbitrary T.
Treat a missing data file as an empty store, not an error (errors.Is(err, os.ErrNotExist)); save atomically with temp-file + os.Rename so a crash never corrupts data.
Keep main a one-liner over run([]string) error: testable, and os.Exit (which skips defers) stays at the top level only.
t.TempDir() + table-driven subtests make file-backed code easy to test with zero cleanup; assert error paths with errors.Is, never string compares.

💪 Strengths (what clicked)¶

Reading and writing generic signatures, and choosing generics vs interfaces deliberately.
Building small, well-tested containers; the flag subcommand pattern.

🧩 Weaknesses (what's still fuzzy)¶

Reflex to choose cmp.Ordered vs comparable under time pressure.
Remembering ~ in union constraints for named types.
Method-set subtleties when embedding pointer vs value types.

🔁 Spaced-Repetition Re-quiz (topics from earlier weeks)¶

Q: (Wk2) Why can append mutate a slice you passed in, and how do you avoid it?
A
Slices share a backing array; if append has spare cap it writes in place, aliasing the caller's data. Copy first (append([]T(nil), s...)) or full-slice s[a:b:b] to force a new array.
Q: (Wk3) A function returns error; a typed nil *MyErr is assigned to it. Is the result == nil?
A
No — the interface holds a non-nil type with a nil value, so it's non-nil. Return literal nil for success.
Q: (Wk1) What does iota equal on the third ConstSpec line of a const block?
A
2 — it starts at 0 and increments by one per line in the block.
Q: (Wk3) Which is in the method set of T (value): value-receiver methods, pointer-receiver methods, or both?
A
Only value-receiver methods. *T's method set includes both. An addressable T can still call pointer methods via auto-&, but the method set of T itself excludes them.

🎯 Action Items¶

Add a one-page "generics vs interfaces" decision note to the cheatsheets.
Drill the comparable vs cmp.Ordered distinction in flashcards.
Re-implement Stack[T]/Set[T] from scratch, closed-book, once next week.
Replace hand-rolled helpers with slices/maps stdlib in a refactor pass.

🚀 Next Week Goals¶

Begin Month 2 (Concurrency & the runtime): goroutines, channels, select, sync primitives, and context.
Carry the run() error + table-driven testing discipline into concurrent code (add -race).
Extend taskcli ideas toward a concurrent/server variant later in the month.

📊 Metrics¶

Hours	Days hit	Exercises	Commits	Avg confidence
10	7/7	3	9	3.⅘

Suggested commit: docs(journal): week 4 review