Test — Module 15: Reflection and Metaprogramming¶

Topic: [[go]] Module: [[go/15. Reflection and Metaprogramming]]

Before You Begin¶

[!WARNING] Do not look at ANSWERS.md or your notes during the test. The purpose of this test is to surface what you truly know vs. what you think you know. An inflated score is worthless. An honest score shows you exactly where to focus next.

Instructions: 1. Close all notes, the module README, and any reference materials. 2. Set a timer. Note your start time below. 3. Attempt every question — partial credit exists. 4. After finishing, grade yourself using ANSWERS.md. 5. Record your score in the Grading Record at the bottom.

Start time: ___________ End time: ___________ Total time: ___________

Scoring Table¶

Passing score: 15/22 (68%)  ·  Target score: 18/22 (82%)

Section 1: Recall (5 questions × 1 pt = 5 pts)¶

Quick recall questions. Answer from memory in 1–3 sentences each.

1.1 What does reflect.TypeOf(x) return, and what does reflect.ValueOf(x) return? How are they different?

Your answer:

1.2 State the Third Law of Reflection in your own words. What concrete requirement must be met for a reflect.Value to be settable?

Your answer:

1.3 What is the difference between a value's reflect.Type and its reflect.Kind? Give a concrete example where the Type and Kind are different strings.

Your answer:

1.4 What method on reflect.StructField do you call to retrieve a struct tag value for a specific key (e.g., "json")? What does it return if the key is absent?

Your answer:

1.5 What is go generate? What does the //go:generate directive do, and when is it executed?

Your answer:

Section 2: Conceptual Understanding (3 questions × 2 pts = 6 pts)¶

Demonstrate that you understand the "why", not just the "what".

2.1 Explain why you must pass a pointer and call .Elem() to modify a struct's fields via reflection. What happens if you pass the struct directly (not a pointer) and try to call SetInt on one of its fields?

Your answer:

2.2 encoding/json uses reflection to marshal and unmarshal structs. Explain at least two things it does using struct tags — specifically, what information does it extract from the json struct tag, and how does it use each piece?

Your answer:

2.3 Compare reflection and generics as tools for writing code that works across multiple types. For each approach, describe one situation where it is clearly the better choice, and explain why the other approach would be worse in that situation.

Your answer:

Section 3: Applied / Practical (2 questions × 3 pts = 6 pts)¶

Show that you can use your knowledge to solve real problems.

3.1 Write a complete Go function PrintStructFields(v interface{}) that: - Accepts any struct (or pointer to struct) - Iterates over all exported fields - Prints each field's name, its reflect.Kind, and its current value - Handles both T and *T input (normalizes pointers) - Does not panic for non-struct input (print a message and return)

Show how you would call it with a Person{Name: "Alice", Age: 30} struct.

Your answer:

3.2 Write a complete Go function ZeroFields(ptr interface{}, names ...string) that: - Takes a pointer to any struct plus a list of field names to zero out - For each named field, if it exists and is settable, sets it to its zero value using reflect.Zero(field.Type()) - Returns an error (not a panic) if ptr is not a pointer to a struct

Your answer:

Section 4: Scenario / Debugging (1 question × 3 pts = 3 pts)¶

Analyze a realistic scenario and identify what's wrong or what should be done.

4.1 A colleague writes the following code intending to update a configuration struct via reflection:

type AppConfig struct {
    MaxWorkers int
    LogLevel   string
    verbose    bool // unexported
}

func updateConfig(cfg AppConfig) {
    v := reflect.ValueOf(cfg)
    v.FieldByName("MaxWorkers").SetInt(8)    // line A
    v.FieldByName("LogLevel").SetString("debug") // line B
    v.FieldByName("verbose").SetBool(true)   // line C
}

Identify:

a) What is wrong with this code? How many distinct bugs are present? List each one.

b) For each bug, explain why it causes a panic (or incorrect behavior) rather than a compile error.

c) Rewrite updateConfig correctly. It should update MaxWorkers and LogLevel, skip verbose gracefully, and not panic.

Your answer:

Section 5: Essay / Discussion (1 question × 2 pts = 2 pts)¶

Open-ended. There is more than one good answer. Show your reasoning.

5.1 "Reflection is a powerful tool, but it should be used sparingly in Go." Do you agree or disagree? Discuss the specific costs of reflection (not just "it's slow") and describe the decision process you would use to choose between reflection, generics, interfaces, and go generate when writing a library that needs to handle arbitrary user-defined types.

Consider at least two concrete scenarios in your answer — one where you would reach for reflection and one where you would not.

Your answer (aim for 4–8 sentences):

Section 6: Bonus Challenge (1 question × +5 pts)¶

[!NOTE] This question is optional. It will not count against you if you skip it or get it wrong. Only attempt it after completing Sections 1–5.

6.1 Implement a function DeepCopy(src interface{}) interface{} that uses reflection to create a deep copy of any struct (not pointer to struct). The copy should: - Be a new allocation with the same type as src - Have all exported fields copied by value - Handle nested structs recursively (i.e., if a field is itself a struct, deep copy it too) - Return the copy as interface{}

Show that modifying a field in the copy does not affect the original, and vice versa. You do not need to handle slices, maps, pointers, or channels — only flat and nested structs with scalar fields.

Bonus points for also handling slice fields (making a new slice with copied elements).

Your answer:

Self-Assessment¶

After grading your test, answer these questions honestly:

What did I get right and why?

Your reflection:

What did I get wrong and why did I make that mistake?

Your reflection:

What should I review before moving to the next module?

Your reflection:

What score did I get? Do I feel it accurately reflects my understanding?

Your reflection:

Grading Record¶

Append a new row each time you take this test. Do not overwrite previous attempts.

Grade scale: A ≥ 90% (≥20/22)  ·  B ≥ 80% (≥18/22)  ·  C ≥ 70% (≥15/22)  ·  D ≥ 60% (≥13/22)  ·  F < 60%

See ANSWERS.md for the answer key. Review it only after completing the test.