Test — Module 5: Pointers¶

Topic: [[go]] Module: [[go/5. Pointers]]

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 the & operator do in Go? Give a one-line example showing its use with a variable.

Your answer:

1.2 What is the zero value of any pointer type in Go? What happens at runtime if you dereference that zero value?

Your answer:

1.3 What is the difference between new(T) and &T{}? When would you prefer one over the other?

Your answer:

1.4 If p is *Point and Point has a field X float64, how do you read and write the X field through p? Do you need to write (*p).X, or is there a shorter form?

Your answer:

1.5 Go passes all function arguments by value. Given this, explain in one sentence why a function receiving *MyStruct can modify the caller's struct, even though the pointer itself is passed by value.

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 Go's "call-by-value" model, and walk through what happens in memory when you call update(p *Person) vs update(p Person). Why does the pointer version allow mutation and the value version does not? Be specific about what is copied in each case.

Your answer:

2.2 A colleague says: "I always pass maps as *map[K]V to functions that modify them, to make sure the changes are visible to the caller." Is this correct? What do they have right, and what do they have wrong? Explain what a map value actually is under the hood.

Your answer:

2.3 Explain escape analysis in your own words. Why is it safe in Go to return the address of a local variable (return &x) — something that would be undefined behavior in C? What does the compiler do to make this safe, and what is the runtime cost?

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 program that: - Defines a struct BankAccount with Owner string and Balance float64 - Writes a function deposit(a *BankAccount, amount float64) that adds amount to a.Balance - Writes a function withdraw(a *BankAccount, amount float64) error that subtracts amount if sufficient funds exist, or returns an error - In main, creates an account, deposits 200.00, withdraws 50.00, attempts to withdraw 500.00 (expecting an error), and prints the final balance

Your answer:

3.2 Write a function findFirst(s []int, pred func(int) bool) *int that returns a pointer to the first element in s satisfying pred, or nil if no element qualifies. Then write a main that calls it with []int{4, 7, 2, 9, 1} and pred = "is odd", prints the value if found, and handles the nil case.

Note: returning &s[i] for a slice element is valid Go.

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 developer writes the following code to count words in a slice of strings. The intent is to use a shared counter that both countWords and main can see:

func countWords(words []string, count int) {
    for _, w := range words {
        if len(w) > 0 {
            count++
        }
    }
}

func main() {
    words := []string{"hello", "world", "", "go"}
    total := 0
    countWords(words, total)
    fmt.Println("Total:", total)  // prints 0, expected 3
}

Identify:

a) What is wrong with this code? Trace what happens to count and total.

b) Why does this happen? Name the Go feature that causes it.

c) Fix the code. Show the corrected countWords signature and any changes to main. Give two valid fixes: one using a pointer argument, one using a return value.

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 "In Go, you should use pointers sparingly — only when you have a specific reason to. The default should be to pass values." Do you agree with this statement? Argue for or against it, covering at least three of the following considerations: mutation intent, struct size, reference-like types (slices/maps), optional/nullable values, and the impact on garbage collection.

Consider the perspective of a developer reading your API: what does passing a pointer vs a value communicate about ownership and mutation intent?

Your answer (aim for 3–6 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 generic Set[T comparable] type as a struct wrapping a map[T]struct{}. Provide three methods: Add(value T), Contains(value T) bool, and Size() int. All methods should use pointer receivers (*Set[T]) where appropriate and value receivers where that is preferable. Write a main function demonstrating the set with int values.

Then explain: why should Add use a pointer receiver but Contains and Size could use either? What rule guides this decision, and how does it connect to what you learned about pointer semantics in this module?

(This question previews [[go/6. Methods and Interfaces]] and [[go/10. Generics]] — use your best reasoning even if you haven't studied those modules yet.)

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.