Test — Module 10: Generics¶

Topic: [[go]] Module: [[go/10. Generics]]

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 Go version introduced generics, and in what year was it released?

Your answer:

1.2 What is the difference between the any constraint and the comparable constraint? When would you use each?

Your answer:

1.3 What does the ~ (tilde) operator mean in a constraint? For example, what is the difference between int and ~int in a union element?

Your answer:

1.4 Can a method on a generic type introduce a new type parameter? For example, is func (s *Stack[T]) Map[U any](f func(T) U) []U valid Go?

Your answer:

1.5 Name the three standard library packages added in Go 1.21 that use generics. What is the primary purpose of each?

Your answer:

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

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

2.1 Before Go 1.18, Go developers used two main approaches to write reusable code that worked across multiple types: interface{} with type assertions, and copy-paste per type. Explain the concrete problem with each approach and how generics solves both problems simultaneously.

Your answer:

2.2 Explain what "constraints are interfaces" means. How does a constraint differ from a plain interface used as a function parameter? Give an example where using a generic constraint is correct and an example where a plain interface is the better choice.

Your answer:

2.3 Explain Go's GC shape stenciling approach to implementing generics. How does it differ from C++'s full monomorphization? What are the practical performance implications for a Go developer using generics in production code?

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 generic function Keys[K comparable, V any](m map[K]V) []K that returns a slice of all keys in a map. Then write Values[K comparable, V any](m map[K]V) []V for values. Demonstrate both with a map[string]int containing at least three entries. (Note: map iteration order is non-deterministic — your output order may vary.)

Your answer:

3.2 Write a generic Stack[T any] type with Push, Pop (returning T, bool), and Len methods. Use it to implement a simple expression evaluator that processes a []string of tokens: for each token, if it's a number push it; if it's "+" pop two values and push their sum; print the final result. Use a Stack[int].

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 wrote the following generic function and is getting a compile error:

func FindMin[T any](s []T) T {
    if len(s) == 0 {
        return nil
    }
    min := s[0]
    for _, v := range s[1:] {
        if v < min {
            min = v
        }
    }
    return min
}

Identify all the errors in this function (there are at least two). For each error, explain:

a) What the error is and why it's a compile error (not just a runtime issue)

b) How to fix it

Write the corrected version of the function.

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 The Go blog post "When To Use Generics" identifies three scenarios where generics are appropriate and discourages their use in other cases. Summarize those three scenarios in your own words. Then give a concrete example from your own experience or imagination where you would reach for generics, and one where you would deliberately choose a plain interface instead. Explain your reasoning for each choice.

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 generic OrderedMap[K cmp.Ordered, V any] type that stores key-value pairs in sorted key order. It should support: - Set(key K, value V) — insert or update - Get(key K) (V, bool) — look up by key - Keys() []K — return all keys in sorted order - Values() []V — return all values in key-sorted order

The internal storage should use two parallel slices (keys []K, values []V) kept in sorted order. Set should maintain sorted order by finding the correct insertion point using binary search.

Demonstrate with OrderedMap[string, int] containing at least 5 entries added in non-alphabetical order, showing that Keys() returns them sorted.

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.