Go Quiz — CodeAtlas Go Course

1. What happens if a Go file imports a package it never uses?

Nothing; unused imports are ignored
The compiler prints a warning
The program doesn't compile
The import is removed at run time

2. Which command runs the package in the current folder of a module?

go start
go exec main.go
go run .
go build --run

3. What is the zero value of a string variable?

nil
"" (the empty string)
"0"
It has no value until assigned

4. What does len("Café") return?

4
5
8
It depends on the operating system

len counts bytes, and é takes two bytes in UTF-8 (lessons 07 and 19).

5. What does 7 / 2 evaluate to when both operands are int?

3.5
3
4
A compile error

6. What do the constants in const ( A = iota; B; C ) equal?

1, 2, 3
0, 1, 2
All 0
A compile error: B and C have no value

iota starts at 0 and the expression is repeated for B and C (lesson 10).

7. Why does string(65) usually indicate a bug?

It panics
It returns "65"
It returns "A", the character with code point 65 — use strconv.Itoa for digits
It doesn't compile

go vet reports this conversion (lesson 09).

8. In a Go switch, what happens after a matching case's code runs?

The switch ends; there's no fall-through unless you write fallthrough
Execution continues into the next case
You must write break or the next case runs
The default case runs too

9. How does Go write a "while" loop?

while cond { }
loop while cond { }
for cond { }
do { } while (cond)

for is Go's only loop keyword (lesson 16).

10. When you range over a map, in what order are the entries visited?

Insertion order
Sorted by key
An unspecified order that can change from run to run
Reverse insertion order

Sort the keys, for example with slices.Sorted(maps.Keys(m)), when order matters (lesson 17).

11. a := []int{1, 2, 3}; b := a[0:2]; b[0] = 9 — what is a now?

[1 2 3]
[9 2 3]
[9 2]
A compile error

12. Why must you write s = append(s, x) instead of just append(s, x)?

Because append has no side effects at all
Because append may allocate a new array and returns the updated slice header
It's only a style rule
Because slices are immutable

13. What does writing to a key of a nil map do?

Creates the map automatically
Nothing
Panics
Returns an error

Reading a nil map is fine, writing panics; create maps with make or a literal (lesson 28).

14. In what order do several deferred calls in one function run?

In the order they were deferred
Last in, first out
In random order
Only the last one runs

15. When are the arguments of a deferred call evaluated?

When the defer statement runs
When the surrounding function returns
When the deferred call starts
Never; deferred calls take no arguments

16. What does a method with a value receiver, func (c Counter) Inc(), change when it does c.n++?

The caller's Counter
A copy, so the caller sees no change
Nothing; it doesn't compile
Every Counter in the program

17. How does a type declare that it implements an interface?

With the implements keyword
By embedding the interface
It doesn't need to; having the methods is enough
By registering it in init

18. A function returns error and ends with var e *MyErr; return e. What does err == nil give the caller?

true
false, because the interface holds a typed nil pointer
It panics
It doesn't compile

Return a literal nil for "no error" (lesson 40).

19. Which is the safe way to check whether v any holds a string?

s := v.(string)
s, ok := v.(string)
s := string(v)
if v is string

20. What makes a name visible to other packages?

The public keyword
Listing it in an export block
Starting it with a capital letter
Putting it in a file named export.go

21. What does fmt.Errorf("loading: %w", err) do that %v doesn't?

It prints the error in red
It wraps err so errors.Is and errors.AsType can still find it
It panics if err is nil
Nothing; they're identical

22. When is it appropriate to use panic?

For any error
For invalid user input
For bugs and impossible situations, such as a broken invariant
To return early from a function

23. What does the constraint in func Index[T comparable](s []T, v T) int allow?

Using < on values of T
Using == and != on values of T
Only built-in types
Calling methods on T

24. What's new about methods in Go 1.27?

Methods can be declared inside functions
A method can declare its own type parameters
Interface methods can be generic
Methods can be overloaded

25. In a range-over-func iterator, what should the iterator do when yield returns false?

Call yield again
Panic
Stop and return, because the loop body has exited
Restart from the beginning

26. What happens to running goroutines when main returns?

main waits for them automatically
The program exits and they're stopped
They keep running in the background
They are moved to a new process

Use sync.WaitGroup or channels to wait (lesson 51).

27. Who should close a channel?

The sender, once it has no more values to send
The receiver, once it has read everything
Any goroutine
Nobody; channels close themselves

28. How do you detect data races in Go?

With go vet -threads
By running with -race, e.g. go test -race ./...
They're impossible in Go
With go fmt

29. Which date layout produces 2026-10-08?

"YYYY-MM-DD"
"%Y-%m-%d"
"2006-01-02"
"2026-10-08"

30. What must an HTTP client do with every response it receives?

Nothing
Call resp.Wait()
Close resp.Body
Check that the status is 200, or the program panics