go-quiz.md

Go (Programming Language)

Q1. What do you need for two functions to be the same type?

• They should share the same signatures, including parameter types and return types.
• They should share the same parameter types but can return different types.
• All functions should be the same type.
• The functions should not be a first class type.

Explanation: User defined function types in Go (Golang)

Q2. What does the len() function return if passed a UTF-8 encoded string?

• the number of characters
• the number of bytes
• It does not accept string types.
• the number of code points

Explanation: Length of string in Go (Golang).

Q3. Which is not a valid loop construct in Go?

• do { ... } while i < 5
• for _,c := range "hello" { ... }
• for i := 1; i < 5; i++ { ... }
• for i < 5 { ... }

Explanation: Go has only for-loops

Q4. How will you add the number 3 to the right side?

values := []int{1, 1, 2}

• values.append(3)
• values.insert(3, 3)
• append(values, 3)
• values = append(values, 3)

Explanation: slices in GO are immutable, so calling append does not modify the slice

Q5. What is the value of Read?

const (
  Write = iota
  Read
  Execute
)

• 0
• 1
• 2
• a random value

Reference: IOTA in Go (Golang)

Q6. Which is the only valid import statement in Go?

• import "github/gin-gonic/gin"
• import "https://github.com/gin-gonic/gin"
• import "../template"
• import "github.com/gin-gonic/gin"

Reference: Import in GoLang

Q7. What would happen if you attempted to compile and run this Go program?

package main
var GlobalFlag string
func main() {
  print("["+GlobalFlag+"]")
}

• It would not compile because GlobalFlag was never initialized.
• It would compile and print [].
• It would compile and print nothing because "[" +nil+"]" is also nil.
• It would compile but then panic because GlobalFlag was never initialized.

Explanation: most variables in Go has initial values. For string type it's an empty string.

Here is this program on Go Playground

Q8. From where is the variable myVar accessible if it is declared outside of any functions in a file in package myPackage located inside module myModule?

• It can be accessed anywhere inside myPackage, not the rest of myModule.
• It can be accessed by any application that imports myModule.
• It can be accessed from anywhere in myModule.
• It can be accessed by other packages in myModule as long as they import myPackage

Explanation: to make the variable available outside of myPackage change the name to MyVar. See also an example of Exported names in the Tour of Go.

Q9. How do you tell go test to print out the tests it is running?

• go test
• go test -x
• go test --verbose
• go test -v

Reference: test package

Q10. This code printed {0, 0}. How can you fix it?

type Point struct {
  x int
  y int
}

func main() {
  data := []byte(`{"x":1, "y": 2}`)
  var p Point
  if err := json.Unmarshal(data, &p); err != nil {
    fmt.Println("error: ", err)
  } else {
    fmt.Println(p)
  }
}

• use json.Decoder
• Pass a pointer to data
• Make X and Y exported (upercase)
• Use field tags

Reference: How to Parse JSON in Golang?

Fixed version on Go Playground

Q11. What does a sync.Mutex block white it is locked?

• all goroutines
• any other call to lock that Mutex
• any reads or writes of the variable it is locking
• any writes to the variable it is locking

Reference: Mutex in GoLang

Q12. What is an idiomatic way to pause execution of the current scope until an arbitrary number of goroutines have returned?

• Pass an int and Mutex to each and count when they return.
• Loop over a select statement.
• Sleep for a safe amount of time.
• sync.WaitGroup

Explanation: this is exactly what sync.WaitGroup is designed for - Use sync.WaitGroup in Golang

Q13. What is a side effect of using time.After in a select statement?

• It blocks the other channels.
• It is meant to be used in select statements without side effects.
• It blocks the select statement until the time has passed.
• The goroutine does not end until the time passes.

Note: it doesn't block select and does not block other channels.

Q14. What is the select statement used for?

• executing a function concurrently
• executing a different case based on the type of a variable
• executing a different case based on the value of a variable
• executing a different case based on which channel returns first

Q15. According to the Go documentation standard, how should you document this function?

func Add(a, b int) {
  return a + b
}

• A

// Calculate a + b
// - a: int
// - b: int
// - returns: int
func Add(a, b int) {
  return a + b
}

• B

// Does a + b
func Add(a, b int) {
  return a + b
}

• C

// Add returns the sum of a and b
func Add(a, b int) {
  return a + b
}

• D

// returns the sum of a and b
func Add(a, b int) {
  return a + b
}

Explanation: documentation block should start with a function name

Q16. What restriction is there on the type of var to compile this i := myVal.(int)?

• myVal must be an integer type, such as int, int64, int32, etc.
• myVal must be able to be asserted as an int.
• myVal must be an interface.
• myVal must be a numeric type, such as float64 or int64.

Explanation: This kind of type casting (using .(type)) is used on interfaces only. See this example for instance. Primitive types are type-casted differently - Type-casting in GoLang

Example on Go Playground

Q17. What is a channel?

• a global variable
• a medium for sending values between goroutines
• a dynamic array of values
• a lightweight thread for concurrent programming

Reference: Channels