Value receivers in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method with value receiver

What is the output of this Go program?

Go

package main
import "fmt"
type Counter struct {
    count int
}
func (c Counter) Increment() {
    c.count++
}
func main() {
    c := Counter{count: 5}
    c.Increment()
    fmt.Println(c.count)
}

A Compilation error

B 6

C 0

D 5

💡 Hint

Think about whether the method changes the original struct or a copy.

The method Increment has a value receiver, so it works on a copy of the struct. The original count remains unchanged, so the output is 5.

❓ Predict Output

intermediate

Effect of value receiver on struct field

What will this program print?

Go

package main
import "fmt"
type Point struct {
    x int
}
func (p Point) Move() {
    p.x = 10
}
func main() {
    pt := Point{x: 5}
    pt.Move()
    fmt.Println(pt.x)
}

A 5

B 10

C 0

D Runtime panic

💡 Hint

Does the Move method change the original Point or a copy?

Move uses a value receiver, so it modifies a copy of pt. The original pt.x remains 5.

🔧 Debug

advanced

Why does this value receiver method not update the struct?

Consider this code snippet. Why does the field not update after calling Update()? package main import "fmt" type Data struct { value int } func (d Data) Update() { d.value = 100 } func main() { data := Data{value: 50} data.Update() fmt.Println(data.value) }

A Because Update has a value receiver and modifies a copy, not the original struct.

B Because the struct Data is immutable in Go.

C Because the Update method is missing a pointer receiver syntax.

D Because the field value is unexported and cannot be changed.

💡 Hint

Think about how value receivers work with struct copies.

Value receivers get a copy of the struct, so changes inside Update do not affect the original data variable.

📝 Syntax

advanced

Identify the error in this value receiver method

Which option correctly fixes the syntax error in this method? func (c Counter) Increment() { c.count++ } Assuming Counter is a struct with field count int.

A

func (c Counter) Increment() {
    c.count = c.count + 1
}

B

func (c *Counter) Increment() {
    c.count++
}

C

func Increment(c Counter) {
    c.count++
}

D

func (c Counter) Increment() {
    c.count += 1
}

💡 Hint

Which receiver type allows modifying the original struct?

Only option B uses a pointer receiver, allowing the method to modify the original struct's field.

🚀 Application

expert

Predict the output with mixed value and pointer receivers

What is the output of this program? package main import "fmt" type Number struct { n int } func (num Number) AddOne() { num.n++ } func (num *Number) AddTwo() { num.n += 2 } func main() { x := Number{n: 1} x.AddOne() fmt.Println(x.n) x.AddTwo() fmt.Println(x.n) }

A

1
1

B

2
3

C

1
3

D

2
4

💡 Hint

Remember which methods modify the original struct and which modify copies.

AddOne uses a value receiver, so it does not change x.n. AddTwo uses a pointer receiver, so it adds 2 to x.n.