Receiver types in Go - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method with pointer 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 5

B 6

C 0

D Compilation error

💡 Hint

Think about how pointer receivers modify the original struct.

The method Increment has a pointer receiver, so it modifies the original Counter instance. Starting from 5, Increment adds 1, so the output is 6.

❓ Predict Output

intermediate

Value receiver method effect

What will be printed by this Go program?

Go

package main
import "fmt"
type Number struct {
    value int
}
func (n Number) Double() {
    n.value *= 2
}
func main() {
    num := Number{value: 10}
    num.Double()
    fmt.Println(num.value)
}

A Compilation error

B 20

C 0

D 10

💡 Hint

Consider if the method changes the original struct or a copy.

The Double method has a value receiver, so it works on a copy of num. The original num.value remains 10.

🔧 Debug

advanced

Why does this method not modify the struct?

Given this code, why does the method not change the struct's field?

Go

package main
import "fmt"
type Item struct {
    name string
}
func (i Item) Rename(newName string) {
    i.name = newName
}
func main() {
    it := Item{name: "Book"}
    it.Rename("Notebook")
    fmt.Println(it.name)
}

A Because Rename uses a value receiver, it modifies a copy, not the original struct.

B Because the field name is unexported and cannot be changed.

C Because the method Rename is not called properly.

D Because the struct Item is immutable in Go.

💡 Hint

Think about how value receivers work in Go methods.

Methods with value receivers get a copy of the struct. Changing fields on the copy does not affect the original struct.

❓ Predict Output

advanced

Output with mixed receiver types

What is the output of this Go program?

Go

package main
import "fmt"
type Box struct {
    size int
}
func (b Box) Grow() {
    b.size += 10
}
func (b *Box) Expand() {
    b.size += 20
}
func main() {
    b := Box{size: 5}
    b.Grow()
    b.Expand()
    fmt.Println(b.size)
}

A 25

B 35

C 15

D Compilation error

💡 Hint

Remember which methods modify the original struct and which do not.

Grow has a value receiver and does not change the original size (still 5). Expand has a pointer receiver and adds 20, so final size is 25.

🧠 Conceptual

expert

Choosing receiver types for methods

Which statement about receiver types in Go is correct?

A Value receivers always improve performance by avoiding pointers.

B Value receivers are required to modify the original struct fields.

C Pointer receivers allow methods to modify the original struct and avoid copying large structs.

D Pointer receivers cannot be used with interface types.

💡 Hint

Think about when you want to change the original data and efficiency.

Pointer receivers let methods change the original struct and avoid copying large structs. Value receivers work on copies and cannot modify the original.