Pointer receivers 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 6

B Compilation error

C 0

D 5

💡 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

Effect of value receiver on struct modification

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 0

B 20

C 10

D Compilation error

💡 Hint

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

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

🔧 Debug

advanced

Why does this pointer receiver method not update the struct?

This Go code intends to update the field of a struct using a pointer receiver method, but it does not work as expected. What is the reason?

Go

package main
import "fmt"
type Item struct {
    name string
}
func (i *Item) Rename(newName string) {
    i = &Item{name: newName}
}
func main() {
    it := Item{name: "Old"}
    it.Rename("New")
    fmt.Println(it.name)
}

A The method should have a value receiver instead of a pointer receiver.

B The method Rename is missing a return statement.

C The struct field name is unexported and cannot be modified.

D The method assigns a new pointer to i, but does not modify the original struct's fields.

💡 Hint

Think about what happens when you assign to the pointer receiver variable inside the method.

Assigning a new pointer to i inside Rename only changes the local copy of the pointer. It does not affect the original struct. To update the struct, modify its fields directly.

📝 Syntax

advanced

Identify the syntax error in pointer receiver method

Which option contains a syntax error in defining a pointer receiver method in Go?

A func (p Person*) SetName(name string) { p.name = name }

B } eman = eman.p { )gnirts eman(emaNteS )nosreP* p( cnuf

C unc (p *Person) SetName(name string) { p.name = name }

D func (p *Person) SetName(name string) { p.name = name }

💡 Hint

Check the placement of the asterisk in the receiver syntax.

In Go, the pointer receiver syntax is (p *Type), not (p Type*). Option A has the asterisk after the type, which is invalid syntax.

🚀 Application

expert

Determine the final value after method calls with mixed receivers

Given the following Go code, what is the final value printed?

Go

package main
import "fmt"
type Counter struct {
    value int
}
func (c Counter) Add(n int) {
    c.value += n
}
func (c *Counter) AddPtr(n int) {
    c.value += n
}
func main() {
    c := Counter{value: 1}
    c.Add(2)
    c.AddPtr(3)
    fmt.Println(c.value)
}

A 6

B 4

C 3

D 1

💡 Hint

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

Add uses a value receiver, so it works on a copy and does not change c.value. AddPtr uses a pointer receiver and adds 3 to the original c.value (1 + 3 = 4). So final value is 4.