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.

Practice

1. What does a value receiver method in Go do when called on a struct?

easy

A. It requires a pointer to the struct to work.

B. It modifies the original struct directly.

C. It works on a copy of the struct, leaving the original unchanged.

D. It only works with built-in types, not structs.

Solution

1. Step 1: Understand value receiver behavior

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

2. Step 2: Compare with pointer receivers

   Pointer receivers work on the original struct, but value receivers do not.

3. Final Answer:

   It works on a copy of the struct, leaving the original unchanged. -> Option C

4. Quick Check:

   Value receiver = copy, no original change [OK]

Hint: Value receivers copy data; original stays safe [OK]

Common Mistakes:

• Thinking value receivers modify the original struct
• Confusing value and pointer receivers
• Assuming value receivers require pointers

2. Which of the following is the correct syntax to define a method with a value receiver in Go?

easy

A. func greet(p Person) {}

B. func (p Person) greet() {}

C. func (p *Person) greet() {}

D. func greet(*Person) {}

Solution

1. Step 1: Identify method receiver syntax

   Methods with receivers use the syntax: func (receiver Type) methodName() {}.

2. Step 2: Distinguish value vs pointer receiver

   Value receiver uses the type directly (e.g., Person), pointer receiver uses *Person.

3. Final Answer:

   func (p Person) greet() {} -> Option B

4. Quick Check:

   Value receiver syntax = func (p Type) method() [OK]

Hint: Value receiver uses type, pointer uses *type [OK]

Common Mistakes:

• Using pointer syntax for value receiver
• Defining method without receiver
• Confusing function parameter with method receiver

3. What will be the output of this Go program?

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)
}

medium

A. 5

B. 6

C. 0

D. Compilation error

Solution

1. Step 1: Analyze increment method with value receiver

   The increment method uses a value receiver, so it works on a copy of Counter, not the original.

2. Step 2: Check effect on original Counter

   Incrementing c.count inside the method changes only the copy; original c.count remains 5.

3. Final Answer:

   5 -> Option A

4. Quick Check:

   Value receiver method does not change original value [OK]

Hint: Value receiver methods don't change original struct [OK]

Common Mistakes:

• Assuming increment changes original count
• Confusing value and pointer receivers
• Expecting output 6 instead of 5

4. Identify the problem in this Go code snippet and fix it:

type Point struct { x, y int }
func (p Point) move(dx, dy int) {
    p.x += dx
    p.y += dy
}
func main() {
    pt := Point{1, 2}
    pt.move(3, 4)
    fmt.Println(pt)
}

medium

A. Use global variables instead of struct fields

B. Return new Point from move method

C. No fix needed; code works as intended

D. Change method receiver to pointer: func (p *Point) move(dx, dy int)

Solution

1. Step 1: Understand why move method doesn't update original

   Method uses value receiver, so changes affect only a copy, not original Point.

2. Step 2: Fix by using pointer receiver

   Changing receiver to *Point allows method to modify original struct fields.

3. Final Answer:

   Change method receiver to pointer: func (p *Point) move(dx, dy int) -> Option D

4. Quick Check:

   Pointer receiver needed to modify original struct [OK]

Hint: Use pointer receiver to modify struct fields [OK]

Common Mistakes:

• Not using pointer receiver for modifying methods
• Trying to fix by returning new struct without assignment
• Ignoring that value receiver copies struct

5. You have a struct Book with a method Display() using a value receiver. You want to add a method UpdateTitle(newTitle string) that changes the title. Which is the best approach?

hard

A. Define UpdateTitle with a pointer receiver to modify the original Book.

B. Define UpdateTitle with a value receiver and assign the new title inside it.

C. Keep both methods with value receivers for consistency.

D. Make Display use a pointer receiver instead of value receiver.

Solution

1. Step 1: Understand method receiver choice for updating data

   To change the original struct, methods must use pointer receivers.

2. Step 2: Decide best practice for mixed methods

   It's fine to have Display use value receiver (read-only), and UpdateTitle use pointer receiver (modifies data).

3. Final Answer:

   Define UpdateTitle with a pointer receiver to modify the original Book. -> Option A

4. Quick Check:

   Modify method uses pointer receiver; read-only can use value [OK]

Hint: Use pointer receiver for methods that change data [OK]

Common Mistakes:

• Using value receiver for methods that modify struct
• Changing all methods to pointer receivers unnecessarily
• Confusing method consistency with receiver type