Value receivers in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a method with a value receiver.

Go

type Counter struct {
    count int
}

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

Drag options to blanks, or click blank then click option'

A*

BCounter

Cc

D&

Attempts:

3 left

💡 Hint

Common Mistakes

Using * or & as the receiver variable name.

Using the type name instead of a variable name.

The method receiver must be a variable name, here c is the value receiver variable.

2fill in blank

medium

Complete the code to call the Increment method on a value receiver.

Go

c := Counter{count: 0}
c.[1]()
fmt.Println(c.count)

Drag options to blanks, or click blank then click option'

AincrementCount

BIncrement

CAdd

Dincrement

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase method names that do not exist.

Calling a method that is not defined.

The method name is Increment with uppercase I to export it.

3fill in blank

hard

Fix the error in the method receiver declaration.

Go

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

Drag options to blanks, or click blank then click option'

ACounter

B&c

C*c

Dc

Attempts:

3 left

💡 Hint

Common Mistakes

Using the type name as the receiver variable.

Using pointer dereference syntax in the receiver variable.

The receiver variable must be a name like c, not a type or pointer dereference.

4fill in blank

hard

Fill both blanks to define a method with a value receiver and print the count.

Go

func (c Counter) PrintCount() {
    fmt.Println(c.count)
}

Drag options to blanks, or click blank then click option'

Ac

BCounter

Ccount

D*Counter

Attempts:

3 left

💡 Hint

Common Mistakes

Using pointer type for value receiver.

Using wrong variable names.

The receiver variable is c and the type is Counter for a value receiver.

5fill in blank

hard

Fill all three blanks to create a value receiver method that increments count and prints it.

Go

func (c Counter) IncrementAndPrint() {
    c.count++
    fmt.Println(c.count)
}

Drag options to blanks, or click blank then click option'

Ac

BCounter

Ccount

D*Counter

Attempts:

3 left

💡 Hint

Common Mistakes

Using pointer type for value receiver.

Using wrong field name.

Using wrong variable name.

The receiver variable is c, the type is Counter, and the field accessed is count.

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