Receiver types in Go - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

Go

func (p [1]) Greet() string {
    return "Hello, " + p.name
}

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

Aperson

BPerson

C*Person

D&Person

Attempts:

3 left

💡 Hint

Common Mistakes

Using a value receiver when a pointer receiver is needed.

Forgetting the asterisk (*) in the receiver type.

The method receiver must be a pointer type *Person to modify the original struct.

2fill in blank

medium

Complete the code to call the method with a pointer receiver correctly.

Go

p := Person{name: "Alice"}
result := p.[1]()

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

AGreet()

B&Greet

C*Greet

DGreet

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call the method with & or * symbols.

Adding parentheses in the method name inside the call.

Go automatically handles calling pointer receiver methods on value variables, so just use p.Greet().

3fill in blank

hard

Fix the error in the method receiver declaration.

Go

func ([1] Person) UpdateName(newName string) {
    p.name = newName
}

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

Ap

B*p

CPerson

D*Person

Attempts:

3 left

💡 Hint

Common Mistakes

Using the type name instead of a variable name as receiver.

Using pointer syntax incorrectly in the receiver variable name.

The receiver variable name should be an identifier like p, not a type.

4fill in blank

hard

Fill both blanks to define a method with a pointer receiver and update the struct field.

Go

func ([1] [2]) UpdateAge(newAge int) {
    p.age = newAge
}

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

Ap

BPerson

C*Person

Dage

Attempts:

3 left

💡 Hint

Common Mistakes

Using a value receiver when a pointer receiver is needed to modify fields.

Using the struct name as the receiver variable.

The receiver variable is p and the receiver type is a pointer *Person to modify the original struct.

5fill in blank

hard

Fill all three blanks to create a method with a value receiver that returns the person's name in uppercase.

Go

func ([1] [2]) NameUpper() string {
    return strings.[3](p.name)
}

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

Ap

BPerson

CToUpper

DToLower

Attempts:

3 left

💡 Hint

Common Mistakes

Using pointer receiver when value receiver is intended.

Using ToLower instead of ToUpper.

Incorrect receiver variable name.

The receiver variable is p, the receiver type is Person (value receiver), and the function to convert to uppercase is ToUpper from the strings package.

Practice

1. What is the main difference between a value receiver and a pointer receiver in Go methods?

easy

A. Value receivers are faster than pointer receivers in all cases.

B. Value receivers can only read data; pointer receivers can only write data.

C. Pointer receivers create a new copy of the data each time.

D. Value receivers get a copy of the data; pointer receivers get the original data to modify.

Solution

1. Step 1: Understand receiver types

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

2. Step 2: Pointer receivers behavior

   Pointer receivers receive the address of the original data, allowing methods to modify the original value.

3. Final Answer:

   Value receivers get a copy of the data; pointer receivers get the original data to modify. -> Option D

4. Quick Check:

   Receiver type = copy vs original [OK]

Hint: Pointer receivers allow modifying original data, value receivers do not [OK]

Common Mistakes:

• Thinking value receivers modify original data
• Believing pointer receivers create copies
• Assuming pointer receivers are always slower

2. Which of the following is the correct syntax to define a method with a pointer receiver for a struct Person?

easy

A. func (p Person) Greet() string { return "Hi" }

B. func (p *Person) Greet() string { return "Hi" }

C. func Greet(p *Person) string { return "Hi" }

D. func (p Person*) Greet() string { return "Hi" }

Solution

1. Step 1: Identify pointer receiver syntax

   Pointer receivers use an asterisk before the type in the receiver: (p *Person).

2. Step 2: Check method declaration format

   The method must be declared with receiver in parentheses before the method name.

3. Final Answer:

   func (p *Person) Greet() string { return "Hi" } -> Option B

4. Quick Check:

   Pointer receiver syntax = (p *Type) [OK]

Hint: Pointer receiver syntax uses * before type inside parentheses [OK]

Common Mistakes:

• Missing parentheses around receiver
• Placing * after variable name instead of type
• Defining method without 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 (c *Counter) IncrementPtr() { c.count++ }
func main() {
  c := Counter{count: 5}
  c.Increment()
  fmt.Println(c.count)
  c.IncrementPtr()
  fmt.Println(c.count)
}

medium

A. 5
6

B. 5
5

C. 6
6

D. 6
7

Solution

1. Step 1: Analyze Increment method with value receiver

   Increment uses a value receiver, so it works on a copy. The original count remains 5 after calling Increment.

2. Step 2: Analyze IncrementPtr method with pointer receiver

   IncrementPtr uses a pointer receiver, so it modifies the original count from 5 to 6.

3. Final Answer:

   5 6 -> Option A

4. Quick Check:

   Value receiver no change, pointer receiver changes [OK]

Hint: Value receiver copies data; pointer receiver changes original [OK]

Common Mistakes:

• Assuming value receiver changes original
• Confusing method calls with pointer vs value receivers
• Expecting both increments to change count

4. Identify the error in this Go code snippet:

type Rectangle struct { width, height int }
func (r Rectangle) Scale(factor int) {
  r.width = r.width * factor
  r.height = r.height * factor
}
func main() {
  rect := Rectangle{2, 3}
  rect.Scale(2)
  fmt.Println(rect.width, rect.height)
}

medium

A. The struct fields width and height must be pointers.

B. Scale method must return a new Rectangle instead of modifying fields.

C. Scale method should have a pointer receiver to modify Rectangle fields.

D. The Scale method should be defined outside the Rectangle type.

Solution

1. Step 1: Check receiver type in Scale method

   Scale uses a value receiver, so it works on a copy and does not modify the original Rectangle.

2. Step 2: Fix receiver to pointer to modify original

   Changing receiver to pointer (r *Rectangle) allows Scale to modify the original struct fields.

3. Final Answer:

   Scale method should have a pointer receiver to modify Rectangle fields. -> Option C

4. Quick Check:

   Modify struct fields = pointer receiver needed [OK]

Hint: Use pointer receiver to change struct fields inside methods [OK]

Common Mistakes:

• Using value receiver expecting changes to persist
• Trying to make struct fields pointers unnecessarily
• Thinking methods must be outside struct

5. You want to create a Go method Reset for a struct Timer that sets its seconds field to zero. Which receiver type should you use and why?

hard

A. Use a pointer receiver because you need to modify the original Timer's seconds field.

B. Use a value receiver because it is simpler and does not modify the original.

C. Use a value receiver and return a new Timer with seconds zeroed.

D. Use a pointer receiver but do not modify any fields inside the method.

Solution

1. Step 1: Understand the goal of Reset method

   Reset must change the Timer's seconds field to zero, modifying the original struct.

2. Step 2: Choose receiver type to allow modification

   Pointer receiver is needed to modify the original Timer instance inside the method.

3. Final Answer:

   Use a pointer receiver because you need to modify the original Timer's seconds field. -> Option A

4. Quick Check:

   Modify original struct = pointer receiver [OK]

Hint: Modify original struct? Use pointer receiver [OK]

Common Mistakes:

• Using value receiver expecting original to change
• Returning new struct instead of modifying original
• Using pointer receiver but not modifying fields