Pointer receivers 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] Person) SetName(name string) {
    p.Name = 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 (Person) which does not modify the original struct.

The method receiver must be a pointer to modify the original struct. Using *Person allows changes to affect the original instance.

2fill in blank

medium

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

Go

p := Person{Name: "Alice"}
p.[1]("Bob")

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

Asetname

BSetName

CsetName

DSetname

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect capitalization for the method name.

Method names in Go are case-sensitive and usually start with a capital letter if exported. The method defined is SetName.

3fill in blank

hard

Fix the error in the method receiver declaration to allow modifying the struct.

Go

func (p [1] Person) UpdateAge(age int) {
    p.Age = age
}

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

A*Person

BPerson

C&Person

Dperson

Attempts:

3 left

💡 Hint

Common Mistakes

Using a value receiver which does not update the original struct.

To modify the original struct, the receiver must be a pointer type *Person. Using a value receiver copies the struct and changes won't persist.

4fill in blank

hard

Fill both blanks to create a pointer receiver method that increments Age by 1.

Go

func (p [1] Person) [2]() {
    p.Age++
}

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

A*Person

BPerson

CIncrementAge

DincrementAge

Attempts:

3 left

💡 Hint

Common Mistakes

Using a value receiver which does not modify the original struct.

Using lowercase method name which may not be exported.

The receiver must be a pointer *Person to modify the original struct. The method name IncrementAge follows Go naming conventions with capital letter.

5fill in blank

hard

Fill all three blanks to define a pointer receiver method that resets Name and Age.

Go

func (p [1] Person) [2]() {
    p.Name = [3]
    p.Age = 0
}

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

A*Person

BReset

C""

DPerson

Attempts:

3 left

💡 Hint

Common Mistakes

Using a value receiver which does not update the original struct.

Forgetting to reset Name to an empty string.

The receiver must be a pointer *Person to modify the original struct. The method name Reset is capitalized. The empty string "" resets the Name field.

Practice

1. What is the main benefit of using a pointer receiver in Go methods?

easy

A. It allows the method to modify the original struct data.

B. It makes the method run faster by using multiple CPU cores.

C. It automatically creates a copy of the struct for safety.

D. It prevents the method from accessing struct fields.

Solution

1. Step 1: Understand pointer receiver purpose

   Pointer receivers let methods access and change the original struct, not a copy.

2. Step 2: Compare with value receivers

   Value receivers get a copy, so changes inside the method don't affect the original struct.

3. Final Answer:

   It allows the method to modify the original struct data. -> Option A

4. Quick Check:

   Pointer receiver modifies original struct = A [OK]

Hint: Pointer receivers let methods change original data directly [OK]

Common Mistakes:

• Thinking pointer receivers run methods on copies
• Confusing pointer receivers with concurrency
• Believing pointer receivers prevent access to fields

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

easy

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

B. func (p Person) UpdateName(name string) {}

C. func UpdateName(p Person, name string) {}

D. func UpdateName(*Person p, name string) {}

Solution

1. Step 1: Identify pointer receiver syntax

   Pointer receiver syntax uses (p *Person) before method name.

2. Step 2: Check each option

   func (p *Person) UpdateName(name string) {} correctly uses func (p *Person) UpdateName(name string) {}. Others either use value receiver or wrong syntax.

3. Final Answer:

   func (p *Person) UpdateName(name string) {} -> Option A

4. Quick Check:

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

Hint: Pointer receiver always uses * before struct name in method receiver [OK]

Common Mistakes:

• Using value receiver syntax instead of pointer
• Placing * incorrectly in function parameters
• Confusing method receiver with function parameters

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

package main
import "fmt"
type Counter struct { value int }
func (c *Counter) Increment() { c.value++ }
func main() {
 c := Counter{value: 5}
 c.Increment()
 fmt.Println(c.value)
}

medium

A. 5

B. Compilation error

C. 0

D. 6

Solution

1. Step 1: Understand method call with pointer receiver

   The method Increment has a pointer receiver, so it modifies the original Counter struct's value.

2. Step 2: Trace the code execution

   Initial value is 5, calling Increment() increases it by 1, so value becomes 6. Then it prints 6.

3. Final Answer:

   6 -> Option D

4. Quick Check:

   Pointer receiver increments original value = 6 [OK]

Hint: Pointer receiver methods change original struct values [OK]

Common Mistakes:

• Assuming value receiver copies and does not change original
• Expecting output 5 without increment
• Thinking code causes compile error

4. Identify the error in this Go code snippet:

package main
import "fmt"
type Item struct { count int }
func (i Item) Increase() { i.count++ }
func main() {
 item := Item{count: 10}
 item.Increase()
 fmt.Println(item.count)
}

medium

A. Struct Item is missing a field tag.

B. fmt.Println cannot print struct fields directly.

C. Method Increase should have a pointer receiver to modify count.

D. Increase method must return the new count.

Solution

1. Step 1: Analyze method receiver type

   The method Increase uses a value receiver, so it works on a copy of Item.

2. Step 2: Understand effect on original struct

   Since it modifies the copy, the original item.count remains unchanged at 10.

3. Final Answer:

   Method Increase should have a pointer receiver to modify count. -> Option C

4. Quick Check:

   Value receiver does not change original struct = B [OK]

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

Common Mistakes:

• Thinking value receiver modifies original struct
• Believing fmt.Println can't print fields
• Expecting method must return value to update

5. You want to create a method Reset for struct Timer that sets its seconds field to zero. Which approach correctly uses pointer receivers to ensure the original Timer is reset?

type Timer struct { seconds int }
// Choose the correct Reset method:

hard

A. func (t Timer) Reset() { t.seconds = 0 }

B. func (t *Timer) Reset() { t.seconds = 0 }

C. func Reset(t Timer) { t.seconds = 0 }

D. func Reset(t *Timer) int { t.seconds = 0; return t.seconds }

Solution

1. Step 1: Understand method receiver for modifying struct

   To modify the original Timer, the method must have a pointer receiver (t *Timer).

2. Step 2: Check each option's effect

   The pointer receiver func (t *Timer) Reset() { t.seconds = 0 } correctly modifies the original struct. The value receiver version works on a copy, so changes won't persist. The plain function signatures are not methods attached to the Timer type, and returning a value is unnecessary for a reset operation.

3. Final Answer:

   func (t *Timer) Reset() { t.seconds = 0 } -> Option B

4. Quick Check:

   Pointer receiver method resets original struct = C [OK]

Hint: Reset original struct fields with pointer receiver methods [OK]

Common Mistakes:

• Using value receiver and expecting original change
• Confusing functions with methods
• Returning value unnecessarily in reset method