Why methods are used in Go - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a method for the struct.

Go

func (p *Person) [1]() string {
    return p.name
}

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

APerson

Bname

Cfunc

DGetName

Attempts:

3 left

💡 Hint

Common Mistakes

Using the struct name instead of a method name.

Using 'func' as the method name.

The method name should be GetName to define a method that returns the name.

2fill in blank

medium

Complete the code to call the method on the struct instance.

Go

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

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

Aname

BPerson

CGetName

Dfunc

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to access the field directly instead of calling the method.

Using the struct name as a method call.

To call the method that returns the name, use GetName.

3fill in blank

hard

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

Go

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

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

A*

B&

Cvalue

Dref

Attempts:

3 left

💡 Hint

Common Mistakes

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

Using incorrect symbols like & or ref.

Using a pointer receiver *Person allows the method to modify the original struct.

4fill in blank

hard

Fill both blanks to create a method that returns the full name.

Go

func (p [1] Person) FullName() string {
    return p.firstName + [2] + p.lastName
}

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

A*

B+

C-

D&

Attempts:

3 left

💡 Hint

Common Mistakes

Using a value receiver that may copy the struct.

Using minus or ampersand instead of plus for string concatenation.

The pointer receiver *Person allows access to the struct, and + concatenates strings.

5fill in blank

hard

Fill all three blanks to define and call a method that updates and returns the age.

Go

func (p [1] Person) SetAge(newAge int) {
    p.age = newAge
}

func (p Person) GetAge() int {
    return p.[2]
}

p := Person{}
p.[3](30)
fmt.Println(p.GetAge())

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

A*

Bage

CSetAge

DGetAge

Attempts:

3 left

💡 Hint

Common Mistakes

Using value receiver in SetAge which does not update the original struct.

Returning wrong field name.

Calling the wrong method to set age.

Use a pointer receiver *Person in SetAge to modify the struct. The field age is returned by GetAge. Call SetAge to update the age.

Practice

1. Why do we use methods in Go programming language?

easy

A. To avoid using variables in the program

B. To write code that runs faster than functions

C. To associate functions with specific data types for better organization

D. To create global variables automatically

Solution

1. Step 1: Understand the purpose of methods

   Methods are functions tied to a specific data type, helping organize code logically.

2. Step 2: Compare methods with other options

   Options A, B, and D describe unrelated or incorrect uses of methods.

3. Final Answer:

   To associate functions with specific data types for better organization -> Option C

4. Quick Check:

   Methods connect actions to types = C [OK]

Hint: Methods link functions to types for clear code structure [OK]

Common Mistakes:

• Thinking methods make code run faster
• Confusing methods with variables
• Believing methods create global variables

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

easy

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

B. func UpdateName(p Person*, newName string) {}

C. func (p Person) *UpdateName(newName string) {}

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

Solution

1. Step 1: Recall Go method syntax with pointer receiver

   The receiver is declared inside parentheses before the method name, with *Type for pointer.

2. Step 2: Check each option

   func (p *Person) UpdateName(newName string) {} matches correct syntax: func (p *Person) MethodName(params) {}. Others have syntax errors.

3. Final Answer:

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

4. Quick Check:

   Pointer receiver syntax = D [OK]

Hint: Pointer receiver syntax: func (p *Type) method() {} [OK]

Common Mistakes:

• Placing * outside parentheses
• Using * in parameter list incorrectly
• Missing parentheses around receiver

3. What will be the output of the following Go code?

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. 6

B. 5

C. 0

D. Compilation error

Solution

1. Step 1: Understand pointer receiver effect

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

2. Step 2: Trace the code execution

   Initial value is 5, Increment adds 1, so value becomes 6, which is printed.

3. Final Answer:

   6 -> Option A

4. Quick Check:

   Pointer receiver changes value = 6 [OK]

Hint: Pointer receiver methods modify original data, so value changes [OK]

Common Mistakes:

• Thinking value stays 5 because method looks like a copy
• Assuming no output due to missing import
• Confusing pointer and value receivers

4. Identify the error in this Go method definition and fix it:

type Rectangle struct {
    width, height int
}

func (r Rectangle) Scale(factor int) {
    r.width = r.width * factor
    r.height = r.height * factor
}

medium

A. Change method name to lowercase: func (r Rectangle) scale(factor int) {}

B. Add return type: func (r Rectangle) Scale(factor int) Rectangle {}

C. Remove receiver: func Scale(factor int) {}

D. Change receiver to pointer: func (r *Rectangle) Scale(factor int) {}

Solution

1. Step 1: Understand why Scale does not change Rectangle

   The receiver is a value copy, so changes inside Scale do not affect original Rectangle.

2. Step 2: Fix by using pointer receiver

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

3. Final Answer:

   Change receiver to pointer: func (r *Rectangle) Scale(factor int) {} -> Option D

4. Quick Check:

   Pointer receiver needed to modify data = A [OK]

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

Common Mistakes:

• Using value receiver when modification is needed
• Adding return type unnecessarily
• Changing method name case without reason

5. You want to create a method that updates a user's email in a struct and also logs the change. Which approach best uses methods to achieve this in Go?

hard

A. Define a value receiver method that returns a new struct with updated email and logs externally

B. Define a pointer receiver method to update email and call a separate logging function inside it

C. Use a global function to update email and logging without methods

D. Define a method without receiver that updates email and logs

Solution

1. Step 1: Understand method purpose and data modification

   Updating email requires changing the original struct, so pointer receiver is needed.

2. Step 2: Combine update and logging logically

   Method with pointer receiver can update email and call logging function internally for reuse and clarity.

3. Final Answer:

   Define a pointer receiver method to update email and call a separate logging function inside it -> Option B

4. Quick Check:

   Pointer receiver + internal logging = A [OK]

Hint: Use pointer receiver method to update and log together [OK]

Common Mistakes:

• Using value receiver and expecting original to change
• Separating update and logging outside methods unnecessarily
• Avoiding methods and using only global functions