Nested structs in Go - Mini Project: Build & Apply

Nested structs

📖 Scenario: You are creating a simple program to store information about a book and its author. The author has a name and an age. The book has a title and an author.

🎯 Goal: You will build a Go program that uses nested structs to represent a book and its author, then print the book's title and the author's name.

📋 What You'll Learn

Create a struct called Author with fields Name string and Age int.

Create a struct called Book with fields Title string and Author Author.

Create a variable myBook of type Book with title "Go Programming" and author name "Alice" aged 30.

Print the book's title and the author's name exactly as shown.

💡 Why This Matters

🌍 Real World

Nested structs are useful to model real-world objects that have parts or details inside them, like a book having an author.

💼 Career

Understanding nested structs is important for Go developers working on data modeling, APIs, and complex data structures.

1

Define the Author struct

Write a struct called Author with two fields: Name of type string and Age of type int.

Go

package main

// Define the Author struct here

type Author struct {
    // Your code here
}

func main() {

}

Hint

Use type Author struct {} and add the fields inside the braces.

2

Define the Book struct with nested Author

Write a struct called Book with two fields: Title of type string and Author of type Author (the struct you defined earlier).

Go

package main

type Author struct {
    Name string
    Age  int
}

// Define the Book struct here

type Book struct {
    // Your code here
}

func main() {

}

Hint

Use type Book struct { Title string; Author Author } to nest the Author struct inside Book.

3

Create a variable myBook with nested data

Inside main(), create a variable called myBook of type Book. Set its Title to "Go Programming" and its Author to an Author struct with Name "Alice" and Age 30.

Go

package main

type Author struct {
    Name string
    Age  int
}

type Book struct {
    Title  string
    Author Author
}

func main() {
    // Create myBook variable here
    // Your code here
}

Hint

Use composite literals to set nested struct fields, like myBook := Book{ Title: "Go Programming", Author: Author{Name: "Alice", Age: 30} }.

4

Print the book title and author name

Add a fmt.Println statement inside main() to print the book's title and the author's name in this exact format: "Title: Go Programming, Author: Alice". Remember to import the fmt package.

Go

package main

import "fmt"

type Author struct {
    Name string
    Age  int
}

type Book struct {
    Title  string
    Author Author
}

func main() {
    myBook := Book{
        Title: "Go Programming",
        Author: Author{
            Name: "Alice",
            Age:  30,
        },
    }
    // Print the book title and author name
    // Your code here
}

Hint

Use fmt.Println("Title: ", myBook.Title, ", Author: ", myBook.Author.Name) to print the values.

Practice

1. What is the main purpose of using nested structs in Go?

easy

A. To group related data together inside another struct

B. To create multiple independent structs

C. To make the program run faster

D. To avoid using functions

Solution

1. Step 1: Understand struct grouping

   Nested structs allow one struct to contain another, grouping related data logically.

2. Step 2: Compare options

   Creating multiple independent structs, making the program run faster, or avoiding functions do not describe grouping data inside structs.

3. Final Answer:

   To group related data together inside another struct -> Option A

4. Quick Check:

   Nested structs = Group related data [OK]

Hint: Think of nested structs as folders inside folders [OK]

Common Mistakes:

• Confusing nested structs with separate structs
• Thinking nested structs improve speed
• Believing nested structs replace functions

2. Which of the following is the correct way to access the field City inside a nested struct Address within struct Person?

easy

A. person.City.Address

B. person->Address->City

C. person.Address.City

D. person.Address->City

Solution

1. Step 1: Recall Go syntax for nested structs

   Access nested fields using dot notation: Outer.Inner.Field.

2. Step 2: Evaluate options

   person.Address.City uses correct dot notation. Arrow syntax (->) is invalid in Go. person.City.Address reverses the order.

3. Final Answer:

   person.Address.City -> Option C

4. Quick Check:

   Dot notation = person.Address.City [OK]

Hint: Use dot notation to access nested fields [OK]

Common Mistakes:

• Using arrow (->) instead of dot (.)
• Reversing the order of fields
• Trying to access nested fields directly without parent

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

package main
import "fmt"
type Address struct {
    City string
    Zip  int
}
type Person struct {
    Name    string
    Address Address
}
func main() {
    p := Person{Name: "Anna", Address: Address{City: "Paris", Zip: 75000}}
    fmt.Println(p.Address.City)
}

medium

A. Anna

B. Paris

C. 75000

D. Address

Solution

1. Step 1: Understand struct initialization

   Person struct has Name and Address fields. Address is initialized with City "Paris" and Zip 75000.

2. Step 2: Identify printed field

   The code prints p.Address.City, which is "Paris".

3. Final Answer:

   Paris -> Option B

4. Quick Check:

   p.Address.City = Paris [OK]

Hint: Print nested field with dot notation [OK]

Common Mistakes:

• Printing the wrong field like Name or Zip
• Confusing struct field names
• Expecting the whole struct to print

4. Identify the error in this Go code snippet involving nested structs:

package main
import "fmt"
type Engine struct {
    Power int
}
type Car struct {
    Model  string
    Engine Engine
}
func main() {
    c := Car{Model: "Sedan"}
    fmt.Println(c.Engine.Power)
}

medium

A. c.Engine.Power is zero value, no error

B. Car struct missing Engine field

C. Engine struct is not defined

D. Cannot print nested struct fields directly

Solution

1. Step 1: Check struct definitions

   Engine and Car structs are defined correctly. Car has Engine field.

2. Step 2: Analyze initialization and print

   Car instance c is created with Model only. Engine field is zero-valued (Power = 0). Printing c.Engine.Power prints 0 without error.

3. Final Answer:

   c.Engine.Power is zero value, no error -> Option A

4. Quick Check:

   Uninitialized nested struct fields have zero values [OK]

Hint: Uninitialized nested structs have zero values [OK]

Common Mistakes:

• Assuming missing initialization causes error
• Thinking nested fields can't be printed
• Confusing missing fields with zero values

5. Given the structs below, how would you write a function FullAddress that returns a formatted string combining Street, City, and Zip from nested structs?

type Location struct {
    Street string
    City   string
}
type Address struct {
    Location Location
    Zip      int
}

hard

A. func FullAddress(a Address) string { return a.Street + ", " + a.City + " " + fmt.Sprint(a.Zip) }

B. func FullAddress(a Address) string { return a.Street + ", " + a.Location.City + " " + fmt.Sprint(a.Zip) }

C. func FullAddress(a Address) string { return a.Location.Street + ", " + a.City + " " + fmt.Sprint(a.Zip) }

D. func FullAddress(a Address) string { return a.Location.Street + ", " + a.Location.City + " " + fmt.Sprint(a.Zip) }

Solution

1. Step 1: Identify nested fields

   Street and City are inside Location struct, which is nested inside Address.

2. Step 2: Access nested fields correctly

   Use a.Location.Street and a.Location.City to access those fields, and a.Zip for Zip code.

3. Step 3: Check options

   Only func FullAddress(a Address) string { return a.Location.Street + ", " + a.Location.City + " " + fmt.Sprint(a.Zip) } correctly accesses nested fields with dot notation.

4. Final Answer:

   func FullAddress(a Address) string { return a.Location.Street + ", " + a.Location.City + " " + fmt.Sprint(a.Zip) } -> Option D

5. Quick Check:

   Access nested fields with dot notation [OK]

Hint: Use dot notation for each nested level [OK]

Common Mistakes:

• Accessing nested fields directly without parent struct
• Mixing field names from different structs
• Forgetting to convert int Zip to string