Creating struct values in Go - Try It Yourself

Creating struct values

📖 Scenario: You are building a simple program to store information about a book in a library system.

🎯 Goal: Create a struct to represent a book and then create a value of that struct with specific details.

📋 What You'll Learn

Define a struct type named Book with fields Title (string), Author (string), and Year (int).

Create a variable named myBook of type Book with the exact values: Title = "The Go Programming Language", Author = "Alan A. A. Donovan", Year = 2015.

Print the myBook variable to display its contents.

💡 Why This Matters

🌍 Real World

Structs are used to group related data together, like storing information about books, users, or products in real applications.

💼 Career

Understanding structs is essential for Go programming jobs, as they are the foundation for creating complex data models.

1

Define the Book struct

Define a struct type called Book with three fields: Title of type string, Author of type string, and Year of type int.

Go

package main

type Book struct {
    // Define Title, Author, and Year fields here
}

func main() {

}

Hint

Use the type keyword to define a struct. Each field has a name and a type.

2

Create a Book value

Inside the main function, create a variable named myBook of type Book and assign it the values: Title = "The Go Programming Language", Author = "Alan A. A. Donovan", and Year = 2015.

Go

package main

type Book struct {
    Title  string
    Author string
    Year   int
}

func main() {
    // Create myBook variable with the given values
}

Hint

Use the struct literal syntax with field names to assign values.

3

Print the Book value

Add a fmt.Println statement inside main to print the myBook variable.

Go

package main

import "fmt"

type Book struct {
    Title  string
    Author string
    Year   int
}

func main() {
    myBook := Book{
        Title:  "The Go Programming Language",
        Author: "Alan A. A. Donovan",
        Year:   2015,
    }
    // Print myBook variable
}

Hint

Use fmt.Println to display the struct value.

4

Run and see the output

Run the program and observe the printed output showing the myBook struct with its field values.

Go

package main

import "fmt"

type Book struct {
    Title  string
    Author string
    Year   int
}

func main() {
    myBook := Book{
        Title:  "The Go Programming Language",
        Author: "Alan A. A. Donovan",
        Year:   2015,
    }
    fmt.Println(myBook) // Run and check output
}

Hint

The output should show the struct fields and their values inside curly braces.

Practice

1. What is the correct way to create a struct value with fields Name as "Alice" and Age as 30 in Go?

easy

A. person := Person("Alice", 30)

B. person := Person{30, "Alice"}

C. person := Person{Name: "Alice", Age: 30}

D. person := Person{Name = "Alice", Age = 30}

Solution

1. Step 1: Understand struct literal syntax

   In Go, struct values are created using the syntax StructType{FieldName: value, ...} for clarity and correctness.

2. Step 2: Match the syntax with the given options

   person := Person{Name: "Alice", Age: 30} uses the correct syntax with field names and values. Options A and C use positional values without field names, which is allowed but less clear and can cause errors if order changes. person := Person{Name = "Alice", Age = 30} uses '=' which is invalid in struct literals.

3. Final Answer:

   person := Person{Name: "Alice", Age: 30} -> Option C

4. Quick Check:

   Use field names with colons in struct literals = B [OK]

Hint: Use field names with colons to create structs clearly [OK]

Common Mistakes:

• Using parentheses instead of braces
• Using '=' instead of ':' in struct literals
• Mixing field order without names causing confusion

2. Which of the following is the correct syntax to create a struct value with zero values for all fields in Go?

easy

A. p := Person{}

B. p := Person()

C. p := new(Person)

D. p := Person(nil)

Solution

1. Step 1: Recall zero value struct creation

   In Go, creating a struct with zero values for all fields is done by using empty braces after the struct type: StructType{}.

2. Step 2: Evaluate options

   p := Person{} uses Person{} which creates a struct with zero values. p := Person() uses parentheses which is invalid syntax. p := new(Person) uses new(Person) which returns a pointer, not a struct value. p := Person(nil) uses nil which is invalid for struct values.

3. Final Answer:

   p := Person{} -> Option A

4. Quick Check:

   Empty braces create zero-value struct = C [OK]

Hint: Use empty braces {} to create zero-value struct [OK]

Common Mistakes:

• Using parentheses instead of braces
• Confusing new() pointer with struct value
• Passing nil to struct literal

3. Given the struct and code below, what will be printed?

type Person struct {
    Name string
    Age  int
}

func main() {
    p := Person{Name: "Bob", Age: 25}
    p.Age = 26
    fmt.Println(p)
}

medium

A. {Bob 25}

B. {Bob 26}

C. Person{Name: "Bob", Age: 26}

D. Syntax error

Solution

1. Step 1: Create struct and modify field

   The struct Person is created with Name "Bob" and Age 25. Then the Age field is updated to 26.

2. Step 2: Print the struct value

   Printing the struct with fmt.Println shows the field values in braces. Since Age was updated to 26, the output is {Bob 26}.

3. Final Answer:

   {Bob 26} -> Option B

4. Quick Check:

   Updated field value shows in output = D [OK]

Hint: Changing a field after creation updates printed struct [OK]

Common Mistakes:

• Assuming original Age remains unchanged
• Expecting struct type name in print output
• Confusing syntax error with valid code

4. What is wrong with the following code snippet?

type Person struct {
    Name string
    Age  int
}

func main() {
    p := Person{Name: "Eve", Age: "30"}
    fmt.Println(p)
}

medium

A. Age field has wrong type value

B. Missing parentheses in struct creation

C. Name field is not initialized

D. fmt.Println cannot print structs

Solution

1. Step 1: Check field types in struct literal

   The struct Person has Age as int type, but the code assigns "30" which is a string, causing a type mismatch error.

2. Step 2: Identify the error cause

   Assigning a string to an int field is invalid in Go and causes a compile-time error.

3. Final Answer:

   Age field has wrong type value -> Option A

4. Quick Check:

   Field types must match exactly = A [OK]

Hint: Match field types exactly when creating struct values [OK]

Common Mistakes:

• Assigning string to int field
• Confusing struct literal syntax errors
• Thinking fmt.Println can't print structs

5. How can you create a slice of struct values representing three people with names "Anna", "Ben", "Cara" and ages 22, 28, 31 respectively in Go?

hard

A. people := []Person{Person("Anna", 22), Person("Ben", 28), Person("Cara", 31)}

B. people := [Person]{Name: "Anna", Age: 22, Name: "Ben", Age: 28, Name: "Cara", Age: 31}

C. people := []Person{Name: "Anna", Age: 22, Name: "Ben", Age: 28, Name: "Cara", Age: 31}

D. people := []Person{{Name: "Anna", Age: 22}, {Name: "Ben", Age: 28}, {Name: "Cara", Age: 31}}

Solution

1. Step 1: Understand slice of structs syntax

   A slice of structs is created using []StructType{...} with each element as a struct literal.

2. Step 2: Check each option for correct syntax

   people := []Person{{Name: "Anna", Age: 22}, {Name: "Ben", Age: 28}, {Name: "Cara", Age: 31}} correctly creates a slice with three struct literals using field names. people := [Person]{Name: "Anna", Age: 22, Name: "Ben", Age: 28, Name: "Cara", Age: 31} uses array syntax but incorrect literal format. people := []Person{Name: "Anna", Age: 22, Name: "Ben", Age: 28, Name: "Cara", Age: 31} tries to create slice but misses braces for each struct. people := []Person{Person("Anna", 22), Person("Ben", 28), Person("Cara", 31)} uses parentheses which is invalid for struct literals.

3. Final Answer:

   people := []Person{{Name: "Anna", Age: 22}, {Name: "Ben", Age: 28}, {Name: "Cara", Age: 31}} -> Option D

4. Quick Check:

   Slice of structs uses []Type{{...}, {...}} = A [OK]

Hint: Use double braces for slice of struct literals [OK]

Common Mistakes:

• Using parentheses instead of braces for structs
• Missing braces around each struct in slice
• Confusing array and slice syntax