Accessing struct fields in Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a struct in Go?

A struct in Go is a collection of fields grouped together to form a single data type. It is used to represent a record or an object with multiple properties.

beginner

How do you access a field named Name in a struct variable person?

You access it using the dot notation: person.Name. This retrieves the value stored in the Name field of the person struct.

intermediate

Given a pointer to a struct p *Person, how do you access the Age field?

You can access it using p.Age. Go automatically dereferences the pointer when accessing fields, so you don't need to write (*p).Age.

beginner

What happens if you try to access a field that does not exist in a struct?

The Go compiler will give an error saying the field does not exist. You must only access fields defined in the struct type.

beginner

Why is using structs useful in Go programming?

Structs let you group related data together, making your code organized and easier to understand. They help model real-world objects with multiple properties.

How do you access the field Title of a struct variable book?

A book:Title

B book.Title

C book[Title]

D book->Title

In Go, struct fields are accessed using dot notation like book.Title.

If p is a pointer to a struct, which is correct to access field Age?

A p->Age

B *p.Age

C p.Age

D p[Age]

Go automatically dereferences pointers when accessing struct fields, so p.Age works.

What error occurs if you try to access a non-existent field in a struct?

A Compile-time error

B Runtime panic

C Silent failure

D Returns zero value

The Go compiler reports an error if you try to access a field not defined in the struct.

Which of these is a valid way to define a struct in Go?

A struct Person { Name string; Age int }

B class Person { Name string; Age int }

C Person = struct(Name string, Age int)

D type Person struct { Name string; Age int }

In Go, structs are defined using the syntax: type Name struct { fields }.

Why use structs in Go?

A To group related data together

B To perform arithmetic operations

C To create loops

D To handle errors

Structs group related data fields into one unit, modeling real-world objects.

Explain how to access fields in a Go struct and how pointers to structs affect this access.

Think about how you write <code>person.Name</code> and how Go lets you use <code>p.Age</code> if p is a pointer.

Describe what happens if you try to access a field that does not exist in a Go struct.

Remember Go checks field names when you compile your program.

Practice

1.

Which of the following is the correct way to access the Age field of a struct variable person in Go?

easy

A. person.Age()

B. person->Age

C. person["Age"]

D. person.Age

Solution

1. Step 1: Understand struct field access syntax in Go

   In Go, struct fields are accessed using dot notation: structVariable.fieldName.

2. Step 2: Apply to the given variable and field

   For variable person and field Age, the correct access is person.Age.

3. Final Answer:

   person.Age -> Option D

4. Quick Check:

   Use dot notation for struct fields = person.Age [OK]

Hint: Use dot (.) to access struct fields in Go [OK]

Common Mistakes:

• Using arrow (->) like in C/C++
• Trying to access fields like map keys
• Calling field as a function with ()

2.

Which of the following code snippets correctly accesses the Title field of a struct book?

type Book struct {
    Title string
    Author string
}

var book Book
// Access Title here

easy

A. book.Title

B. book->Title

C. book["Title"]

D. book.Title()

Solution

1. Step 1: Recall Go struct field access syntax

   Fields in Go structs are accessed using dot notation without parentheses or brackets.

2. Step 2: Apply to the book variable and Title field

   The correct syntax is book.Title.

3. Final Answer:

   book.Title -> Option A

4. Quick Check:

   Dot notation accesses struct fields = book.Title [OK]

Hint: Remember: struct fields use dot, not brackets or arrows [OK]

Common Mistakes:

• Using brackets like a map
• Using arrow operator (->)
• Calling field as a method

3.

What will be the output of the following Go program?

package main
import "fmt"

type Person struct {
    Name string
    Age  int
}

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

medium

A. Alice

B. 30

C. Name

D. Compilation error

Solution

1. Step 1: Understand struct initialization and field access

   The struct Person is initialized with Name: "Alice" and Age: 30. The variable p holds this struct.

2. Step 2: Identify the printed field

   The code prints p.Age, which is 30.

3. Final Answer:

   30 -> Option B

4. Quick Check:

   Print struct field Age = 30 [OK]

Hint: Print struct.field to get that field's value [OK]

Common Mistakes:

• Printing the Name field instead of Age
• Expecting field name as output
• Thinking code causes error

4.

Identify the error in the following Go code and choose the correct fix:

package main
import "fmt"

type Car struct {
    Model string
    Year  int
}

func main() {
    c := Car{Model: "Tesla", Year: 2022}
    fmt.Println(c->Model)
}

medium

A. Add parentheses: c.Model()

B. Change c->Model to c["Model"]

C. Change c->Model to c.Model

D. No error, code is correct

Solution

1. Step 1: Identify incorrect field access operator

   The code uses c->Model, which is invalid in Go. Go uses dot notation for struct fields.

2. Step 2: Correct the field access syntax

   Replace c->Model with c.Model to fix the error.

3. Final Answer:

   Change c->Model to c.Model -> Option C

4. Quick Check:

   Use dot (.) not arrow (->) for struct fields [OK]

Hint: Use dot (.) for struct fields, not arrow (->) [OK]

Common Mistakes:

• Using arrow operator like in C/C++
• Trying to access fields like map keys
• Calling field as a function

5.

Given the struct and code below, what will be the output?

package main
import "fmt"

type Employee struct {
    ID    int
    Name  string
    Title string
}

func main() {
    e := Employee{ID: 101, Name: "Bob", Title: "Developer"}
    e.Title = "Senior Developer"
    fmt.Println(e.Title)
}

hard

A. Senior Developer

B. Developer

C. Title

D. Compilation error

Solution

1. Step 1: Understand struct field update

   The struct Employee is created with Title: "Developer". Then the field Title is updated to "Senior Developer".

2. Step 2: Identify printed value

   The code prints e.Title after update, so output is Senior Developer.

3. Final Answer:

   Senior Developer -> Option A

4. Quick Check:

   Updated struct field prints new value [OK]

Hint: Assign new value with dot, then print updated field [OK]

Common Mistakes:

• Expecting original value instead of updated
• Thinking field cannot be changed
• Confusing field name with value