Accessing struct fields in Go - Step-by-Step Execution

Concept Flow - Accessing struct fields

Define struct type

↓

Create struct variable

↓

Access field using dot

↓

Use or print field value

↓

END

First, we define a struct type, then create a variable of that type. We access fields using the dot (.) operator and use the values.

Execution Sample

Go

package main

import "fmt"

type Person struct {
    Name string
    Age  int
}

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

This code defines a Person struct, creates a variable p, and prints the Name field.

Execution Table

Step	Action	Variable/Field	Value	Output
1	Define struct type Person	Person	struct with fields Name(string), Age(int)
2	Create variable p	p	Person{Name: "Alice", Age: 30}
3	Access field p.Name	p.Name	"Alice"
4	Print p.Name			Alice
5	End of program

💡 Program ends after printing the Name field value.

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
p	undefined	Person{Name: "Alice", Age: 30}	Person{Name: "Alice", Age: 30}	Person{Name: "Alice", Age: 30}
p.Name	undefined	"Alice"	"Alice"	"Alice"
p.Age	undefined	30	30	30

Key Moments - 2 Insights

Why do we use a dot (.) to access struct fields?

The dot operator connects the struct variable to its fields. For example, p.Name accesses the Name field inside p. See execution_table step 3.

Can we access a field before creating the struct variable?

No, the struct variable must exist first. In the table, p is created at step 2 before accessing p.Name at step 3.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of p.Name at step 3?

A "30"

B undefined

C "Alice"

D Person struct

💡 Hint

Check the 'Value' column at step 3 in the execution_table.

At which step is the struct variable p created?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Action' column in execution_table for variable creation.

If we change p.Name to "Bob", what will be printed at step 4?

A "Bob"

B "Alice"

C 30

D Error

💡 Hint

Refer to variable_tracker to see how changing p.Name affects output.

Concept Snapshot

Accessing struct fields in Go:
- Use dot (.) to get or set fields: variable.field
- Struct variable must be created before access
- Example: p.Name accesses Name field of p
- Fields hold values like strings or ints
- Use fmt.Println to display field values

Full Transcript

This visual trace shows how to access fields of a struct in Go. First, we define a struct type Person with fields Name and Age. Then we create a variable p of type Person with Name set to "Alice" and Age to 30. We access the Name field using p.Name and print it. The dot operator connects the variable to its fields. The variable tracker shows how p and its fields hold values during execution. The program ends after printing "Alice".

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