Structs in Go

# CHAPTER 14

Structs in Go #

1. Introduction #

In Java or Python, you would use a Class. Go does NOT have classes. Instead, Go uses Structs. Structs form the entire foundation of Object-Oriented Programming (OOP) in Go.

2. Learning Objectives #

• Define a custom Struct type.

• Instantiate and initialize Structs.

• Access and modify Struct fields.

• Pass Structs using pointers.

• Understand Composition using Embedded Structs.

3. Defining and Using a Struct #

package main
import "fmt"

// 1. Define the Struct (Usually outside the main function)
type Employee struct {
    ID     int
    Name   string
    Salary float64
    IsLead bool
}

func main() {
    // 2. Instantiate using named fields (Best Practice)
    emp1 := Employee{
        ID:     101,
        Name:   "Alice",
        Salary: 85000.00,
        IsLead: true, // Note the trailing comma!
    }

    // 3. Accessing fields using the dot (.) operator
    fmt.Println("Employee Name:", emp1.Name)
    
    // Modifying a field
    emp1.Salary = 90000.00
}

4. Zero Values in Structs #

emp2 := Employee{Name: "Bob"}
fmt.Println(emp2.ID) // Prints 0
fmt.Println(emp2.IsLead) // Prints false

5. Passing Structs (Pointers are Critical!) #

// Accepts a pointer to an Employee
func GiveRaise(emp *Employee) {
    emp.Salary += 5000 
    // Notice we use emp.Salary, not (*emp).Salary. 
    // Go automatically dereferences struct pointers for you!
}

func main() {
    emp := Employee{Name: "Charlie", Salary: 50000}
    
    GiveRaise(&emp) // Pass the memory address
    fmt.Println(emp.Salary) // 55000
}

6. Embedded Structs (Composition over Inheritance) #

type Address struct {
    City  string
    State string
}

type User struct {
    Name    string
    Contact Address // Embedded Struct
}

func main() {
    u := User{
        Name: "David",
        Contact: Address{
            City:  "New York",
            State: "NY",
        },
    }

    // Access nested fields
    fmt.Println(u.Contact.City) // Prints "New York"
}

7. Anonymous Structs #

config := struct {
    Port int
    Env  string
}{
    Port: 8080,
    Env:  "Production",
}
fmt.Println(config.Port)

8. Common Mistakes #

• Trailing Commas: When initializing a multi-line struct, Go strictly requires a comma , after the very last field. If you omit it, the code will not compile.

• Assuming Inheritance: Trying to cast an embedded struct to its parent struct. Go is not an OOP language in the traditional sense; do not try to force Java-style hierarchies.

9. Best Practices #

• Always use Named Fields during initialization (Employee{Name: "Bob"}). It prevents bugs if you later add new fields to the struct definition.

10. Exercises #

1. 1. Define a Car struct with fields Make, Model, and Year.

1. 2. Instantiate a Car object and print its Make.

1. 3. Create an UpdateYear function that takes a pointer to a Car and changes the year. Test it.

11. MCQs with Answers & Explanations #

Q1. Does Go have traditional Classes? a) Yes b) No Answer: b) No. *Explanation: Go uses Structs to group data.*

12. Interview Preparation #

1. 1. Go does not have Classes or Inheritance. How does it achieve Object-Oriented modeling?

1. 2. Explain Composition over Inheritance and provide a brief code example.

13. Summary #

14. Next Chapter Recommendation #