Lesson 8: Structs¶

Big Picture¶

classDiagram
    class Person {
        +string Name
        +int Age
        +Greet() string
        +Birthday()
    }
    class Employee {
        +float64 Salary
        +GiveRaise(pct float64)
    }
    Person <|-- Employee : embeds (composition)
    note for Person "value receiver copies · pointer receiver mutates"

Go has no classes and no inheritance — structs + methods + embedding give you composition instead. Use a pointer receiver when the method should mutate the struct (or to avoid copying a big struct).

Concepts¶

Defining Structs¶

type Person struct {
    Name string
    Age  int
}

Creating Instances¶

p := Person{Name: "Alice", Age: 25}
p := Person{"Alice", 25}  // Positional
p := &Person{Name: "Bob"} // Pointer

Methods¶

// Value receiver
func (p Person) Greet() string {
    return "Hello, " + p.Name
}

// Pointer receiver (can modify)
func (p *Person) Birthday() {
    p.Age++
}

Embedding¶

type Employee struct {
    Person        // Embedded
    Salary float64
}
// emp.Name works (promoted)

Code Walkthrough¶

package main

import "fmt"

type Person struct {
    Name string
    Age  int
}

func (p Person) Greet() string { return "Hi " + p.Name }
func (p *Person) Birthday()    { p.Age++ } // mutates

func main() {
    p := Person{Name: "Alice", Age: 30}
    fmt.Println(p.Greet())
    p.Birthday()
    fmt.Println(p.Age) // 31
}

Full program: code/08_structs.go.

cd code
go run . structs

Check Your Understanding¶