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Go Structs

A struct is a value that groups named fields of data together. Each field has a name and a type.

A struct type and a value

The Person type groups a name and an age. The dot reads one field at a time.

package main

import "fmt"

type Person struct {
	Name string
	Age  int
}

func main() {
	p := Person{Name: "Hana", Age: 27}
	fmt.Println(p.Name)
	fmt.Println(p.Age)
}

Write a field after creation

The dot also writes a field. The age changes from 22 to 23 after the assignment.

package main

import "fmt"

type Person struct {
	Name string
	Age  int
}

func main() {
	p := Person{Name: "Ana", Age: 22}
	p.Age = 23
	fmt.Println(p.Name, p.Age)
}

Print a struct with %v and %+v

The %v verb prints the values in field order. The %+v verb adds the field names to the same line shape.

package main

import "fmt"

type Person struct {
	Name string
	Age  int
}

func main() {
	p := Person{Name: "Hana", Age: 27}
	fmt.Printf("%v\n", p)
	fmt.Printf("%+v\n", p)
}

A struct inside a struct

The Home field of Employee holds an Address value. Two dots in a row reach the city field inside it.

package main

import "fmt"

type Address struct {
	City string
	Zip  int
}

type Employee struct {
	Name string
	Home Address
}

func main() {
	e := Employee{Name: "Hana", Home: Address{City: "Seattle", Zip: 98101}}
	fmt.Println(e.Home.City)
	fmt.Println(e.Home.Zip)
}

Example

package main

import "fmt"

type Book struct {
	Title  string
	Author string
	Pages  int
}

func main() {
	b := Book{Title: "Go Basics", Author: "Ana Ruiz", Pages: 180}
	fmt.Println("Title:", b.Title)
	fmt.Println("Pages:", b.Pages)
}

Key points

  • Use the type keyword to define a struct and its fields.
  • A field is one named piece of data inside a struct.
  • A struct literal lists a value for each field by field name.
  • Use a dot to read or write a field of a struct value.
  • The %v verb prints the field values in field order.
  • The %+v verb prints the field names beside the values.

In this example, the Book struct groups a title, an author, and a page count. Main builds one Book value with all three fields filled in. The print lines read the title and the page count through the dot.

Try it Yourself

Edit the code, then press Run.

Running is simulated · Go Playground

Exercise

How does code read the Age field of a Person value named p?