Go Tutorial · Data Structures · Lesson 15 of 30

Go Structs

Group fields into structs, struct literals, embedding and tags.

Defining structs

A struct groups named fields — Go's way of modelling data (there are no classes):

Example 1

package main

import "fmt"

type User struct {
	Name  string
	Email string
	Age   int
}

func main() {
	u := User{Name: "Ada", Email: "[email protected]"}
	u.Age = 36
	fmt.Println(u.Name, u.Age)
	fmt.Printf("%+v\n", u)

	anon := struct {
		X, Y int
	}{3, 4}
	fmt.Println(anon)

	p := &u // pointer to struct: fields accessed the same way
	p.Age++
	fmt.Println(u.Age)
}

Output

Ada 36
{Name:Ada Email:[email protected] Age:36}
{3 4}
37

Run this on your computer — see “Get Started” for setup.

Embedding

Embedding a struct promotes its fields and methods — composition instead of inheritance:

Example 2

package main

import "fmt"

type Person struct {
	Name string
	City string
}

func (p Person) Greet() string {
	return "Hi, I'm " + p.Name
}

type Employee struct {
	Person // embedded
	Title  string
}

func main() {
	e := Employee{Person: Person{Name: "Lin", City: "Oslo"}, Title: "Engineer"}
	fmt.Println(e.Name, e.City, e.Title) // promoted fields
	fmt.Println(e.Greet())               // promoted method
}

Output

Lin Oslo Engineer
Hi, I'm Lin

Run this on your computer — see “Get Started” for setup.

Struct tags

Tags are metadata read by packages like encoding/json: `json:"name"` — see JSON.

Test yourself

What does Go use instead of class inheritance?

extends
Embedding (composition)
Prototypes
Mixins

Show answer

Answer: Embedding (composition)