Embedding Types To Share Functionality In Go

Use embedding to share functionality between types in Go.

Both car and boat embed the type vehicle. Because they do that, they get access to the method move on vehicle automatically. Pretty nice!

As stated in the golang docs:

Go does not provide the typical, type-driven notion of subclassing, but it does have the ability to “borrow” pieces of an implementation by embedding types within a struct or interface.

This is similar to subclassing as you might be familiar with it in other languages. Neither boat nor car are classes, but the abilities gained by embedding are very similar.

package main

import (
	"fmt"
)

func main() {
	car := &car{}
	car.move()

	boat := &boat{}
	boat.move()
}

type vehicle struct {
}

func (v vehicle) move() {
	fmt.Println("I am a vehicle! I move!")
}

type car struct {
	vehicle
	wheels int
}

type boat struct {
	vehicle
	rudders int
}

// With this commented out, invoking car.move() will call the method
// `func (v vehicle) move() {}` instead.
// func (c car) move() {
// 	fmt.Println("I am a car! I drive!")
// }

func (b boat) move() {
	fmt.Println("I am a boat! I sail!")
}

This produces the following output.

I am a vehicle! I move!
I am a boat! I sail!