I'm pretty sure I'm writing unidiomatic go. But the official docs claim that structs work like OO classes do.

forcing_oop_in.go

// You have to have your GOPATH and all that set up for this source file separation
// to work.  I was playing with source file organization at the same time.
// If this is too annoying, I can rework it.


// car/car.go

package main

import (
  "car/parts"
	"fmt"
)

var color string = "blue"

type Warranty struct {
	years int
	miles float32
}

type Car struct {
	sMake  string
	model  string
	// doors  []parts.Door  // forget about this for now
	engine *parts.Engine
}

func init() { // optional init of package
	// var v6 = &parts.Engine{6, false}
}

func main() {
	car := Car{
		sMake:  "Ford",
		model:  "Mustang",
		engine: &parts.Engine.NewEngine(6),
	}
	fmt.Printf("I'm going to work now in my %s %s\n", car.sMake, car.model)

	fmt.Println("I guess I should start my car.")
	car.Start()
	fmt.Println("Engine started?", car.engine.IsStarted())
}

func (car Car) Start() {
	fmt.Println("starting engine ...")
	car.engine.Start()
	fmt.Println("you'd think it would be started here ...", car.engine)
}


// car/parts/engine.go
package parts

import (
  "fmt"
)

type Engine struct {
	cylinders int
	started   bool
}

// go does not have explicit constructors
func NewEngine(cylinders int) *Engine {
	return &Engine{cylinders: cylinders, started: false}
}

func (engine Engine) Start() {
	fmt.Println("ENGINE STARTED", engine.started)
	engine.started = true
	fmt.Println("ENGINE STARTED", engine.started)
}

func (engine Engine) IsStarted() bool {
	return engine.started
}