Example of github.com/facebookgo/inject for dummies (like me).

inject_example.go

package main
​
import (
	"fmt"
	"github.com/facebookgo/inject"
	"strings"
)
​
type ILog interface {
	Log(string)
}
​
//------------------------------------------------------------------------------
​
// IVehicle describes ...
type IVehicle interface {
	MinimumAge() int
	Wheels() int
}
​
type ILicenseCheck interface {
	CanDrive(Person, IVehicle) bool
}
​
type DefaultLicenseCheck struct {}
​
func (d *DefaultLicenseCheck) CanDrive(p Person, v IVehicle) bool {
	return p.Age >= v.MinimumAge()
}
​
//------------------------------------------------------------------------------
​
// Car is ...
type Car struct {
	Log    ILog `inject:""`
	engine string
	wheels int
}
​
// NewCar creates ...
func NewCar() *Car {
	return &Car{wheels: 4}
}
​
// Wheels return ...
func (c *Car) Wheels() int {
	c.Log.Log("Car wheels")
	return c.wheels
}
​
func (c *Car) MinimumAge() int {
	return 16
}
​
//------------------------------------------------------------------------------
​
// Bike is ...
type Bike struct {
	Log    ILog `inject:""`
	wheels int
}
​
// NewBike creates ...
func NewBike() *Bike {
	return &Bike{wheels: 2}
}
​
// Wheels return ...
func (b *Bike) Wheels() int {
	b.Log.Log("Bike wheels")
	return b.wheels
}
​
func (b *Bike) MinimumAge() int {
	return 4
}
​
//------------------------------------------------------------------------------
​
// Person is ...
type Person struct {
	Vehicle IVehicle `inject:""`
	Log     ILog `inject:""`
	LicenseCheck ILicenseCheck `inject:""`
	Age int
}
​
// NewPerson creates ...
func NewPerson(age int) *Person {
	return &Person{
		Age: age,
	}
}
​
func (person *Person) Drive() {
	if !person.LicenseCheck.CanDrive(*person, person.Vehicle) {
		person.Log.Log("Waah! I can't drive this yet!")
	} else {
		person.Log.Log(fmt.Sprintf("Driving around on %d wheels", person.Vehicle.Wheels()))
	}
}
​
//------------------------------------------------------------------------------
​
type ConsoleLog struct {
}
​
func (consoleLog *ConsoleLog) Log(info string) {
	fmt.Println(info)
}
​
//==============================================================================
​
var (
	person = NewPerson(12)
	car = NewCar()
	bike = NewBike()
)
​
func init() {
	log := &ConsoleLog{}
	licenseCheck := &DefaultLicenseCheck{}
	inject.Populate(person, log, car, licenseCheck)
}
​
func main() {
	person.Drive()
	mockTest()
}
​
type MockILicenseCheck struct {
	timesCalled int
	WhatToReturn bool
}
​
func (m *MockILicenseCheck) CanDrive(p Person, v IVehicle) bool {
	m.timesCalled++
	return m.WhatToReturn
}
​
func (m *MockILicenseCheck) Reset() {
	m.timesCalled = 0
}
​
type MockILog struct {
	timesCalled int
	LastMessage string
}
​
func (m *MockILog) Log(value string) {
	m.timesCalled++
	m.LastMessage = value
}
​
func (m *MockILog) Reset() {
	m.timesCalled = 0
	m.LastMessage = ""
}
​
func mockTest() {
	log := &MockILog{}
	licenseCheck := &MockILicenseCheck{WhatToReturn: true}
	p := NewPerson(12)
	b := NewBike()
	inject.Populate(log, licenseCheck, b, p)
	p.Drive()
	fmt.Printf("Expect 1, actual %d\n", licenseCheck.timesCalled)
	fmt.Printf("Expect false, actual %t\n", strings.HasPrefix(log.LastMessage, "Waah"))
	log.Reset()
	licenseCheck.Reset()
	licenseCheck.WhatToReturn = false
	p.Drive()
	fmt.Printf("Expect true, actual %t\n", strings.HasPrefix(log.LastMessage, "Waah"))
}