the go dic

Golang Dependency Injection Contaner

To manage the responsibility of dependency creation, each Go application should have a service locator that is responsible for construction and lookup of dependencies.

Asking for dependencies solves the issue of hard coding, but it also means that the dic needs to be passed throughout the application. Passing the injector breaks the Law of Demeter.

To remedy this, you could inject to a service only the dependency it needs.

Benefits

• More Reusable Code
• More Testable Code
• More Readable Code

Example...

see example folder, you could run with

run go run example/example.go and go run example/example_struct.go

Injecting deps on structs

type mailer struct {
	Logger string `dic:"log"`
	Transport Transport `dic:"transport.sendmail"`
}
mailer = new(mailer)
cnt := container.New()

cnt.Register("output_writer", os.Stdout)
cnt.Register("log", log.New, reference.New("output_writer"), "", log.Ldate|log.Lmicroseconds|log.Lshortfile)
cnt.Register("transport.sendmail", SendmailNew /*, lot of arguments*/)

cnt.inject(mailer)
mailer.Transport.Send()
mailer.Logger.Println("hello log")

Services

Injection of dependencies into controllers

cnt := container.New()
cnt.Register("logger", log.New /*, lot of arguments*/)
cnt.Register("template.path", "template/")
cnt.Register("template", abcTemplate.new, reference.New("template.path"), reference.New("logger"))

cnt.Register("transport.sendmail", SendmailNew /*, lot of arguments*/)
cnt.Register("mailer", MailerNew, reference.New("transport"), "[golangit] ")

// injecting into controller
cnt.Register("controller_home", func (logger Logger, mailer Mailer) {/*do something*/}, reference.New("logger"), reference.New("mailer"))

cnt.Register("controller_admin", func (tpl Template, mailer Mailer) {/*do something*/}, reference.New("template"), reference.New("mailer"))

Registering Structs and parameters

type TestStruct struct {
	dbName string
	logger Logger    
}

cnt := container.New()
// Storing pareter
cnt.Register("log.filename", "error.log")
cnt.Register("db.name", "logger-database")
// storing service
cnt.Register("logger", LoggerNew, reference.New("log.filename"))
cnt.Register("context", &TestStruct{}, reference.New("db.name"), reference.New("logger"))

test := cnt.Get("context").(TestStruct)
// now struct has .dbName = 'logger-database' and the logger is an object wht the filename injected

API

Register stores functions, structs or parameters into the service locator.

Get resolves dependencies and return the value.

Inject

Everything is injected with lazy injection.

Easy multiple env.

cnt := container.New()
if env == "prod" {
	cnt.Register("transport.sendmail", SendmailNew /*, lot of arguments*/)
} else {
   cnt.Register("transport.sendmail", StubMailNew)
}

Create a not public service

Is possible to create a service usable only as dependency

def := definition.New(SendmailNew).setPublic(false)
cnt.Register("transport.sendmail", def)

Create a not static service

All the service are served statically, this means that the service is executed only once.

def := definition.New(SendmailNew).setStatic(false)
cnt.Register("transport.sendmail", def)

Injecting using tagging (annotation)

cnt.Register("mail.prefix", "[golangit] ")

type mailer struct {
	Sender     MailSender `dic:"transport.sendmail"`
	MailPrefix string     `dic:"mail.prefix"`
}

mailer := &mailer
cnt.Inject(mailer) //mailer has now dependencies injected
mailer.Sender.Send()

Test

This library has been developed with ginkgo a BDD Testing Framework for Go,

Install the dependencies:

go get -v -t ./...
go get -v github.com/onsi/ginkgo
go get -v github.com/onsi/gomega
go install -v github.com/onsi/ginkgo/ginkgo

Run all the bdd tests:

ginkgo -r

License

MIT License

Thanks to

Symfony dependency injection container

Spring service container

@mikespook bind function

ToDo

1. alias
2. Cli for debugging
3. godoc
4. improving injection