fx

• Makes dependency injection easy.

• Eliminates the need for global state and func init().

What is dependency injection?

No dependency injection

public SomeClass() {
    myObject = Factory.getObject();
}

// from https://www.youtube.com/watch?v=LDGKQY8WJEM&t=254s&ab_channel=UberEngineering
func NewHandler() http.Handler {
	logger := log.New(os.Stdout, "[ACME] ", 0)
	// user logger
}

With dependency injection

public SomeClass (MyClass myObject) {
    this.myObject = myObject;
}

// from https://www.youtube.com/watch?v=LDGKQY8WJEM&t=254s&ab_channel=UberEngineering
func NewHandler(logger *log.Logger) http.Handler {
	// use logger
}

Why do we need dependency injection?

• Easy to test

• Decouple your objects

fx.New

// kick start your app
fx.New().Run()

fx.Provide

// Constructs type *C, depends on *A and *B.
func(*A, *B) *C

// Constructs type *C, depends on *A and *B, and indicates failure by
// returning an error.
func(*A, *B) (*C, error)

// Constructs types *B and *C, depends on *A, and can fail.
func(*A) (*B, *C, error)

fx.New(
	fx.Provide(http.NewServeMux),
).Run()

fx.Invoke

fx.New(
	fx.Provide(http.NewServeMux),
	fx.Invoke(server.New)
).Run()

How does a function get invoked?

• Always executed when starting the application

• Executed in order

What inputs or outputs are needed for a function?

Arguments for these invocations are built using the constructors registered by Provide.

fx.Hook

fx.Hook{
	OnStart: func(ctx context.Context) error {
		log.Println("Start running...")
	}, 
	OnStop: func(ctx context.Context) error {				
		log.Println("Stop running...")
	},
}

fx.App

fx.App.Start and fx.App.Stop

app := fx.New()
app.Start()
app.Stop()

fx.App.Run

app := fw.New()
app.Run()

Example

Source