Create a minimal application

Let's build the hello-world equivalent of an Fx application. This application won't do anything yet except print a bunch of logs.

1. Write a minimal main.go.

   package main
   
   import "go.uber.org/fx"
   
   func main() {
     fx.New().Run()
   }
   

2. Run the application.

   go run .
   

   You'll see output similar to the following.

   [Fx] PROVIDE    fx.Lifecycle <= go.uber.org/fx.New.func1()
   [Fx] PROVIDE    fx.Shutdowner <= go.uber.org/fx.(*App).shutdowner-fm()
   [Fx] PROVIDE    fx.DotGraph <= go.uber.org/fx.(*App).dotGraph-fm()
   [Fx] RUNNING
   

   This shows the default objects provided to the Fx application, but it doesn't do anything meaningful yet. Stop the application with Ctrl-C.

   [Fx] RUNNING
   ^C
   [Fx] INTERRUPT
   

What did we just do?

We built an empty Fx application by calling fx.New with no arguments. Applications will normally pass arguments to fx.New to set up their components.

We then run this application with the App.Run method. This method blocks until it receives a signal to stop, and it then runs any cleanup operations necessary before exiting.

Fx is primarily intended for long-running server applications; these applications typically receive a signal from the deployment system when it's time to shut down.