Dependency Injection in Go

Learn dependency injection in go through an executable example, then connect the small demonstration to production code.

Dependency injection means supplying what a component depends on instead of constructing it deep inside that component. Go typically uses constructors, fields and small interfaces rather than a special framework.

The notifier is passed to the service, allowing an in-memory replacement during tests.

Follow this diagram before executing the example. Check where a value or decision changes what runs next.

This example is a complete program. Save it as main.go or paste it into the Go Playground.

Go code

package main

import "fmt"

type Sender interface{ Send(string) error }
type Recorder struct{ Messages []string }

func (r *Recorder) Send(s string) error { r.Messages = append(r.Messages, s); return nil }

type WelcomeService struct{ Sender Sender }

func (w WelcomeService) Welcome(name string) error { return w.Sender.Send("Welcome, " + name) }
func main() {
	recorder := &Recorder{}
	service := WelcomeService{Sender: recorder}
	_ = service.Welcome("Mina")
	fmt.Println(recorder.Messages)
}

Output

[Welcome, Mina]

The injected Recorder records the outgoing message rather than sending email. The service knows only that a Sender can Send a string.

• Inject only dependencies that genuinely vary or complicate tests.
• A nil interface dependency can panic when a method is called; validate required wiring.

Implement a ConsoleSender that prints messages and swap it into WelcomeService.

Tip: Edit the example above, predict the output, and run the modified code to test your reasoning.

You have practiced Dependency Injection in Go in a small, self-contained program. The important habit is to predict what runs, inspect the actual output and distinguish the language rule from the particular example.

Before continuing, make sure you can explain the program to someone who has not seen it, including the line that changes its result.