go_concurrency.say_hello_5.main.go

package main

import (
	"fmt"
	"sync"
)

func main() {
	wg := sync.WaitGroup{} // 1. Create a WaitGroup
	wg.Add(1) // 2. Add 1 to WaitGroup counter

	go func(){
		fmt.Println("Hello world!")

		wg.Done() // 4. Inform 1 goroutine finished
	}()

	wg.Wait() // 3. Tell main() to wait until all goroutines finished
}