gist 4 https://medium.com/@francesc/two-ways-of-merging-n-channels-in-go-43c0b57cd1de

main.go

func merge(cs ...<-chan int) <-chan int {
	out := make(chan int)
	var wg sync.WaitGroup
	wg.Add(len(cs))
	for _, c := range cs {
		go func(c <-chan int) {
			for v := range c {
				out <- v
			}
			wg.Done()
		}(c)
	}
	go func() {
		wg.Wait()
		close(out)
	}()
	return out
}