Go Fan Out/In Example

main.go

package main

import (
	"fmt"
	"sync"
)

func main() {
	ids := generator("id1", "id2", "id3", "id4", "id5", "id6")

	for r := range merge(fan("one", ids), fan("two", ids), fan("three", ids)) {
		fmt.Println(r)
	}
}

func generator(ids ...string) <-chan string {
	res := make(chan string)
	go func() {
		defer close(res)
		for _, id := range ids {
			res <- id
		}
	}()
	return res
}

func fan(name string, ids <-chan string) <-chan string {
	res := make(chan string)
	go func() {
		defer close(res)
		for id := range ids {
			res <- fmt.Sprintf("fan %s: %s", name, id)
		}
	}()
	return res
}

func merge(chans ...<-chan string) <-chan string {
	var wg sync.WaitGroup
	wg.Add(len(chans))

	res := make(chan string)
	for _, c := range chans {
		go func(c <-chan string) {
			defer wg.Done()
			for n := range c {
				res <- n
			}
		}(c)
	}

	go func() {
		wg.Wait()
		close(res)
	}()

	return res
}