merge_chans.go

package main

import (
	"fmt"
	"time"
)

func mergeWithRange(chans ...chan int) chan int {
	out := make(chan int)

	for _, ch := range chans {
		go func(c chan int) {
			for v := range c {
				out <- v
			}
		}(ch)
	}
	
	
	// create a closeChan 

	return out

}

func mergeWithSelect(chans ...chan int) chan int {
	outch := make(chan int)
	closeChan := make(chan struct{})

	for _, ch := range chans {
		go func(c chan int) {
			for {
				v, ok := <-c
				if !ok {
					closeChan <- struct{}{}

					return
				}

				outch <- v
			}

		}(ch)
	}

	go func(outChan chan int, closeChan chan struct{}, chanCount int) {
		counter := 0

		for {
			<-closeChan
			counter++

			if counter == chanCount {
				close(outChan)
			}
		}
	}(outch, closeChan, len(chans))

	return outch
}

func main() {
	a := make(chan int)
	b := make(chan int)
	c := make(chan int)

	res := mergeWithSelect(a, b, c)

	go func() {
		for v := range res {
			fmt.Println(v)
		}

		println("close!")
	}()

	a <- 1
	b <- 2
	a <- 3

	close(a)
	close(b)
	close(c)

	time.Sleep(time.Second * 3)

}