Or Done channel - Concurrency in Go Book

OrDoneChannel.go

package main

import (
	"fmt"
	"time"
)

// Simpler version for Or
func OrVer2(ch ...chan struct{}) <-chan struct{} {
	switch len(ch) {
	case 0:
		return nil
	case 1:
		return ch[0]
	}
	
	orDone := make(chan struct{})
	
	go func() {
		defer close(orDone)
		
		switch len(ch) {
		case 2:
			select {
			case <-ch[0]:
			case <-ch[1]:
			}
		default:
			select {
			case <-ch[0]:
			case <-ch[1]:
			case <-OrVer2(ch[2:]...):
			}
		}
	}()
	
	return orDone
}

func Or(ch ...chan struct{}) <-chan struct{} {
	switch len(ch) {
	case 0:
		return nil
	case 1:
		return ch[0]
	}
	
	orDone := make(chan struct{})
	
	go func() {
		defer close(orDone)
		
		switch len(ch) {
		case 2:
			select {
			case <-ch[0]:
			case <-ch[1]:
			}
		default:
			select {
			case <-ch[0]:
			case <-ch[1]:
			case <-ch[2]:
			case <-Or(append(ch[3:], orDone)...):
			}
		}
	}()
	
	return orDone
}

func closeAfter(duration time.Duration) chan struct{} {
	c := make(chan struct{})
	go func() {
		defer close(c)
		time.Sleep(duration)
	}()
	return c
}

func main()  {
	startTime := time.Now()
	<-OrVer2(
		closeAfter(time.Hour),
		closeAfter(time.Minute),
		closeAfter(time.Second),
		closeAfter(2*time.Second),
		closeAfter(3*time.Second),
		closeAfter(1*time.Second),
		closeAfter(2*time.Second),
		closeAfter(3*time.Minute),
		closeAfter(5*time.Millisecond),
		closeAfter(3*time.Second),
		closeAfter(30*time.Second),
		closeAfter(3*time.Second),
		closeAfter(2*time.Second),
		)
	
	fmt.Println("Done in ", time.Since(startTime))
}