golang reflect.Select 用法

package main
 
import (
    "fmt"
    "reflect"
    "strconv"
)
 
func main() {
    var chs1 = make(chan int)
    var chs2 = make(chan float64)
    var chs3 = make(chan string)
    var ch4close = make(chan int)
    defer close(ch4close)
 
    go func(c chan int, ch4close chan int) {
        for i := 0; i < 5; i++ {
            c <- i
        }
        close(c)
        ch4close <- 1
    }(chs1, ch4close)
 
    go func(c chan float64, ch4close chan int) {
        for i := 0; i < 5; i++ {
            c <- float64(i) + 0.1
        }
        close(c)
        ch4close <- 1
    }(chs2, ch4close)
 
    go func(c chan string, ch4close chan int) {
        for i := 0; i < 5; i++ {
            c <- "string:" + strconv.Itoa(i)
        }
        close(c)
        ch4close <- 1
    }(chs3, ch4close)
 
 
    var selectCase = make([]reflect.SelectCase, 4)
    selectCase[0].Dir = reflect.SelectRecv
    selectCase[0].Chan = reflect.ValueOf(chs1)
 
    selectCase[1].Dir = reflect.SelectRecv
    selectCase[1].Chan = reflect.ValueOf(chs2)
 
    selectCase[2].Dir = reflect.SelectRecv
    selectCase[2].Chan = reflect.ValueOf(chs3)
 
    selectCase[3].Dir = reflect.SelectRecv
    selectCase[3].Chan = reflect.ValueOf(ch4close)
 
    done := 0
    finished := 0
    for finished < len(selectCase)-1 {
        chosen, recv, recvOk := reflect.Select(selectCase)
 
        if recvOk {
            done = done+1
            switch chosen {
            case 0:
                fmt.Println(chosen, recv.Int())
            case 1:
                fmt.Println(chosen, recv.Float())
            case 2:
                fmt.Println(chosen, recv.String())
            case 3:
                finished = finished+1
                done = done-1
                // fmt.Println("finished\t", finished)
            }
        }
    }
    fmt.Println("Done", done)
 
}