go中的单向通道

青旅半醒 2022-03-26 11:48 156阅读 0赞

//chan只能接收，无法发送
    	var uselessChan = make(chan<- int, 1)
    	uselessChan <-1
    	i:=<-uselessChan// invalid operation: <-uselessChan (receive from send-only type chan<- int)
    	fmt.Println(i)
    
    	//chan只能发送，无法接收
    	var uselessChan2 = make(<-chan int, 1)
    	j:=<-uselessChan2
    	fmt.Println(j)
    	uselessChan2 <-9//invalid operation: uselessChan2 <- 9 (send to receive-only type <-chan int)

for读取信道内容:

//返回值为单向通道
    func main() {
    	intChan2 := getIntChan()
    	/**
    	for会一直尝试读取channel里面的值，如果 channel的值为nil，会阻塞在for关键字的一行
    	 */
    	for elem := range intChan2 {
    		fmt.Printf("The element in intChan2: %v\n", elem)
    	}
    	/**
    	The element in intChan2: 0
    	The element in intChan2: 1
    	The element in intChan2: 2
    	The element in intChan2: 3
    	The element in intChan2: 4
    	 */
    
    }
    
    func getIntChan() <-chan int {
    	num := 5
    	ch := make(chan int, num)
    	for i := 0; i < num; i++ {
    		ch <- i
    	}
    	close(ch)
    	return ch
    }

如果在select语句中发现某个通道已关闭，那么应该怎样屏蔽掉它所在的分支？

func main() {
    
    	intChannels := make(chan int, 2)
    
    	intChannels <- 1
    	intChannels <- 2
    
    	for {
    		// 哪一个通道中有可取的元素值，哪个对应的分支就会被执行。
    		select {
    		case _,ok:=<-intChannels:
    			fmt.Println("The first candidate case is selected.")
    		if(!ok){
    			intChannels = make(chan int)
    		}
    
    		default:
    			fmt.Println("default.")
    		}
    		time.Sleep(time.Duration(2)*time.Second)
    	}
    	/**
    	输出结果:
    	The first candidate case is selected.
    The first candidate case is selected.
    default.
    default.
    default.
    default.
    	 */
    
    }

在select语句与for语句联用时，怎样直接退出外层的for语句？

func main() {
    
    
    		// 准备好几个通道。
    		intChannels := [3]chan int{
    			make(chan int, 2),
    			make(chan int, 2),
    			make(chan int, 2),
    		}
    
    	loop:
    	for  {
    		// 随机选择一个通道，并向它发送元素值。
    		index := rand.Intn(3)
    		fmt.Printf("The index: %d\n", index)
    		intChannels[index] <- index
    		// 哪一个通道中有可取的元素值，哪个对应的分支就会被执行。
    		select {
    		case <-intChannels[0]:
    			fmt.Println("The first candidate case is selected.")
    			break loop
    		case <-intChannels[1]:
    			fmt.Println("The second candidate case is selected.")
    		case elem := <-intChannels[2]:
    			fmt.Printf("The third candidate case is selected, the element is %d.\n", elem)
    		default:
    			fmt.Println("default case is selected!")
    		}
    	}
    
    	fmt.Println("end")
    
    
    }
    /**
    The index: 2
    The third candidate case is selected, the element is 2.
    The index: 0
    The first candidate case is selected.
    end
     */