从一个有缓冲的 channel 里读数据，当 channel 被关闭，依然能读出有效值。只有当返回的 ok 为 false 时，读出的数据才是无效的。 ``` func main() { ch := make(chan int, 5) ch <- 18 close(ch) x, ok := <-ch if ok { fmt.Println("received: ", x) } x, ok = <-ch if !ok { fmt.Println("channel closed, data invalid.") } //写入管道，会报错。panic: send on closed channel // ch <- 11 } ``` 运行结果： > received: 18 > channel closed, data invalid.