只读通道，是无需关闭的吗？调用 close 函数会报错

// The close built-in function closes a channel, which must be either
// bidirectional or send-only. It should be executed only by the sender,
// never the receiver, and has the effect of shutting down the channel after
// the last sent value is received. After the last value has been received
// from a closed channel c, any receive from c will succeed without
// blocking, returning the zero value for the channel element. The form
//
//    x, ok := <-c
//
// will also set ok to false for a closed and empty channel.
func close(c chan<- Type)Copy