函数调用中带有参数的传递类型

Question

The code below is from Jan Newmarch's book about network programming in Go. In most of the Go code that I've seen (which is very little, as I'm a newbie, you don't (in a function call) pass a type with a parameter. However, in the code below, you see this line

conn.Write([]byte(daytime))

Why is it necessary to include []byte in this function call?

func main() {

    service := ":1200"
    tcpAddr, err := net.ResolveTCPAddr("ip4", service)
    checkError(err)

    listener, err := net.ListenTCP("tcp", tcpAddr)
    checkError(err)

    for {
        conn, err := listener.Accept()
        if err != nil {
            continue
        }

        daytime := time.Now().String()
        conn.Write([]byte(daytime))

Answer 1

Conn.Write() expects the value as a byte slice. Since daytime is of type string you have to convert it.

You could rewrite the above as:

daytime := []byte(time.Now().String())
conn.Write(daytime)

Or, as @fabrizioM writes, you could use the formatted writer which would convert it:

fmt.Fprintf(conn, daytime)