golang 函数返回chan类型的操作

// Messages returns the read channel for the messages that are returned by
// the broker.
//
// This channel will only return if Config.Group.Mode option is set to
// ConsumerModeMultiplex (default).
func (c *Consumer) Messages() <-chan *sarama.ConsumerMessage { return c.messages }

package main
import (
    "fmt"
)
type C struct {
    Name string
}
type D struct {
    Id chan C
}
func (d *D)A() chan C {
    return d.Id
}
func main() {
    c := C{
        Name: "test",
    }
    ch := make(chan C, 10)
    ch <- c
    d := D{
        Id: ch,
    }
    r := d.A()
    r <- c
    for i:=0;i<=len(r);i++ {
        fmt.Printf("%v", <-r)
    }
}

{test}{test}
Process finished with exit code 0

package main
import (
    "fmt"
)
type C struct {
    Name string
}
type D struct {
    Id chan C
}
func (d *D)A() <-chan C {
    return d.Id
}
func main() {
    c := C{
        Name: "test",
    }
    ch := make(chan C, 10)
    ch <- c
    d := D{
        Id: ch,
    }
    r := d.A()
    r <- c
    for i:=0;i<=len(r);i++ {
        fmt.Printf("%v", <-r)
    }
}

# command-line-arguments
.\test2.go:29:7: invalid operation: r <- c (send to receive-only type <-chan C)
Compilation finished with exit code 2

var ch1 chan<- int  // 声明ch1，只用于写int数据
var ch2 <-chan int  // 声明ch2，只用于读int数据

ch3 := make(chan<- int, 10)  // 初始化一个只写的channel
ch4 := make(<-chan int, 10)  // 初始化一个只读的chaannel