Go by Example: Channel Directions

When using channels as function parameters, you can specify if a channel is meant to only send or receive values. This specificity increases the type-safety of the program.

package main
import "fmt"

This ping function only accepts a channel for sending values. It would be a compile-time error to try to receive on this channel.

func ping(pings chan<- string, msg string) {
    pings <- msg

The pong function accepts one channel for receives (pings) and a second for sends (pongs).

func pong(pings <-chan string, pongs chan<- string) {
    msg := <-pings
    pongs <- msg
func main() {
    pings := make(chan string, 1)
    pongs := make(chan string, 1)
    ping(pings, "passed message")
    pong(pings, pongs)
$ go run channel-directions.go
passed message

Next example: Select.