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)
    fmt.Println(<-pongs)
}

$ go run channel-directions.go
passed message