Channels

A channel is a typed pipe for sending values between goroutines. msg := <-messages blocks until a value is sent on that channel, which is exactly how the two goroutines in the example below coordinate without any shared variable or lock.

package main

import "fmt"

func main() {
	messages := make(chan string)

	go func() {
		messages <- "hello from a goroutine"
	}()

	msg := <-messages
	fmt.Println(msg)
}

hello from a goroutine

A real example: summing concurrently

sum runs as its own goroutine and sends its result back over result once it's done — main blocks on <-result until that value arrives. This channel-based handoff is Go's idiomatic alternative to manually sharing memory between goroutines and protecting it with locks.

package main

import "fmt"

func sum(numbers []int, result chan<- int) {
	total := 0
	for _, n := range numbers {
		total += n
	}
	result <- total
}

func main() {
	result := make(chan int)
	go sum([]int{1, 2, 3, 4, 5}, result)
	fmt.Println(<-result)
}

15

Next: struct embedding — Go's way of building composition instead of class inheritance.