Range over Channels

In an earlier example we saw how for and range provide iteration over basic data structures. We can also use this syntax to iterate over values received from a channel.

package main

import "fmt"

gen returns a channel and a goroutine that fills it, closing it when done. This generator shape is very common.

func gen(nums ...int) <-chan int {
	out := make(chan int)
	go func() {
		defer close(out)
		for _, n := range nums {
			out <- n
		}
	}()
	return out
}

func main() {

We'll iterate over 2 values in the queue channel.

	queue := make(chan string, 2)
	queue <- "one"
	queue <- "two"
	close(queue)

This range iterates over each element as it's received from queue. Because we closed the channel above, the iteration terminates after receiving the 2 elements.

	for elem := range queue {
		fmt.Println(elem)
	}

This example also showed that it's possible to close a non-empty channel but still have the remaining values be received.

	total := 0
	for n := range gen(1, 2, 3, 4) {
		total += n
	}
	fmt.Println("total:", total)
}

$ go run ./41_range_over_channels
one
two
total: 10

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