Receive or Fetch Return Value from a goroutine in Go(Golang)

Channels can be used to fetch return value from a goroutine. Channels provide synchronization and communication between goroutines. You can send the return value in a channel in the goroutine and then collect that value in the main function.

Let’s see a program

package main

import "fmt"

func main() {
	result := make(chan int, 1)
	go sum(2, 3, result)

	value := <-result
	fmt.Printf("Value: %d\n", value)
	close(result)

}

func sum(a, b int, result chan int) {
	sumValue := a + b
	result <- sumValue
	return
}

Output

Value: 5

In the above program we created a variable result which is a channel of length 1 holding value of int type. We passed this channel to the sum function. The sum function pushes the sumValue to the result channel like this

result <- sumValue

The in the main function we are waiting on the result channel to collect the result

value := <-result

This line will wait until a value is pushed to the result channel. As seen above the sumValue will be pushed to result channel by the function sum.

To illustrate that this line will actually wait let's put a timeout in the sum function it actually pushes sumValue to the result channel

package main

import (
	"fmt"
	"time"
)

func main() {
	result := make(chan int, 1)
	go sum(2, 3, result)

	value := <-result
	fmt.Printf("Value: %d\n", value)
	close(result)

}

func sum(a, b int, result chan int) {
	sumValue := a + b
	time.Sleep(time.Second * 2)
	result <- sumValue
	return
}

Output

Value: 5

The program gives the same output which proves that the main function waits for sumValue to be pushed to the result channel. Once it receives the value from the result channel, it prints it.