In this subsection, you will learn how to read from a channel. You can read a single value from a channel named c by executing <-c. In this case, the direction is from the channel to the outer world.

The name of the program that I will use to help you understand how to read from a channel is readCh.go, and it will be presented in three parts.

The first code segment from readCh.go is shown in the following Go code:

package main 
 
import ( 
    "fmt" 
    "time" 
) 
 
func writeToChannel(c chan int, x int) { 
    fmt.Println("1", x) 
    c <- x 
    close(c) 
    fmt.Println("2", x) 
} 

The implementation of the writeToChannel() function is the same as before.

The second part of readCh.go follows next:

func main() { 
    c := make(chan int) 
    go writeToChannel(c, 10) 
    time.Sleep(1 * time.Second) 
    fmt.Println("Read:", <-c) 
    time.Sleep(1 * time.Second) 

In the preceding code, you read from the c channel using the <-c notation. If you want to store that value to a variable named k instead of just printing it, you can use a k := <-c statement. The second time.Sleep(1 * time.Second) statement gives you the time to read from the channel.

The last code portion of readCh.go contains the following Go code:

    _, ok := <-c 
    if ok { 
        fmt.Println("Channel is open!") 
    } else { 
        fmt.Println("Channel is closed!") 
    } 
} 

In the preceding code, you can see a technique for determining whether a given channel is open or not. The current Go code works fine when the channel is closed; however, if the channel were open, the Go code presented here would have discarded the read value of the channel because of the use of the _ character in the _, ok := <-c statement. Use a proper variable name instead of _ if you also want to read the value of the channel in case it is open.

Executing readCh.go will generate the following output:

$ go run readCh.go
1 10
Read: 10
2 10
Channel is closed!
$ go run readCh.go
1 10
2 10
Read: 10
Channel is closed!  

Although the output is still not deterministic, both the fmt.Println(x) statements of the writeToChannel() function are executed because the channel is unblocked when you read from it.