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The ➰Select➰ keyword in Golang

chseki profile image Christian Seki Updated on ・2 min read

📑 1. Theory
💻 2. Code
📝 3. Conclusion

The select statement

The select statement in Go looks like a switch
statement but for channels


  1. Each case inside a select holds a channel receive or send.
  2. Select waits until one case is ready and then runs it and its associated case statement.
  3. It chooses one at random if multiple channels are ready.
  4. It will block until one of the channels is ready.
  5. I think the select statement is one of the most important part of the Go concurrency model.

Please let me know if you notice any mistakes or I forgot something important 😅

Show me the code

Let's code a classical program that's generate a Multiplication Table.
Take a look at the main function:

type message struct {
    text   string
    number int
}

func main() {
    msg := make(chan message)
    exit := make(chan bool)

    go readInput(msg, exit)
    for {
        select {
        case m := <-msg:
            validateInputAndGetNumber(&m)
            printMultiplicationTable(m)
            fmt.Print("˲Give me a number or exit: ")
        case <-exit:
            fmt.Println("Exiting program...")
            os.Exit(1)
        }
    }
}
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  1. message struct is the type of channel that I use to communicate between goroutines. There are just two goroutines in this program, the execution of main function and the execution of readInput function and yes, the main function is executed as a goroutine by go runtime.
  2. Instantiate two channels: msg and exit I hope the variable name is self-explanatory😁 .
  3. go readInput(msg, exit) starts the goroutine to read the user input stdin data sending to the msg channel.
  4. for { select { ... } } it starts an infinite loop with the for keyword. This way we can keep listening to both channels with select forever.

Therefore the goroutine executed by go readInput(msg, exit) is sending data through the msg and exit channels, and the goroutine executed by main() is reading these channels and then when one of the channels is ready, that operation will proceed, and its corresponding statements.

The running code seems like this:

Alt Text

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Implementations of dev.to blog posts

Conclusion

My goal with this simple program is to demonstrate how we can use the select statement to handle incoming data from channels in a fancy way. I hope it could be helpful, especially for new Gophers 😄

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