Select

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    In this tutorial, we will learn about the select statement in Go.

    The select statement blocks the code and waits for multiple channel operations simultaneously.

    A select blocks until one of its cases can run, then it executes that case. It chooses one at random if multiple are ready.

    package main
    
    import (
    	"fmt"
    	"time"
    )
    
    func main() {
    	one := make(chan string)
    	two := make(chan string)
    
    	go func() {
    		time.Sleep(time.Second * 2)
    		one <- "One"
    	}()
    
    	go func() {
    		time.Sleep(time.Second * 1)
    		two <- "Two"
    	}()
    
    	select {
    	case result := <-one:
    		fmt.Println("Received:", result)
    	case result := <-two:
    		fmt.Println("Received:", result)
    	}
    
    	close(one)
    	close(two)
    }
    

    Similar to switch , select also has a default case that runs if no other case is ready. This will help us send or receive without blocking.

    func main() {
    	one := make(chan string)
    	two := make(chan string)
    
    	for x := 0; x < 10; x++ {
    		go func() {
    			time.Sleep(time.Second * 2)
    			one <- "One"
    		}()
    
    		go func() {
    			time.Sleep(time.Second * 1)
    			two <- "Two"
    		}()
    	}
    
    	for x := 0; x < 10; x++ {
    		select {
    		case result := <-one:
    			fmt.Println("Received:", result)
    		case result := <-two:
    			fmt.Println("Received:", result)
    		default:
    			fmt.Println("Default...")
    			time.Sleep(200 * time.Millisecond)
    		}
    	}
    
    	close(one)
    	close(two)
    }
    

    It's also important to know that an empty select {} blocks forever.

    func main() {
    	...
    	select {}
    
    	close(one)
    	close(two)
    }
    
    © 2022 Karan Pratap Singh