Tour of Go 2.0

Select

Select is like a switch for channels. It lets a goroutine wait on multiple channel operations at once and act on whichever is ready first.

A select blocks until one of its cases can proceed. If multiple cases are ready at the same time, Go picks one at random — no priority, no starvation.

Try it: trace through the fibonacci example. The goroutine in main reads 10 values then sends on quit. The select inside fibonacci handles both the “produce a value” case and the “stop now” case cleanly — no polling, no flags.

main.go ▶ Run in Playground 
package main

import "fmt"

func fibonacci(c, quit chan int) {
	x, y := 0, 1
	for {
		select {
		case c <- x:
			x, y = y, x+y
		case <-quit:
			fmt.Println("quit")
			return
		}
	}
}

func main() {
	c := make(chan int)
	quit := make(chan int)
	go func() {
		for i := 0; i < 10; i++ {
			fmt.Println(<-c)
		}
		quit <- 0
	}()
	fibonacci(c, quit)
}