Closured variables and the go statement

In this section, we are going to talk about closured variables, which are variables inside closures, and the go statement. Notice that closured variables in goroutines are evaluated when the goroutine actually runs and when the go statement is executed in order to create a new goroutine. This means that closured variables are going to be replaced by their values when the Go scheduler decides to execute the relevant code. This is illustrated in the main() function of goClosure.go:

func main() {
    for i := 0; i <= 20; i++ {
        go func() {
            fmt.Print(i, " ")
        }()
    }
    time.Sleep(time.Second)
    fmt.Println()
}

Running goClosure.go produces the following output:

$ go run goClosure.go 
3 7 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21 21

The program mostly prints the number 21, which is the last value of the variable of the for loop, and not the other numbers. As i is a closured...