Go gotcha: Iteration variable doesn't see change in range loop

Why doesn't the iteration variable x notice that a[1] has been updated?

var a [2]int
for _, x := range a {
        fmt.Println("x =", x)
        a[1] = 8
}
fmt.Println("a =", a)
x = 0
x = 0        <- Why isn't this 8?
a = [0 8]
Answer

The range expression a is evaluated once before beginning the loop and a copy of the array is used to generate the iteration values.

To avoid copying the array, iterate over a slice instead:

var a [2]int
for _, x := range a[:] {
        fmt.Println("x =", x)
        a[1] = 8
}
fmt.Println("a =", a)

x = 0
x = 8
a = [0 8]

See Range loops (for each loops) explained for all about range loops in Go.

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