slices.go

package main

import "fmt"

func inner(s []int) {
	s[len(s)-1] = 999
}

func inner2(s []int) {
	s[0] = 9
	s = append(s, 9999)
	s[1] = 99
	fmt.Println(s) // prints [9,99,999,9999], of course
}

func main() {
	s1 := []int{1, 2, 3}
	fmt.Println(s1) // prints [1,2,3], of course
	inner(s1)       // this changes the slice in-place
	fmt.Println(s1) // prints [1,2,999]
	inner2(s1)
	fmt.Println(s1) // prints 9, 2, 999 because s[0] was changed before appending
}

This is interesting: in Go, if you pass a slice into a function you can change the original slice inside the function -- if you don't expand the slice! As soon as you append() something to the slice, it creates a copy and now you are changing the copy, not the original!
(When reading "Learning Go" by Jon Bodner)