cursed_slice.go

// seen on r/rust making fun of Go

package main

import (
	"fmt"
)

func appendAndChange(numbers []int) {
	newNumbers := append(numbers, 24)
	newNumbers[0] = 576
	fmt.Println("\tinside function", newNumbers)
}

func main() {
	// for the 0,1,2 example it goes from 0,1,2 as input
	//      then 576,1,2,24 after but within appendAndChange as expected from appending 24 and changing first to 576
	//      then after comes back it is 0,1,2
	fmt.Println("0,1,2 example")
	slice := []int{0, 1, 2}
	fmt.Println("\tinside main before function", slice)
	appendAndChange(slice)
	fmt.Println("\tinside main after function", slice)
	// but when you append 3 it has different behavior from if you had entered []int{0,1,2,3}
	//      576,1,2,3,24 after but within appendAndChange as expected
	//      but gives 576,1,2,3 upon returning back to main
	//          which is neither the 0,1,2,3 you would expect if the appendAndChange only worked with a copy that has subsequently disappeared
	//          nor the 576,1,2,3,24 if it was the same as inside appendAndChange
	//      instead it mangles the effects of appendAndChange and the keeping the same length
	fmt.Println("0,1,2,3 example")
	slice = append(slice, 3)
	fmt.Println("\tinside main before function", slice)
	appendAndChange(slice)
	fmt.Println("\tinside main after function", slice)
}