Copy Method for Immutable slices and maps

immutable_collection.go

package main

import "fmt"

type nums []int

func (n nums) copy() []int {
	dest := make(nums, len(n))
	copy(dest, n)
	return dest
}

type codes map[string]int

func (c codes) copy() map[string]int {
	dest := make(codes)
	for k, v := range c {
		dest[k] = v
	}
	return dest
}

func main() {
	// slice
	x := nums{2, 5}
	fmt.Println(x)

	// try changing
	change(x.copy())

	// is changed?
	fmt.Println(x)
	
	// map
	y := make(codes)
	y["red"] = 1
	y["blue"] = 2
	fmt.Println(y)
	
	// try changing
	changeMap(y.copy())
	
	// is changed?
	fmt.Println(y)
}

func change(src []int) {
	src[0] = 3
	fmt.Println(src)
}

func changeMap(src map[string]int) {
	src["red"] = 3
	fmt.Println(src)
}