copy slice and append - used to build permutations

copy_slice_and_append.go

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package main

import "fmt"

type Item struct {
	name   string
	number int
}

func (it *Item) copy() *Item {
	return &Item{
		name:   it.name,
		number: it.number,
	}
}

func main() {
	names := []string{"a", "b"}
	numbers := []int{1, 2}

	items := []*Item{}

	for _, name := range names {
		item := &Item{name: name}
		items = append(items, item)
	}

	for n, i := range numbers {
		if n > 0 {
			fmt.Println(n, "make a copy of the items")
			itemCopies := make([]*Item, len(items))
			copy(itemCopies, items)

			for j := 0; j < len(items); j++ {
				itemCopies[j] = items[j].copy()
			}

			fmt.Println(n, "set the numbers on the copies")
			for _, item := range itemCopies {
				item.number = i
			}

			fmt.Println(n, "append the copies to the original")
			items = append(items, itemCopies...)
		} else {

			fmt.Println(n, "first pass set all the items to the first number")
			for _, item := range items {
				item.number = i
			}
		}
	}

	for n, i := range items {
		fmt.Printf("%d %+v\n", n, *i)
	}
}