Golang: Stable sort on priority and order

main.go

package main

import (
	"fmt"
	"sort"
)

// Item has a priority and an order
type Item struct {
	Prio  int
	Order int
}

// ByPrio is a slice of Item which implements the sort.Interface
type ByPrio []Item

// Len is i the sort.Interface
func (b ByPrio) Len() int {
	return len(b)
}

// Less is in the sort.Interface
func (b ByPrio) Less(i, j int) bool {
	// Higher prio comes first
	return b[i].Prio > b[j].Prio
}

// Swap is in the sort.Interface
func (b ByPrio) Swap(i, j int) {
	b[i], b[j] = b[j], b[i]
}

// Example
func main() {
	items := generateItems(10)
	fmt.Printf("\n    Unordered Items\n\n%v\n", stringify(items))

	sort.Stable(ByPrio(items))
	fmt.Printf("    Ordered Items\n\n%v\n", stringify(items))
}

func stringify(is []Item) (s string) {
	s += fmt.Sprintf(" Index | Order | Prio\n")
	s += fmt.Sprintf("-------+-------+------\n")
	for c, i := range is {
		s += fmt.Sprintf("%6d |%6d |%5d\n", c, i.Order, i.Prio)
	}
	return s
}

func generateItems(n int) []Item {
	ii := []Item{}
	for order := 0; order < n; order++ {
		prio := 0
		if order%3 == 0 {
			prio = 1 + order
		}
		ii = append(ii, Item{prio, order})
	}
	return ii
}