A simple unsorted Set type for strings in Go (backed by a map).

main.go

package main

import (
	"fmt"
	"strings"
)

type StringSet map[string]struct{}

func (s *StringSet) String() string {
	return strings.Join(s.GetStrings(), " ")
}

func (s *StringSet) Add(value string) bool {
	_, found := (*s)[value]
	(*s)[value] = struct{}{}
	return !found
}

func (s *StringSet) Remove(value string) {
	delete(*s, value)
}

func (s *StringSet) GetStrings() (values []string) {
	values = make([]string, len(*s))
	i := 0
	for k := range *s {
		values[i] = k
		i++
	}
	return
}

func SlicesDifference(this, other []string) []string {
	sset := &StringSet{}
	for _, s := range append(this, other...) {
		sset.Add(s)
	}
	for _, s := range other {
		sset.Remove(s)
	}
	return sset.GetStrings()
}

func main() {
	sset := &StringSet{}
	sset.Add("a")
	sset.Add("b")
	sset.Add("a")
	sset.Add("c")

	fmt.Println(sset)
	fmt.Println(SlicesDifference([]string{"foo", "bar", "baz"}, []string{"baz", "quux"}))
}