blob: bb2fffbc75b3a8be427b34682309b0347cbc6b5a [file] [log] [blame]
// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package stringset provides a way to represent a collection of strings
// compactly.
package stringset
import "sort"
// A Set holds a collection of strings that can be looked up by an index number.
type Set struct {
// These fields are exported to allow for code generation.
Data string
Index []uint16
// Elem returns the string with index i. It panics if i is out of range.
func (s *Set) Elem(i int) string {
return s.Data[s.Index[i]:s.Index[i+1]]
// Len returns the number of strings in the set.
func (s *Set) Len() int {
return len(s.Index) - 1
// Search returns the index of the given string or -1 if it is not in the set.
// The Set must have been created with strings in sorted order.
func Search(s *Set, str string) int {
// TODO: optimize this if it gets used a lot.
n := len(s.Index) - 1
p := sort.Search(n, func(i int) bool {
return s.Elem(i) >= str
if p == n || str != s.Elem(p) {
return -1
return p
// A Builder constructs Sets.
type Builder struct {
set Set
index map[string]int
// NewBuilder returns a new and initialized Builder.
func NewBuilder() *Builder {
return &Builder{
set: Set{
Index: []uint16{0},
index: map[string]int{},
// Set creates the set created so far.
func (b *Builder) Set() Set {
return b.set
// Index returns the index for the given string, which must have been added
// before.
func (b *Builder) Index(s string) int {
return b.index[s]
// Add adds a string to the index. Strings that are added by a single Add will
// be stored together, unless they match an existing string.
func (b *Builder) Add(ss ...string) {
// First check if the string already exists.
for _, s := range ss {
if _, ok := b.index[s]; ok {
b.index[s] = len(b.set.Index) - 1
b.set.Data += s
x := len(b.set.Data)
if x > 0xFFFF {
panic("Index too > 0xFFFF")
b.set.Index = append(b.set.Index, uint16(x))