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// Copyright 2012 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 main
import (
// Input holds an input string in both UTF-8 and UTF-16 format.
type Input struct {
index int // used for restoring to original random order
UTF8 []byte
UTF16 []uint16
key []byte // used for sorting
func (i Input) String() string {
return string(i.UTF8)
func makeInput(s8 []byte, s16 []uint16) Input {
return Input{UTF8: s8, UTF16: s16}
func makeInputString(s string) Input {
return Input{
UTF8: []byte(s),
UTF16: utf16.Encode([]rune(s)),
// Collator is an interface for architecture-specific implementations of collation.
type Collator interface {
// Key generates a sort key for the given input. Implemenations
// may return nil if a collator does not support sort keys.
Key(s Input) []byte
// Compare returns -1 if a < b, 1 if a > b and 0 if a == b.
Compare(a, b Input) int
// CollatorFactory creates a Collator for a given language tag.
type CollatorFactory struct {
name string
makeFn func(tag string) (Collator, error)
description string
var collators = []CollatorFactory{}
// AddFactory registers f as a factory for an implementation of Collator.
func AddFactory(f CollatorFactory) {
collators = append(collators, f)
func getCollator(name, locale string) Collator {
for _, f := range collators {
if == name {
col, err := f.makeFn(locale)
if err != nil {
return col
log.Fatalf("collator of type %q not found", name)
return nil
// goCollator is an implementation of Collator using go's own collator.
type goCollator struct {
c *collate.Collator
buf collate.Buffer
func init() {
AddFactory(CollatorFactory{"go", newGoCollator, "Go's native collator implementation."})
func newGoCollator(loc string) (Collator, error) {
c := &goCollator{c: collate.New(language.Make(loc))}
return c, nil
func (c *goCollator) Key(b Input) []byte {
return c.c.Key(&c.buf, b.UTF8)
func (c *goCollator) Compare(a, b Input) int {
return c.c.Compare(a.UTF8, b.UTF8)