exp/locale/collate: added functionality for sorting.

Eliminates the need for the user to fiddle with keys.

R=rsc
CC=golang-dev
https://golang.org/cl/7060051

src/pkg/exp/locale/collate/sort.go

+// Copyright 2013 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 collate
+
+import (
+	"bytes"
+	"sort"
+)
+
+const (
+	maxSortBuffer  = 40960
+	maxSortEntries = 4096
+)
+
+type swapper interface {
+	Swap(i, j int)
+}
+
+type sorter struct {
+	buf  *Buffer
+	keys [][]byte
+	src  swapper
+}
+
+func (s *sorter) init(n int) {
+	if s.buf == nil {
+		s.buf = &Buffer{}
+		s.buf.init()
+	}
+	if cap(s.keys) < n {
+		s.keys = make([][]byte, n)
+	}
+	s.keys = s.keys[0:n]
+}
+
+func (s *sorter) clean() {
+	if len(s.buf.key) > maxSortBuffer {
+		s.buf.key = s.buf.buf[:0]
+	}
+	if len(s.keys) > maxSortEntries {
+		s.keys = nil
+	}
+}
+
+func (s *sorter) sort(src swapper) {
+	s.src = src
+	sort.Sort(s)
+}
+
+func (s sorter) Len() int {
+	return len(s.keys)
+}
+
+func (s sorter) Less(i, j int) bool {
+	return bytes.Compare(s.keys[i], s.keys[j]) == -1
+}
+
+func (s sorter) Swap(i, j int) {
+	s.keys[i], s.keys[j] = s.keys[j], s.keys[i]
+	s.src.Swap(i, j)
+}
+
+// A Lister can be sorted by Collator's Sort method.
+type Lister interface {
+	Len() int
+	Swap(i, j int)
+	// Bytes returns the bytes of the text at index i.
+	Bytes(i int) []byte
+}
+
+// Sort uses sort.Sort to sort the strings represented by x using the rules of c.
+func (c *Collator) Sort(x Lister) {
+	n := x.Len()
+	c.sorter.init(n)
+	for i := 0; i < n; i++ {
+		c.sorter.keys[i] = c.Key(c.sorter.buf, x.Bytes(i))
+	}
+	c.sorter.sort(x)
+}
+
+// Strings sorts x using the rules of c.
+func (c *Collator) Strings(x []string) {
+	c.sorter.init(len(x))
+	for i, s := range x {
+		c.sorter.keys[i] = c.KeyFromString(c.sorter.buf, s)
+	}
+	c.sorter.sort(sort.StringSlice(x))
+}

src/pkg/exp/locale/collate/sort_test.go

+// Copyright 2013 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 collate_test
+
+import (
+	"exp/locale/collate"
+	"fmt"
+	"testing"
+)
+
+func ExampleCollator_Strings() {
+	c := collate.New("root")
+	strings := []string{
+		"ad",
+		"äb",
+		"ac",
+	}
+	c.Strings(strings)
+	fmt.Println(strings)
+	// Output: [äb ac ad]
+}
+
+type sorter []string
+
+func (s sorter) Len() int {
+	return len(s)
+}
+
+func (s sorter) Swap(i, j int) {
+	s[j], s[i] = s[i], s[j]
+}
+
+func (s sorter) Bytes(i int) []byte {
+	return []byte(s[i])
+}
+
+func TestSort(t *testing.T) {
+	c := collate.New("en")
+	strings := []string{
+		"bcd",
+		"abc",
+		"ddd",
+	}
+	c.Sort(sorter(strings))
+	res := fmt.Sprint(strings)
+	want := "[abc bcd ddd]"
+	if res != want {
+		t.Errorf("found %s; want %s", res, want)
+	}
+}