strings: add Replacer, NewReplacer
This is just a new API to do many replacements at once.
While the point of this API is to be faster than doing replacements one
at a time, the implementation in this CL has the optimizations removed
and may actually be slower.
Future CLs will bring back & add optimizations.
R=r, rsc, rogpeppe
CC=golang-dev
https://golang.org/cl/5081042
diff --git a/src/pkg/strings/Makefile b/src/pkg/strings/Makefile
index c1be582..872bb43 100644
--- a/src/pkg/strings/Makefile
+++ b/src/pkg/strings/Makefile
@@ -7,6 +7,7 @@
TARG=strings
GOFILES=\
reader.go\
+ replace.go\
strings.go\
include ../../Make.pkg
diff --git a/src/pkg/strings/replace.go b/src/pkg/strings/replace.go
new file mode 100644
index 0000000..cf2c023
--- /dev/null
+++ b/src/pkg/strings/replace.go
@@ -0,0 +1,84 @@
+// Copyright 2011 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 strings
+
+import (
+ "io"
+ "os"
+)
+
+// Can't import ioutil for ioutil.Discard, due to ioutil/tempfile.go -> strconv -> strings
+var discard io.Writer = devNull(0)
+
+type devNull int
+
+func (devNull) Write(p []byte) (int, os.Error) {
+ return len(p), nil
+}
+
+type pair struct{ old, new string }
+
+// A Replacer replaces a list of strings with replacements.
+type Replacer struct {
+ p []pair
+}
+
+// NewReplacer returns a new Replacer from a list of old, new string pairs.
+// Replacements are performed in order, without overlapping matches.
+func NewReplacer(oldnew ...string) *Replacer {
+ if len(oldnew)%2 == 1 {
+ panic("strings.NewReplacer: odd argument count")
+ }
+ r := new(Replacer)
+ for len(oldnew) >= 2 {
+ r.p = append(r.p, pair{oldnew[0], oldnew[1]})
+ oldnew = oldnew[2:]
+ }
+ return r
+}
+
+type appendSliceWriter struct {
+ b []byte
+}
+
+func (w *appendSliceWriter) Write(p []byte) (int, os.Error) {
+ w.b = append(w.b, p...)
+ return len(p), nil
+}
+
+// Replace returns a copy of s with all replacements performed.
+func (r *Replacer) Replace(s string) string {
+ // TODO(bradfitz): optimized version
+ n, _ := r.WriteString(discard, s)
+ w := appendSliceWriter{make([]byte, 0, n)}
+ r.WriteString(&w, s)
+ return string(w.b)
+}
+
+// WriteString writes s to w with all replacements performed.
+func (r *Replacer) WriteString(w io.Writer, s string) (n int, err os.Error) {
+Input:
+ // TODO(bradfitz): optimized version
+ for i := 0; i < len(s); {
+ for _, p := range r.p {
+ if HasPrefix(s[i:], p.old) {
+ wn, err := w.Write([]byte(p.new))
+ n += wn
+ if err != nil {
+ return n, err
+ }
+ i += len(p.old)
+ continue Input
+ }
+ }
+ wn, err := w.Write([]byte{s[i]})
+ n += wn
+ if err != nil {
+ return n, err
+ }
+ i++
+ }
+ return n, nil
+}
diff --git a/src/pkg/strings/replace_test.go b/src/pkg/strings/replace_test.go
new file mode 100644
index 0000000..a7677a1
--- /dev/null
+++ b/src/pkg/strings/replace_test.go
@@ -0,0 +1,75 @@
+// Copyright 2009 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 strings_test
+
+import (
+ . "strings"
+ "testing"
+)
+
+type ReplacerTest struct {
+ m *Replacer
+ in string
+ out string
+}
+
+var htmlEscaper = NewReplacer("&", "&", "<", "<", ">", ">", "\"", """)
+
+// The http package's old HTML escaping function.
+func oldhtmlEscape(s string) string {
+ s = Replace(s, "&", "&", -1)
+ s = Replace(s, "<", "<", -1)
+ s = Replace(s, ">", ">", -1)
+ s = Replace(s, "\"", """, -1)
+ s = Replace(s, "'", "'", -1)
+ return s
+}
+
+var replacer = NewReplacer("aaa", "3[aaa]", "aa", "2[aa]", "a", "1[a]", "i", "i",
+ "longerst", "most long", "longer", "medium", "long", "short",
+ "X", "Y", "Y", "Z")
+
+var ReplacerTests = []ReplacerTest{
+ {htmlEscaper, "No changes", "No changes"},
+ {htmlEscaper, "I <3 escaping & stuff", "I <3 escaping & stuff"},
+ {htmlEscaper, "&&&", "&&&"},
+ {replacer, "fooaaabar", "foo3[aaa]b1[a]r"},
+ {replacer, "long, longerst, longer", "short, most long, medium"},
+ {replacer, "XiX", "YiY"},
+}
+
+func TestReplacer(t *testing.T) {
+ for i, tt := range ReplacerTests {
+ if s := tt.m.Replace(tt.in); s != tt.out {
+ t.Errorf("%d. Replace(%q) = %q, want %q", i, tt.in, s, tt.out)
+ }
+ }
+}
+
+var slowReplacer = NewReplacer("&&", "&", "<<", "<", ">>", ">", "\"\"", """, "''", "'")
+
+func BenchmarkReplacerSingleByte(b *testing.B) {
+ str := "I <3 benchmarking html & other stuff too >:D"
+ n := 0
+ for i := 0; i < b.N; i++ {
+ n += len(htmlEscaper.Replace(str))
+ }
+}
+
+func BenchmarkReplaceMap(b *testing.B) {
+ str := "I <<3 benchmarking html && other stuff too >>:D"
+ n := 0
+ for i := 0; i < b.N; i++ {
+ n += len(slowReplacer.Replace(str))
+ }
+}
+
+func BenchmarkOldHTTPHTMLReplace(b *testing.B) {
+ str := "I <3 benchmarking html & other stuff too >:D"
+ n := 0
+ for i := 0; i < b.N; i++ {
+ n += len(oldhtmlEscape(str))
+ }
+}
