bytes, strings: add Cut

Using Cut is a clearer way to write the vast majority (>70%) of existing code that calls Index, IndexByte, IndexRune, and SplitN. There is more discussion on https://golang.org/issue/46336. Fixes golang#46336. Change-Id: Ia418ed7c3706c65bf61e1b2c5baf534cb783e4d3 Reviewed-on: https://go-review.googlesource.com/c/go/+/351710 Trust: Russ Cox <rsc@golang.org> Run-TryBot: Russ Cox <rsc@golang.org> TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Ian Lance Taylor <iant@golang.org>
ydnar · Oct 6, 2021 · 8e36ab0 · 8e36ab0
1 parent 810b08b
commit 8e36ab0
Show file tree

Hide file tree

Showing 6 changed files with 178 additions and 90 deletions.
diff --git a/src/bytes/bytes.go b/src/bytes/bytes.go
@@ -1192,3 +1192,16 @@ func Index(s, sep []byte) int {
  }
  return -1
 }
+
+// Cut slices s around the first instance of sep,
+// returning the text before and after sep.
+// The found result reports whether sep appears in s.
+// If sep does not appear in s, cut returns s, "", false.
+//
+// Cut returns slices of the original slice s, not copies.
+func Cut(s, sep []byte) (before, after []byte, found bool) {
+ if i := Index(s, sep); i >= 0 {
+ return s[:i], s[i+len(sep):], true
+ }
+ return s, nil, false
+}
diff --git a/src/bytes/bytes_test.go b/src/bytes/bytes_test.go
@@ -1567,6 +1567,29 @@ func TestEqualFold(t *testing.T) {
  }
 }
 
+var cutTests = []struct {
+ s, sep string
+ before, after string
+ found bool
+}{
+ {"abc", "b", "a", "c", true},
+ {"abc", "a", "", "bc", true},
+ {"abc", "c", "ab", "", true},
+ {"abc", "abc", "", "", true},
+ {"abc", "", "", "abc", true},
+ {"abc", "d", "abc", "", false},
+ {"", "d", "", "", false},
+ {"", "", "", "", true},
+}
+
+func TestCut(t *testing.T) {
+ for _, tt := range cutTests {
+ if before, after, found := Cut([]byte(tt.s), []byte(tt.sep)); string(before) != tt.before || string(after) != tt.after || found != tt.found {
+ t.Errorf("Cut(%q, %q) = %q, %q, %v, want %q, %q, %v", tt.s, tt.sep, before, after, found, tt.before, tt.after, tt.found)
+ }
+ }
+}
+
 func TestBufferGrowNegative(t *testing.T) {
  defer func() {
  if err := recover(); err == nil {

diff --git a/src/bytes/example_test.go b/src/bytes/example_test.go
@@ -105,36 +105,6 @@ func ExampleCompare_search() {
  }
 }
 
-func ExampleTrimSuffix() {
- var b = []byte("Hello, goodbye, etc!")
- b = bytes.TrimSuffix(b, []byte("goodbye, etc!"))
- b = bytes.TrimSuffix(b, []byte("gopher"))
- b = append(b, bytes.TrimSuffix([]byte("world!"), []byte("x!"))...)
- os.Stdout.Write(b)
- // Output: Hello, world!
-}
-
-func ExampleTrimPrefix() {
- var b = []byte("Goodbye,, world!")
- b = bytes.TrimPrefix(b, []byte("Goodbye,"))
- b = bytes.TrimPrefix(b, []byte("See ya,"))
- fmt.Printf("Hello%s", b)
- // Output: Hello, world!
-}
-
-func ExampleFields() {
- fmt.Printf("Fields are: %q", bytes.Fields([]byte(" foo bar baz ")))
- // Output: Fields are: ["foo" "bar" "baz"]
-}
-
-func ExampleFieldsFunc() {
- f := func(c rune) bool {
- return !unicode.IsLetter(c) && !unicode.IsNumber(c)
- }
- fmt.Printf("Fields are: %q", bytes.FieldsFunc([]byte(" foo1;bar2,baz3..."), f))
- // Output: Fields are: ["foo1" "bar2" "baz3"]
-}
-
 func ExampleContains() {
  fmt.Println(bytes.Contains([]byte("seafood"), []byte("foo")))
  fmt.Println(bytes.Contains([]byte("seafood"), []byte("bar")))
@@ -181,6 +151,22 @@ func ExampleCount() {
  // 5
 }
 
+func ExampleCut() {
+ show := func(s, sep string) {
+ before, after, found := bytes.Cut([]byte(s), []byte(sep))
+ fmt.Printf("Cut(%q, %q) = %q, %q, %v\n", s, sep, before, after, found)
+ }
+ show("Gopher", "Go")
+ show("Gopher", "ph")
+ show("Gopher", "er")
+ show("Gopher", "Badger")
+ // Output:
+ // Cut("Gopher", "Go") = "", "pher", true
+ // Cut("Gopher", "ph") = "Go", "er", true
+ // Cut("Gopher", "er") = "Goph", "", true
+ // Cut("Gopher", "Badger") = "Gopher", "", false
+}
+
 func ExampleEqual() {
  fmt.Println(bytes.Equal([]byte("Go"), []byte("Go")))
  fmt.Println(bytes.Equal([]byte("Go"), []byte("C++")))
@@ -194,6 +180,19 @@ func ExampleEqualFold() {
  // Output: true
 }
 
+func ExampleFields() {
+ fmt.Printf("Fields are: %q", bytes.Fields([]byte(" foo bar baz ")))
+ // Output: Fields are: ["foo" "bar" "baz"]
+}
+
+func ExampleFieldsFunc() {
+ f := func(c rune) bool {
+ return !unicode.IsLetter(c) && !unicode.IsNumber(c)
+ }
+ fmt.Printf("Fields are: %q", bytes.FieldsFunc([]byte(" foo1;bar2,baz3..."), f))
+ // Output: Fields are: ["foo1" "bar2" "baz3"]
+}
+
 func ExampleHasPrefix() {
  fmt.Println(bytes.HasPrefix([]byte("Gopher"), []byte("Go")))
  fmt.Println(bytes.HasPrefix([]byte("Gopher"), []byte("C")))
@@ -259,6 +258,12 @@ func ExampleIndexRune() {
  // -1
 }
 
+func ExampleJoin() {
+ s := [][]byte{[]byte("foo"), []byte("bar"), []byte("baz")}
+ fmt.Printf("%s", bytes.Join(s, []byte(", ")))
+ // Output: foo, bar, baz
+}
+
 func ExampleLastIndex() {
  fmt.Println(bytes.Index([]byte("go gopher"), []byte("go")))
  fmt.Println(bytes.LastIndex([]byte("go gopher"), []byte("go")))
@@ -299,10 +304,12 @@ func ExampleLastIndexFunc() {
  // -1
 }
 
-func ExampleJoin() {
- s := [][]byte{[]byte("foo"), []byte("bar"), []byte("baz")}
- fmt.Printf("%s", bytes.Join(s, []byte(", ")))
- // Output: foo, bar, baz
+func ExampleReader_Len() {
+ fmt.Println(bytes.NewReader([]byte("Hi!")).Len())
+ fmt.Println(bytes.NewReader([]byte("こんにちは!")).Len())
+ // Output:
+ // 3
+ // 16
 }
 
 func ExampleRepeat() {
@@ -412,20 +419,6 @@ func ExampleTrimFunc() {
  // go-gopher!
 }
 
-func ExampleMap() {
- rot13 := func(r rune) rune {
- switch {
- case r >= 'A' && r <= 'Z':
- return 'A' + (r-'A'+13)%26
- case r >= 'a' && r <= 'z':
- return 'a' + (r-'a'+13)%26
- }
- return r
- }
- fmt.Printf("%s", bytes.Map(rot13, []byte("'Twas brillig and the slithy gopher...")))
- // Output: 'Gjnf oevyyvt naq gur fyvgul tbcure...
-}
-
 func ExampleTrimLeft() {
  fmt.Print(string(bytes.TrimLeft([]byte("453gopher8257"), "0123456789")))
  // Output:
@@ -442,11 +435,28 @@ func ExampleTrimLeftFunc() {
  // go-gopher!567
 }
 
+func ExampleTrimPrefix() {
+ var b = []byte("Goodbye,, world!")
+ b = bytes.TrimPrefix(b, []byte("Goodbye,"))
+ b = bytes.TrimPrefix(b, []byte("See ya,"))
+ fmt.Printf("Hello%s", b)
+ // Output: Hello, world!
+}
+
 func ExampleTrimSpace() {
  fmt.Printf("%s", bytes.TrimSpace([]byte(" \t\n a lone gopher \n\t\r\n")))
  // Output: a lone gopher
 }
 
+func ExampleTrimSuffix() {
+ var b = []byte("Hello, goodbye, etc!")
+ b = bytes.TrimSuffix(b, []byte("goodbye, etc!"))
+ b = bytes.TrimSuffix(b, []byte("gopher"))
+ b = append(b, bytes.TrimSuffix([]byte("world!"), []byte("x!"))...)
+ os.Stdout.Write(b)
+ // Output: Hello, world!
+}
+
 func ExampleTrimRight() {
  fmt.Print(string(bytes.TrimRight([]byte("453gopher8257"), "0123456789")))
  // Output:
@@ -463,21 +473,6 @@ func ExampleTrimRightFunc() {
  // 1234go-gopher!
 }
 
-func ExampleToUpper() {
- fmt.Printf("%s", bytes.ToUpper([]byte("Gopher")))
- // Output: GOPHER
-}
-
-func ExampleToUpperSpecial() {
- str := []byte("ahoj vývojári golang")
- totitle := bytes.ToUpperSpecial(unicode.AzeriCase, str)
- fmt.Println("Original : " + string(str))
- fmt.Println("ToUpper : " + string(totitle))
- // Output:
- // Original : ahoj vývojári golang
- // ToUpper : AHOJ VÝVOJÁRİ GOLANG
-}
-
 func ExampleToLower() {
  fmt.Printf("%s", bytes.ToLower([]byte("Gopher")))
  // Output: gopher
@@ -493,10 +488,17 @@ func ExampleToLowerSpecial() {
  // ToLower : ahoj vývojári golang
 }
 
-func ExampleReader_Len() {
- fmt.Println(bytes.NewReader([]byte("Hi!")).Len())
- fmt.Println(bytes.NewReader([]byte("こんにちは!")).Len())
+func ExampleToUpper() {
+ fmt.Printf("%s", bytes.ToUpper([]byte("Gopher")))
+ // Output: GOPHER
+}
+
+func ExampleToUpperSpecial() {
+ str := []byte("ahoj vývojári golang")
+ totitle := bytes.ToUpperSpecial(unicode.AzeriCase, str)
+ fmt.Println("Original : " + string(str))
+ fmt.Println("ToUpper : " + string(totitle))
  // Output:
- // 3
- // 16
+ // Original : ahoj vývojári golang
+ // ToUpper : AHOJ VÝVOJÁRİ GOLANG
 }
diff --git a/src/strings/example_test.go b/src/strings/example_test.go
@@ -10,17 +10,15 @@ import (
  "unicode"
 )
 
-func ExampleFields() {
- fmt.Printf("Fields are: %q", strings.Fields(" foo bar baz "))
- // Output: Fields are: ["foo" "bar" "baz"]
-}
-
-func ExampleFieldsFunc() {
- f := func(c rune) bool {
- return !unicode.IsLetter(c) && !unicode.IsNumber(c)
+func ExampleBuilder() {
+ var b strings.Builder
+ for i := 3; i >= 1; i-- {
+ fmt.Fprintf(&b, "%d...", i)
  }
- fmt.Printf("Fields are: %q", strings.FieldsFunc(" foo1;bar2,baz3...", f))
- // Output: Fields are: ["foo1" "bar2" "baz3"]
+ b.WriteString("ignition")
+ fmt.Println(b.String())
+
+ // Output: 3...2...1...ignition
 }
 
 func ExampleCompare() {
@@ -79,11 +77,40 @@ func ExampleCount() {
  // 5
 }
 
+func ExampleCut() {
+ show := func(s, sep string) {
+ before, after, found := strings.Cut(s, sep)
+ fmt.Printf("Cut(%q, %q) = %q, %q, %v\n", s, sep, before, after, found)
+ }
+ show("Gopher", "Go")
+ show("Gopher", "ph")
+ show("Gopher", "er")
+ show("Gopher", "Badger")
+ // Output:
+ // Cut("Gopher", "Go") = "", "pher", true
+ // Cut("Gopher", "ph") = "Go", "er", true
+ // Cut("Gopher", "er") = "Goph", "", true
+ // Cut("Gopher", "Badger") = "Gopher", "", false
+}
+
 func ExampleEqualFold() {
  fmt.Println(strings.EqualFold("Go", "go"))
  // Output: true
 }
 
+func ExampleFields() {
+ fmt.Printf("Fields are: %q", strings.Fields(" foo bar baz "))
+ // Output: Fields are: ["foo" "bar" "baz"]
+}
+
+func ExampleFieldsFunc() {
+ f := func(c rune) bool {
+ return !unicode.IsLetter(c) && !unicode.IsNumber(c)
+ }
+ fmt.Printf("Fields are: %q", strings.FieldsFunc(" foo1;bar2,baz3...", f))
+ // Output: Fields are: ["foo1" "bar2" "baz3"]
+}
+
 func ExampleHasPrefix() {
  fmt.Println(strings.HasPrefix("Gopher", "Go"))
  fmt.Println(strings.HasPrefix("Gopher", "C"))
@@ -370,14 +397,3 @@ func ExampleTrimRightFunc() {
  }))
  // Output: ¡¡¡Hello, Gophers
 }
-
-func ExampleBuilder() {
- var b strings.Builder
- for i := 3; i >= 1; i-- {
- fmt.Fprintf(&b, "%d...", i)
- }
- b.WriteString("ignition")
- fmt.Println(b.String())
-
- // Output: 3...2...1...ignition
-}
diff --git a/src/strings/strings.go b/src/strings/strings.go
@@ -1118,3 +1118,14 @@ func Index(s, substr string) int {
  }
  return -1
 }
+
+// Cut slices s around the first instance of sep,
+// returning the text before and after sep.
+// The found result reports whether sep appears in s.
+// If sep does not appear in s, cut returns s, "", false.
+func Cut(s, sep string) (before, after string, found bool) {
+ if i := Index(s, sep); i >= 0 {
+ return s[:i], s[i+len(sep):], true
+ }
+ return s, "", false
+}
diff --git a/src/strings/strings_test.go b/src/strings/strings_test.go
@@ -1579,7 +1579,30 @@ var CountTests = []struct {
 func TestCount(t *testing.T) {
  for _, tt := range CountTests {
  if num := Count(tt.s, tt.sep); num != tt.num {
- t.Errorf("Count(\"%s\", \"%s\") = %d, want %d", tt.s, tt.sep, num, tt.num)
+ t.Errorf("Count(%q, %q) = %d, want %d", tt.s, tt.sep, num, tt.num)
+ }
+ }
+}
+
+var cutTests = []struct {
+ s, sep string
+ before, after string
+ found bool
+}{
+ {"abc", "b", "a", "c", true},
+ {"abc", "a", "", "bc", true},
+ {"abc", "c", "ab", "", true},
+ {"abc", "abc", "", "", true},
+ {"abc", "", "", "abc", true},
+ {"abc", "d", "abc", "", false},
+ {"", "d", "", "", false},
+ {"", "", "", "", true},
+}
+
+func TestCut(t *testing.T) {
+ for _, tt := range cutTests {
+ if before, after, found := Cut(tt.s, tt.sep); before != tt.before || after != tt.after || found != tt.found {
+ t.Errorf("Cut(%q, %q) = %q, %q, %v, want %q, %q, %v", tt.s, tt.sep, before, after, found, tt.before, tt.after, tt.found)
  }
  }
 }