bytes, strings: add new function Fields

R=rsc, r, phf
CC=golang-dev
https://golang.org/cl/170046

4 files changed, 132 insertions, 0 deletions

diff --git a/src/pkg/bytes/bytes.go b/src/pkg/bytes/bytes.go
index 0a21464133..d69af0136a 100644
--- a/src/pkg/bytes/bytes.go
+++ b/src/pkg/bytes/bytes.go
@@ -163,6 +163,44 @@ func SplitAfter(s, sep []byte, n int) [][]byte {
 	return genSplit(s, sep, len(sep), n)
 }
 
+// Fields splits the array s around each instance of one or more consecutive white space
+// characters, returning a slice of subarrays of s or an empty list if s contains only white space.
+func Fields(s []byte) [][]byte {
+	n := 0
+	inField := false
+	for i := 0; i < len(s); {
+		rune, size := utf8.DecodeRune(s[i:])
+		wasInField := inField
+		inField = !unicode.IsSpace(rune)
+		if inField && !wasInField {
+			n++
+		}
+		i += size
+	}
+
+	a := make([][]byte, n)
+	na := 0
+	fieldStart := -1
+	for i := 0; i <= len(s) && na < n; {
+		rune, size := utf8.DecodeRune(s[i:])
+		if fieldStart < 0 && size > 0 && !unicode.IsSpace(rune) {
+			fieldStart = i
+			i += size
+			continue
+		}
+		if fieldStart >= 0 && (size == 0 || unicode.IsSpace(rune)) {
+			a[na] = s[fieldStart:i]
+			na++
+			fieldStart = -1
+		}
+		if size == 0 {
+			break
+		}
+		i += size
+	}
+	return a[0:na]
+}
+
 // Join concatenates the elements of a to create a single byte array.   The separator
 // sep is placed between elements in the resulting array.
 func Join(a [][]byte, sep []byte) []byte {
diff --git a/src/pkg/bytes/bytes_test.go b/src/pkg/bytes/bytes_test.go
index 4c6d4166a0..28ec55e3a9 100644
--- a/src/pkg/bytes/bytes_test.go
+++ b/src/pkg/bytes/bytes_test.go
@@ -254,6 +254,36 @@ func TestSplitAfter(t *testing.T) {
 	}
 }
 
+type FieldsTest struct {
+	s string
+	a []string
+}
+
+var fieldstests = []FieldsTest{
+	FieldsTest{"", []string{}},
+	FieldsTest{" ", []string{}},
+	FieldsTest{" \t ", []string{}},
+	FieldsTest{"  abc  ", []string{"abc"}},
+	FieldsTest{"1 2 3 4", []string{"1", "2", "3", "4"}},
+	FieldsTest{"1  2  3  4", []string{"1", "2", "3", "4"}},
+	FieldsTest{"1\t\t2\t\t3\t4", []string{"1", "2", "3", "4"}},
+	FieldsTest{"1\u20002\u20013\u20024", []string{"1", "2", "3", "4"}},
+	FieldsTest{"\u2000\u2001\u2002", []string{}},
+	FieldsTest{"\n™\t™\n", []string{"™", "™"}},
+	FieldsTest{faces, []string{faces}},
+}
+
+func TestFields(t *testing.T) {
+	for _, tt := range fieldstests {
+		a := Fields(strings.Bytes(tt.s))
+		result := arrayOfString(a)
+		if !eq(result, tt.a) {
+			t.Errorf("Fields(%q) = %v; want %v", tt.s, a, tt.a)
+			continue
+		}
+	}
+}
+
 // Test case for any function which accepts and returns a byte array.
 // For ease of creation, we write the byte arrays as strings.
 type StringTest struct {
diff --git a/src/pkg/strings/strings.go b/src/pkg/strings/strings.go
index ae34a5f3c3..48d4f0e96a 100644
--- a/src/pkg/strings/strings.go
+++ b/src/pkg/strings/strings.go
@@ -134,6 +134,40 @@ func SplitAfter(s, sep string, n int) []string {
 	return genSplit(s, sep, len(sep), n)
 }
 
+// Fields splits the string s around each instance of one or more consecutive white space
+// characters, returning an array of substrings of s or an empty list if s contains only white space.
+func Fields(s string) []string {
+	n := 0
+	inField := false
+	for _, rune := range s {
+		wasInField := inField
+		inField = !unicode.IsSpace(rune)
+		if inField && !wasInField {
+			n++
+		}
+	}
+
+	a := make([]string, n)
+	na := 0
+	fieldStart := -1
+	for i, rune := range s {
+		if unicode.IsSpace(rune) {
+			if fieldStart >= 0 {
+				a[na] = s[fieldStart:i]
+				na++
+				fieldStart = -1
+			}
+		} else if fieldStart == -1 {
+			fieldStart = i
+		}
+	}
+	if fieldStart != -1 {
+		a[na] = s[fieldStart:]
+		na++
+	}
+	return a[0:na]
+}
+
 // Join concatenates the elements of a to create a single string.   The separator string
 // sep is placed between elements in the resulting string.
 func Join(a []string, sep string) string {
diff --git a/src/pkg/strings/strings_test.go b/src/pkg/strings/strings_test.go
index eb0f8d1fb5..05df55ca94 100644
--- a/src/pkg/strings/strings_test.go
+++ b/src/pkg/strings/strings_test.go
@@ -180,6 +180,36 @@ func TestSplitAfter(t *testing.T) {
 	}
 }
 
+type FieldsTest struct {
+	s string
+	a []string
+}
+
+var fieldstests = []FieldsTest{
+	FieldsTest{"", []string{}},
+	FieldsTest{" ", []string{}},
+	FieldsTest{" \t ", []string{}},
+	FieldsTest{"  abc  ", []string{"abc"}},
+	FieldsTest{"1 2 3 4", []string{"1", "2", "3", "4"}},
+	FieldsTest{"1  2  3  4", []string{"1", "2", "3", "4"}},
+	FieldsTest{"1\t\t2\t\t3\t4", []string{"1", "2", "3", "4"}},
+	FieldsTest{"1\u20002\u20013\u20024", []string{"1", "2", "3", "4"}},
+	FieldsTest{"\u2000\u2001\u2002", []string{}},
+	FieldsTest{"\n™\t™\n", []string{"™", "™"}},
+	FieldsTest{faces, []string{faces}},
+}
+
+func TestFields(t *testing.T) {
+	for _, tt := range fieldstests {
+		a := Fields(tt.s)
+		if !eq(a, tt.a) {
+			t.Errorf("Fields(%q) = %v; want %v", tt.s, a, tt.a)
+			continue
+		}
+	}
+}
+
+
 // Test case for any function which accepts and returns a single string.
 type StringTest struct {
 	in, out string