strings: added CutSpace, bytes: added CutSpace

src/bytes/bytes.go

@@ -1377,6 +1377,20 @@ func CutPrefix(s, prefix []byte) (after []byte, found bool) {
 	return s[len(prefix):], true
 }
 
+// CutSpace slices s around the each instance of one or more consecutive white space
+// characters, as defined by unicode.IsSpace, returning the text before and after the
+// white space characters. The found result reports white space characters appears in s.
+// If no whitespace characters appear in s, CutSpace returns s, nil, false.
+//
+// CutSpace returns slices of the original slice s, not copies.
+func CutSpace(s []byte) (before, after []byte, found bool) {
+	i := indexFunc(s, unicode.IsSpace, true)
+	if i == -1 {
+		return s, nil, false
+	}
+	return s[:i], TrimLeftFunc(s[i:], unicode.IsSpace), true
+}
+
 // CutSuffix returns s without the provided ending suffix byte slice
 // and reports whether it found the suffix.
 // If s doesn't end with suffix, CutSuffix returns s, false.

src/bytes/bytes_test.go

@@ -1758,6 +1758,30 @@ func TestCutPrefix(t *testing.T) {
 	}
 }
 
+var cutSpaceTests = []struct {
+	s             string
+	before, after string
+	found         bool
+}{
+	{"abc", "abc", "", false},
+	{" abc", "", "abc", true},
+	{"ab c", "ab", "c", true},
+	{"abc ", "abc", "", true},
+	{"abc   ", "abc", "", true},
+	{" abc   ", "", "abc   ", true},
+	{"a\u0085bc", "a", "bc", true},
+	{"a\t\n\v\f\r\u0085\u00A0bc", "a", "bc", true},
+	{"", "", "", false},
+}
+
+func TestCutSpace(t *testing.T) {
+	for _, tt := range cutSpaceTests {
+		if before, after, found := CutSpace([]byte(tt.s)); string(before) != tt.before || string(after) != tt.after || found != tt.found {
+			t.Errorf("Cut(%q) = %q, %q, %v, want %q, %q, %v", tt.s, before, after, found, tt.before, tt.after, tt.found)
+		}
+	}
+}
+
 var cutSuffixTests = []struct {
 	s, sep string
 	before string

src/strings/strings.go

@@ -1288,6 +1288,18 @@ func CutPrefix(s, prefix string) (after string, found bool) {
 	return s[len(prefix):], true
 }
 
+// CutSpace slices s around the each instance of one or more consecutive white space
+// characters, as defined by unicode.IsSpace, returning the text before and after the
+// white space characters. The found result reports white space characters appears in s.
+// If no whitespace characters appear in s, CutSpace returns s, "", false.
+func CutSpace(s string) (before, after string, found bool) {
+	i := indexFunc(s, unicode.IsSpace, true)
+	if i == -1 {
+		return s, "", false
+	}
+	return s[:i], TrimLeftFunc(s[i:], unicode.IsSpace), true
+}
+
 // CutSuffix returns s without the provided ending suffix string
 // and reports whether it found the suffix.
 // If s doesn't end with suffix, CutSuffix returns s, false.

src/strings/strings_test.go

@@ -1677,6 +1677,31 @@ func TestCutPrefix(t *testing.T) {
 	}
 }
 
+var cutSpaceTests = []struct {
+	s             string
+	before, after string
+	found         bool
+}{
+	{"abc", "abc", "", false},
+	{" abc", "", "abc", true},
+	{"ab c", "ab", "c", true},
+	{"abc ", "abc", "", true},
+	{"abc   ", "abc", "", true},
+	{" abc   ", "", "abc   ", true},
+	{"a\u0085bc", "a", "bc", true},
+	{"a\t\n\v\f\r\u0085\u00A0bc", "a", "bc", true},
+	{"", "", "", false},
+}
+
+func TestCutSpace(t *testing.T) {
+	for _, tt := range cutSpaceTests {
+		if before, after, found := CutSpace(tt.s); before != tt.before || after != tt.after || found != tt.found {
+			t.Errorf("CutSpace(%q) = %q, %q, %v, want %q, %q, %v", tt.s, before, after, found, tt.before, tt.after, tt.found)
+		}
+	}
+}
+
+
 var cutSuffixTests = []struct {
 	s, sep string
 	before string