strconv: add QuoteRune, which is analogous to Quote, but for runes rather than strings.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/4556059

src/pkg/strconv/quote.go

@@ -14,17 +14,14 @@ import (
 
 const lowerhex = "0123456789abcdef"
 
-// Quote returns a double-quoted Go string literal
-// representing s.  The returned string s uses Go escape
-// sequences (\t, \n, \xFF, \u0100) for control characters
-// and non-ASCII characters.
-func Quote(s string) string {
+func quoteWith(s string, quote byte) string {
 	var buf bytes.Buffer
-	buf.WriteByte('"')
+	buf.WriteByte(quote)
 	for ; len(s) > 0; s = s[1:] {
 		switch c := s[0]; {
-		case c == '"':
-			buf.WriteString(`\"`)
+		case c == quote:
+			buf.WriteByte('\\')
+			buf.WriteByte(quote)
 		case c == '\\':
 			buf.WriteString(`\\`)
 		case ' ' <= c && c <= '~':
@@ -69,8 +66,26 @@ func Quote(s string) string {
 			buf.WriteByte(lowerhex[c&0xF])
 		}
 	}
-	buf.WriteByte('"')
+	buf.WriteByte(quote)
 	return buf.String()
+
+}
+
+// Quote returns a double-quoted Go string literal
+// representing s.  The returned string uses Go escape
+// sequences (\t, \n, \xFF, \u0100) for control characters
+// and non-ASCII characters.
+func Quote(s string) string {
+	return quoteWith(s, '"')
+}
+
+// QuoteRune returns a single-quoted Go character literal
+// representing the rune.  The returned string uses Go escape
+// sequences (\t, \n, \xFF, \u0100) for control characters
+// and non-ASCII characters.
+func QuoteRune(rune int) string {
+	// TODO: avoid the allocation here.
+	return quoteWith(string(rune), '\'')
 }
 
 // CanBackquote returns whether the string s would be

src/pkg/strconv/quote_test.go

@@ -25,14 +25,37 @@ var quotetests = []quoteTest{
 }
 
 func TestQuote(t *testing.T) {
-	for i := 0; i < len(quotetests); i++ {
-		tt := quotetests[i]
+	for _, tt := range quotetests {
 		if out := Quote(tt.in); out != tt.out {
 			t.Errorf("Quote(%s) = %s, want %s", tt.in, out, tt.out)
 		}
 	}
 }
 
+type quoteRuneTest struct {
+	in  int
+	out string
+}
+
+var quoterunetests = []quoteRuneTest{
+	{'a', `'a'`},
+	{'\a', `'\a'`},
+	{'\\', `'\\'`},
+	{0xFF, `'\u00ff'`},
+	{0x263a, `'\u263a'`},
+	{0x0010ffff, `'\U0010ffff'`},
+	{0x0010ffff + 1, `'\ufffd'`},
+	{0x04, `'\x04'`},
+}
+
+func TestQuoteRune(t *testing.T) {
+	for _, tt := range quoterunetests {
+		if out := QuoteRune(tt.in); out != tt.out {
+			t.Errorf("QuoteRune(%U) = %s, want %s", tt.in, out, tt.out)
+		}
+	}
+}
+
 type canBackquoteTest struct {
 	in  string
 	out bool
@@ -80,8 +103,7 @@ var canbackquotetests = []canBackquoteTest{
 }
 
 func TestCanBackquote(t *testing.T) {
-	for i := 0; i < len(canbackquotetests); i++ {
-		tt := canbackquotetests[i]
+	for _, tt := range canbackquotetests {
 		if out := CanBackquote(tt.in); out != tt.out {
 			t.Errorf("CanBackquote(%q) = %v, want %v", tt.in, out, tt.out)
 		}
@@ -146,23 +168,20 @@ var misquoted = []string{
 }
 
 func TestUnquote(t *testing.T) {
-	for i := 0; i < len(unquotetests); i++ {
-		tt := unquotetests[i]
+	for _, tt := range unquotetests {
 		if out, err := Unquote(tt.in); err != nil && out != tt.out {
 			t.Errorf("Unquote(%#q) = %q, %v want %q, nil", tt.in, out, err, tt.out)
 		}
 	}
 
 	// run the quote tests too, backward
-	for i := 0; i < len(quotetests); i++ {
-		tt := quotetests[i]
+	for _, tt := range quotetests {
 		if in, err := Unquote(tt.out); in != tt.in {
 			t.Errorf("Unquote(%#q) = %q, %v, want %q, nil", tt.out, in, err, tt.in)
 		}
 	}
 
-	for i := 0; i < len(misquoted); i++ {
-		s := misquoted[i]
+	for _, s := range misquoted {
 		if out, err := Unquote(s); out != "" || err != os.EINVAL {
 			t.Errorf("Unquote(%#q) = %q, %v want %q, %v", s, out, err, "", os.EINVAL)
 		}