strings: add Builder.write_rune/1 and Builder.write_runes/1 methods

vlib/builtin/rune.v

@@ -34,9 +34,7 @@ pub fn (c rune) str() string {
 [manualfree]
 pub fn (ra []rune) string() string {
 	mut sb := strings.new_builder(ra.len)
-	for r in ra {
-		sb.write_string(r.str())
-	}
+	sb.write_runes(ra)
 	res := sb.str()
 	unsafe { sb.free() }
 	return res

vlib/strings/builder.v

@@ -23,6 +23,29 @@ pub fn (mut b Builder) write_ptr(ptr &byte, len int) {
 	unsafe { b.push_many(ptr, len) }
 }
 
+// write_rune appends a single rune to the accumulated buffer
+[manualfree]
+pub fn (mut b Builder) write_rune(r rune) {
+	mut buffer := [5]byte{}
+	res := unsafe { utf32_to_str_no_malloc(u32(r), &buffer[0]) }
+	if res.len == 0 {
+		return
+	}
+	unsafe { b.push_many(res.str, res.len) }
+}
+
+// write_runes appends all the given runes to the accumulated buffer
+pub fn (mut b Builder) write_runes(runes []rune) {
+	mut buffer := [5]byte{}
+	for r in runes {
+		res := unsafe { utf32_to_str_no_malloc(u32(r), &buffer[0]) }
+		if res.len == 0 {
+			continue
+		}
+		unsafe { b.push_many(res.str, res.len) }
+	}
+}
+
 // write_b appends a single `data` byte to the accumulated buffer
 pub fn (mut b Builder) write_b(data byte) {
 	b << data

vlib/strings/builder_test.v

@@ -2,6 +2,8 @@ import strings
 
 type MyInt = int
 
+const maxn = 100000
+
 fn test_sb() {
 	mut sb := strings.new_builder(100)
 	sb.write_string('hi')
@@ -40,10 +42,6 @@ fn test_sb() {
 	//}
 }
 
-const (
-	maxn = 100000
-)
-
 fn test_big_sb() {
 	mut sb := strings.new_builder(100)
 	mut sb2 := strings.new_builder(10000)
@@ -94,3 +92,23 @@ fn test_cut_to() {
 	assert sb.cut_to(32) == ''
 	assert sb.len == 0
 }
+
+fn test_write_rune() {
+	mut sb := strings.new_builder(10)
+	sb.write_rune(`h`)
+	sb.write_rune(`e`)
+	sb.write_rune(`l`)
+	sb.write_rune(`l`)
+	sb.write_rune(`o`)
+	x := sb.str()
+	assert x == 'hello'
+}
+
+fn test_write_runes() {
+	mut sb := strings.new_builder(20)
+	sb.write_runes([`h`, `e`, `l`, `l`, `o`])
+	sb.write_rune(` `)
+	sb.write_runes([`w`, `o`, `r`, `l`, `d`])
+	x := sb.str()
+	assert x == 'hello world'
+}