strings: add Builder.cut_to (#10042)

vlib/builtin/rune.v

@@ -44,11 +44,6 @@ pub fn (b []byte) clone() []byte {
 
 // TODO remove this once runes are implemented
 pub fn (b []byte) bytestr() string {
-	return bytes2string(b)
-}
-
-// TODO copy pasted from builder.v
-fn bytes2string(b []byte) string {
 	unsafe {
 		buf := malloc(b.len + 1)
 		C.memcpy(buf, b.data, b.len)

vlib/strings/builder.v

@@ -72,28 +72,24 @@ pub fn (mut b Builder) go_back(n int) {
 	b.len -= n
 }
 
-fn bytes2string(b []byte) string {
-	mut copy := b.clone()
-	copy << byte(0)
-	return unsafe { tos(copy.data, copy.len - 1) }
-}
-
 // cut_last cuts the last `n` bytes from the buffer and returns them
 pub fn (mut b Builder) cut_last(n int) string {
-	res := bytes2string(b.buf[b.len - n..])
+	res := b.buf[b.len - n..].bytestr()
 	b.buf.trim(b.buf.len - n)
 	b.len -= n
 	return res
 }
 
-/*
+// cut_to cuts the string after `pos` and returns it.
+// if `pos` is superior to builder length, returns an empty string
+// and cancel further operations
 pub fn (mut b Builder) cut_to(pos int) string {
-	res := bytes2string( b.buf[pos..] )
-	b.buf.trim(pos)
-	b.len = pos
-	return res
+	if pos > b.len {
+		return ''
 	}
-*/
+	return b.cut_last(b.buf.len - pos)
+}
+
 // go_back_to resets the buffer to the given position `pos`
 // NB: pos should be < than the existing buffer length.
 pub fn (mut b Builder) go_back_to(pos int) {
@@ -119,7 +115,7 @@ pub fn (b &Builder) last_n(n int) string {
 	if n > b.len {
 		return ''
 	}
-	return bytes2string(b.buf[b.len - n..])
+	return b.buf[b.len - n..].bytestr()
 }
 
 // buf == 'hello world'
@@ -128,7 +124,7 @@ pub fn (b &Builder) after(n int) string {
 	if n >= b.len {
 		return ''
 	}
-	return bytes2string(b.buf[n..])
+	return b.buf[n..].bytestr()
 }
 
 // str returns a copy of all of the accumulated buffer content.

vlib/strings/builder_test.v

@@ -82,3 +82,15 @@ fn test_strings_builder_reuse() {
 	sb.write_string('hello')
 	assert sb.str() == 'hello'
 }
+
+fn test_cut_to() {
+	mut sb := strings.new_builder(16)
+	sb.write_string('hello')
+	assert sb.cut_to(3) == 'lo'
+	assert sb.len == 3
+	assert sb.cut_to(3) == ''
+	assert sb.len == 3
+	assert sb.cut_to(0) == 'hel'
+	assert sb.cut_to(32) == ''
+	assert sb.len == 0
+}