diff --git a/compiler/fn.v b/compiler/fn.v
index 9bcf77c1e8..75104e9165 100644
--- a/compiler/fn.v
+++ b/compiler/fn.v
@@ -4,6 +4,8 @@
 
 module main
 
+import strings 
+
 const (
 	MaxLocalVars = 50
 )
@@ -809,7 +811,7 @@ fn contains_capital(s string) bool {
 
 // "fn (int, string) int"
 fn (f Fn) typ_str() string {
-	mut sb := new_string_builder(50)
+	mut sb := strings.new_builder(50)
 	sb.write('fn (')
 	for i, arg in f.args {
 		sb.write(arg.typ)
diff --git a/compiler/main.v b/compiler/main.v
index 14001137fe..5d6994d329 100644
--- a/compiler/main.v
+++ b/compiler/main.v
@@ -91,6 +91,7 @@ mut:
 	show_c_cmd     bool // `v -show_c_cmd` prints the C command to build program.v.c
 	sanitize       bool // use Clang's new "-fsanitize" option
 	is_debug       bool // keep compiled C files
+	no_auto_free   bool // `v -nofree` disable automatic `free()` insertion for better performance in some applications  (e.g. compilers) 
 }
 
 
@@ -290,7 +291,7 @@ void init_consts();')
 	}
 	v.log('Done parsing.')
 	// Write everything
-	mut d := new_string_builder(10000)// Just to avoid some unnecessary allocations
+	mut d := strings.new_builder(10000)// Just to avoid some unnecessary allocations
 	d.writeln(cgen.includes.join_lines())
 	d.writeln(cgen.typedefs.join_lines())
 	d.writeln(cgen.types.join_lines())
@@ -872,7 +873,6 @@ fn new_v(args[]string) *V {
 	'utf8.v',
 	'map.v',
 	'option.v',
-	'string_builder.v',
 	]
 	// Location of all vlib files
 	mut lang_dir := ''
diff --git a/compiler/parser.v b/compiler/parser.v
index 90a4700b30..90d835c78b 100644
--- a/compiler/parser.v
+++ b/compiler/parser.v
@@ -839,7 +839,7 @@ fn (p mut Parser) get_type() string {
 		p.error('unknown type `$typ`')
 	}
 	if mul {
-		typ += repeat_char(`*`, nr_muls)
+		typ += strings.repeat(`*`, nr_muls)
 	}
 	// Register an []array type
 	if is_arr2 {
@@ -3175,7 +3175,7 @@ fn (p &Parser) building_v() bool {
 // fmt helpers
 fn (scanner mut Scanner) fgen(s string) {
 	if scanner.fmt_line_empty {
-		s = repeat_char(`\t`, scanner.fmt_indent) + s
+		s = strings.repeat(`\t`, scanner.fmt_indent) + s
 	}
 	scanner.fmt_out.write(s)
 	scanner.fmt_line_empty = false
@@ -3183,7 +3183,7 @@ fn (scanner mut Scanner) fgen(s string) {
 
 fn (scanner mut Scanner) fgenln(s string) {
 	if scanner.fmt_line_empty {
-		s = repeat_char(`\t`, scanner.fmt_indent) + s
+		s = strings.repeat(`\t`, scanner.fmt_indent) + s
 	}
 	scanner.fmt_out.writeln(s)
 	scanner.fmt_line_empty = true
diff --git a/compiler/scanner.v b/compiler/scanner.v
index 527db200b9..0e2e183438 100644
--- a/compiler/scanner.v
+++ b/compiler/scanner.v
@@ -18,7 +18,7 @@ mut:
 	started        bool
 	is_fmt         bool
 	// vfmt fields
-	fmt_out        StringBuilder
+	fmt_out        strings.Builder
 	fmt_indent     int
 	fmt_line_empty bool
 }
@@ -40,7 +40,7 @@ fn new_scanner(file_path string) *Scanner {
 	scanner := &Scanner {
 		file_path: file_path
 		text: text
-		fmt_out: new_string_builder(1000)
+		fmt_out: strings.new_builder(1000)
 	}
 	// println('new scanner "$file_path" txt.len=$scanner.text.len')
 	return scanner
diff --git a/vlib/builtin/array.v b/vlib/builtin/array.v
index 4936480d3e..0848addcf4 100644
--- a/vlib/builtin/array.v
+++ b/vlib/builtin/array.v
@@ -25,6 +25,12 @@ fn new_array(mylen, cap, elm_size int) array {
 	return arr
 }
 
+
+// TODO 
+pub fn _make(len, cap, elm_size int) array {
+	return new_array(len, cap, elm_size) 
+} 
+
 // Private function, used by V (`nums := [1, 2, 3]`)
 fn new_array_from_c_array(len, cap, elm_size int, c_array voidptr) array {
 	arr := array {
diff --git a/vlib/builtin/string.v b/vlib/builtin/string.v
index 0086930933..eade49afe7 100644
--- a/vlib/builtin/string.v
+++ b/vlib/builtin/string.v
@@ -795,18 +795,6 @@ pub fn (c byte) is_white() bool {
 	return i == 10 || i == 32 || i == 9 || i == 13 || c == `\r`
 }
 
-// TODO move this to strings.repeat()
-pub fn repeat_char(c byte, n int) string {
-	if n <= 0 {
-		return ''
-	}
-	mut arr := malloc(n + 1)
-	for i := 0; i < n; i++ {
-		arr[i] = c
-	}
-	arr[n] = `\0`
-	return tos(arr, n)
-}
 
 pub fn (s string) hash() int {
 	mut hash := int(0)
diff --git a/vlib/builtin/string_builder.v b/vlib/strings/builder.v
similarity index 50%
rename from vlib/builtin/string_builder.v
rename to vlib/strings/builder.v
index 9660cb45aa..4cc0e8a7e7 100644
--- a/vlib/builtin/string_builder.v
+++ b/vlib/strings/builder.v
@@ -2,38 +2,39 @@
 // Use of this source code is governed by an MIT license
 // that can be found in the LICENSE file.
 
-module builtin
+module strings 
 
-struct StringBuilder {
+struct Builder {
+mut: 
 	buf []byte
 	len int
 }
 
-pub fn new_string_builder(initial_size int) StringBuilder {
-	return StringBuilder {
-		buf: new_array(0, initial_size, sizeof(byte))
+pub fn new_builder(initial_size int) Builder {
+	return Builder {
+		buf: _make(0, initial_size, sizeof(byte))
 	}
 }
 
-pub fn (b mut StringBuilder) write(s string) {
+pub fn (b mut Builder) write(s string) {
 	b.buf._push_many(s.str, s.len)
 	b.len += s.len
 }
 
-pub fn (b mut StringBuilder) writeln(s string) {
+pub fn (b mut Builder) writeln(s string) {
 	b.buf._push_many(s.str, s.len)
 	b.buf << `\n`
 	b.len += s.len + 1
 }
 
-pub fn (b StringBuilder) str() string {
+pub fn (b Builder) str() string {
 	return tos(b.buf.data, b.len)
 }
 
-pub fn (b StringBuilder) cut(n int) {
+pub fn (b Builder) cut(n int) {
 	b.len -= n
 }
 
-pub fn (b mut StringBuilder) free() {
+pub fn (b mut Builder) free() {
 	C.free(b.buf.data)
 }
diff --git a/vlib/strings/builder_test.v b/vlib/strings/builder_test.v
new file mode 100644
index 0000000000..8831ce990c
--- /dev/null
+++ b/vlib/strings/builder_test.v
@@ -0,0 +1,15 @@
+import strings
+ 
+fn test_sb() {
+	mut sb := strings.Builder{}
+	sb.write('hi')
+	sb.write('!')
+	sb.write('hello')
+	assert sb.str() == 'hi!hello'
+	sb = strings.new_builder(10)
+	sb.write('a')
+	sb.write('b')
+	println(sb.str())
+	assert sb.str() == 'ab'
+}
+
diff --git a/vlib/strings/strings.v b/vlib/strings/strings.v
new file mode 100644
index 0000000000..ce32c38aa9
--- /dev/null
+++ b/vlib/strings/strings.v
@@ -0,0 +1,13 @@
+module strings 
+
+pub fn repeat(c byte, n int) string {
+	if n <= 0 {
+		return ''
+	}
+	mut arr := malloc(n + 1)
+	for i := 0; i < n; i++ {
+		arr[i] = c
+	}
+	arr[n] = `\0`
+	return tos(arr, n)
+}
diff --git a/vlib/strings/strings_test.v b/vlib/strings/strings_test.v
new file mode 100644
index 0000000000..2f87855181
--- /dev/null
+++ b/vlib/strings/strings_test.v
@@ -0,0 +1,6 @@
+import strings
+
+fn test_repeat() {
+	assert strings.repeat(`x`, 10) == 'xxxxxxxxxx' 
+	assert strings.repeat(`a`, 1) == 'a' 
+}