diff --git a/lib/std/collections/list.c3 b/lib/std/collections/list.c3
index c316999b9..05184c29c 100644
--- a/lib/std/collections/list.c3
+++ b/lib/std/collections/list.c3
@@ -151,7 +151,7 @@ fn void List.reserve(List* list, usz min_capacity)
 {
 	if (!min_capacity) return;
 	if (list.capacity >= min_capacity) return;
-	if (!list.allocator) list.allocator = mem::temp_allocator();
+	if (!list.allocator) list.allocator = mem::current_allocator();
 	min_capacity = math::next_power_of_2(min_capacity);
     list.entries = realloc_aligned(list.entries, Type.sizeof * min_capacity, .alignment = Type[1].alignof, .using = list.allocator) ?? null;
 	list.capacity = min_capacity;
diff --git a/lib/std/core/allocators/temp_allocator.c3 b/lib/std/core/allocators/temp_allocator.c3
index 81579b036..2bfe82970 100644
--- a/lib/std/core/allocators/temp_allocator.c3
+++ b/lib/std/core/allocators/temp_allocator.c3
@@ -154,8 +154,6 @@ fn void*! TempAllocator._realloc(TempAllocator* this, void* pointer, usz size, u
 		TempAllocatorPage *page = pointer - TempAllocatorPage.sizeof;
 		return this._realloc_page(page, size, alignment, offset);
 	}
-	assert(pointer < &this.data + this.capacity && pointer >= &this.data, "This is not a temp allocated pointer.");
-	assert(pointer < &this.data + this.used, "This is a stale temp pointer.");
 
 	// TODO optimize last allocation
 	TempAllocatorChunk* data = this._alloc(size, alignment, offset, size > chunk.size)?;
diff --git a/lib/std/core/dstring.c3 b/lib/std/core/dstring.c3
new file mode 100644
index 000000000..88771e1ac
--- /dev/null
+++ b/lib/std/core/dstring.c3
@@ -0,0 +1,368 @@
+module std::core::dstring;
+
+typedef DString = distinct void*;
+
+const usz MIN_CAPACITY @private = 16;
+
+fn DString new_with_capacity(usz capacity, Allocator* allocator = mem::current_allocator())
+{
+	if (capacity < MIN_CAPACITY) capacity = MIN_CAPACITY;
+	StringData* data = malloc(StringData, 1, .using = allocator, .end_padding = capacity);
+	data.allocator = allocator;
+	data.len = 0;
+	data.capacity = capacity;
+	return (DString)data;
+}
+
+fn DString tnew_with_capacity(usz capacity) => new_with_capacity(capacity, mem::temp_allocator()) @inline;
+
+fn DString new(String c = "", Allocator* allocator = mem::current_allocator())
+{
+	usz len = c.len;
+	StringData* data = (StringData*)new_with_capacity(len, allocator);
+	if (len)
+	{
+		data.len = len;
+		mem::copy(&data.chars, c.ptr, len);
+	}
+	return (DString)data;
+}
+
+fn DString tnew(String s = "") => new(s, mem::temp_allocator()) @inline;
+
+fn DString DString.new_concat(DString a, DString b, Allocator* allocator = mem::current_allocator())
+{
+	DString string = new_with_capacity(a.len() + b.len(), allocator);
+	string.append(a);
+	string.append(b);
+	return string;
+}
+
+fn DString DString.new_tconcat(DString a, DString b) => a.new_concat(b, mem::temp_allocator());
+
+fn ZString DString.zstr(DString str)
+{
+	StringData* data = str.data();
+	if (!data) return (ZString)"";
+	if (data.capacity == data.len)
+	{
+		str.reserve(1);
+		data.chars[data.len] = 0;
+	}
+	else if (data.chars[data.len] != 0)
+	{
+		data.chars[data.len] = 0;
+	}
+	return (ZString)&data.chars[0];
+}
+
+fn usz DString.capacity(DString this)
+{
+	if (!this) return 0;
+	return this.data().capacity;
+}
+
+fn usz DString.len(DString this)
+{
+	if (!this) return 0;
+	return this.data().len;
+}
+
+/**
+ * @require new_size <= this.len()
+ */
+fn void DString.chop(DString this, usz new_size)
+{
+	if (!this) return;
+	this.data().len = new_size;
+}
+
+fn String DString.str(DString str)
+{
+	StringData* data = (StringData*)str;
+	if (!data) return String {};
+	return (String)data.chars[:data.len];
+}
+
+fn void DString.append_utf32(DString* str, Char32[] chars)
+{
+	str.reserve(chars.len);
+	foreach (Char32 c : chars)
+	{
+		str.append_char32(c);
+	}
+}
+
+/**
+ * @require index < str.len()
+ **/
+fn void DString.set(DString str, usz index, char c)
+{
+	str.data().chars[index] = c;
+}
+
+fn void DString.append_repeat(DString* str, char c, usz times)
+{
+	if (times == 0) return;
+	str.reserve(times);
+	StringData* data = str.data();
+	for (usz i = 0; i < times; i++)
+	{
+        data.chars[data.len++] = c;
+	}
+}
+
+/**
+ * @require c <= 0x10ffff
+ */
+fn void DString.append_char32(DString* str, Char32 c)
+{
+	if (c < 0x7f)
+	{
+		str.reserve(1);
+		StringData* data = str.data();
+        data.chars[data.len++] = (char)c;
+        return;
+    }
+    if (c < 0x7ff)
+    {
+		str.reserve(2);
+		StringData* data = str.data();
+		data.chars[data.len++] = (char)(0xC0 | c >> 6);
+        data.chars[data.len++] = (char)(0x80 | (c & 0x3F));
+        return;
+    }
+    if (c < 0xffff)
+    {
+		str.reserve(3);
+		StringData* data = str.data();
+		data.chars[data.len++] = (char)(0xE0 | c >> 12);
+        data.chars[data.len++] = (char)(0x80 | (c >> 6 & 0x3F));
+        data.chars[data.len++] = (char)(0x80 | (c & 0x3F));
+        return;
+    }
+	str.reserve(4);
+	StringData* data = str.data();
+	data.chars[data.len++] = (char)(0xF0 | c >> 18);
+    data.chars[data.len++] = (char)(0x80 | (c >> 12 & 0x3F));
+    data.chars[data.len++] = (char)(0x80 | (c >> 6 & 0x3F));
+    data.chars[data.len++] = (char)(0x80 | (c & 0x3F));
+}
+
+fn DString DString.tcopy(DString* str) => str.copy(mem::temp_allocator());
+
+fn DString DString.copy(DString* str, Allocator* allocator = null)
+{
+	if (!str)
+	{
+		if (allocator) return new_with_capacity(0, allocator);
+		return (DString)null;
+	}
+	if (!allocator) allocator = mem::current_allocator();
+	StringData* data = str.data();
+	DString new_string = new_with_capacity(data.capacity, allocator);
+	mem::copy((char*)new_string.data(), (char*)data, StringData.sizeof + data.len);
+	return new_string;
+}
+
+fn ZString DString.copy_zstr(DString* str, Allocator* allocator = mem::current_allocator())
+{
+	usz str_len = str.len();
+	if (!str_len)
+	{
+		return (ZString)calloc(1, .using = allocator);
+	}
+	char* zstr = malloc(str_len + 1, .using = allocator);
+	StringData* data = str.data();
+	mem::copy(zstr, &data.chars, str_len);
+	zstr[str_len] = 0;
+	return (ZString)zstr;
+}
+
+fn String DString.copy_str(DString* str, Allocator* allocator = mem::current_allocator())
+{
+	return (String)str.copy_zstr(allocator)[:str.len()];
+}
+
+fn String DString.tcopy_str(DString* str) => str.copy_str(mem::temp_allocator()) @inline;
+
+fn bool DString.equals(DString str, DString other_string)
+{
+	StringData *str1 = str.data();
+	StringData *str2 = other_string.data();
+	if (str1 == str2) return true;
+	if (!str1) return str2.len == 0;
+	if (!str2) return str1.len == 0;
+	usz str1_len = str1.len;
+	if (str1_len != str2.len) return false;
+	for (int i = 0; i < str1_len; i++)
+	{
+		if (str1.chars[i] != str2.chars[i]) return false;
+	}
+	return true;
+}
+
+fn void DString.free(DString* str)
+{
+	if (!*str) return;
+	StringData* data = str.data();
+	if (!data) return;
+	free(data, .using = data.allocator);
+	*str = (DString)null;
+}
+
+fn bool DString.less(DString str, DString other_string)
+{
+	StringData* str1 = str.data();
+	StringData* str2 = other_string.data();
+	if (str1 == str2) return false;
+	if (!str1) return str2.len != 0;
+	if (!str2) return str1.len == 0;
+	usz str1_len = str1.len;
+	usz str2_len = str2.len;
+	if (str1_len != str2_len) return str1_len < str2_len;
+	for (int i = 0; i < str1_len; i++)
+	{
+		if (str1.chars[i] >= str2.chars[i]) return false;
+	}
+	return true;
+}
+
+fn void DString.append_chars(DString* this, String str)
+{
+	usz other_len = str.len;
+	if (!other_len) return;
+	if (!*this)
+	{
+		*this = new(str);
+		return;
+	}
+	this.reserve(other_len);
+	StringData* data = (StringData*)*this;
+	mem::copy(&data.chars[data.len], str.ptr, other_len);
+	data.len += other_len;
+}
+
+fn Char32[] DString.copy_utf32(DString* this, Allocator* allocator = mem::current_allocator())
+{
+	return str::utf8to32(this.str(), allocator) @inline!!;
+}
+
+fn void DString.append_string(DString* this, DString str)
+{
+	StringData* other = (StringData*)str;
+	if (!other) return;
+	this.append(str.str());
+}
+
+fn void DString.clear(DString* str)
+{
+	str.data().len = 0;
+}
+
+fn void DString.append_char(DString* str, char c)
+{
+	if (!*str)
+	{
+		*str = new_with_capacity(MIN_CAPACITY);
+	}
+	str.reserve(1);
+	StringData* data = (StringData*)*str;
+	data.chars[data.len++] = c;
+}
+
+
+macro void DString.append(DString* str, value)
+{
+	var $Type = $typeof(value);
+	$switch ($Type):
+		$case char:
+		$case ichar:
+			str.append_char(value);
+		$case DString:
+			str.append_string(value);
+		$case String:
+			str.append_chars(value);
+		$case Char32:
+			str.append_char32(value);
+		$default:
+			$if (@convertible(value, Char32)):
+				str.append_char32(value);
+			$elif (@convertible(value, String)):
+				str.append_chars(value);
+			$else:
+				$assert(false, "Unsupported type for append – use printf instead.");
+			$endif;
+	$endswitch;
+}
+
+
+fn usz! DString.printf(DString* str, String format, args...) @maydiscard
+{
+	Formatter formatter;
+	formatter.init(&out_string_append_fn, str);
+	return formatter.vprintf(format, args);
+}
+
+fn usz! DString.printfn(DString* str, String format, args...) @maydiscard
+{
+	Formatter formatter;
+	formatter.init(&out_string_append_fn, str);
+	usz len = formatter.vprintf(format, args)?;
+	str.append('\n');
+	return len + 1;
+}
+
+fn DString new_join(String[] s, String joiner, Allocator* allocator = mem::current_allocator())
+{
+	if (!s.len) return (DString)null;
+	usz total_size = joiner.len * s.len;
+	foreach (String* &str : s)
+	{
+		total_size += str.len;
+	}
+	DString res = new_with_capacity(total_size, allocator);
+	res.append(s[0]);
+	foreach (String* &str : s[1..])
+	{
+		res.append(joiner);
+		res.append(*str);
+	}
+	return res;
+}
+
+fn void! out_string_append_fn(char c, void* data) @private
+{
+	DynString* s = data;
+	s.append_char(c);
+}
+
+
+fn StringData* DString.data(DString str) @inline @private
+{
+	return (StringData*)str;
+}
+
+fn void DString.reserve(DString* str, usz addition) @private
+{
+	StringData* data = str.data();
+	if (!data)
+	{
+		*str = dstring::new_with_capacity(addition);
+		return;
+	}
+	usz len = data.len + addition;
+	if (data.capacity >= len) return;
+	usz new_capacity = data.capacity *= 2;
+	if (new_capacity < MIN_CAPACITY) new_capacity = MIN_CAPACITY;
+	*str = (DString)realloc(data, StringData.sizeof + new_capacity, .using = data.allocator);
+}
+
+
+struct StringData @private
+{
+	Allocator* allocator;
+	usz len;
+	usz capacity;
+	char[*] chars;
+}
diff --git a/lib/std/core/str.c3 b/lib/std/core/str.c3
index 63a37ff6b..d386d5338 100644
--- a/lib/std/core/str.c3
+++ b/lib/std/core/str.c3
@@ -22,6 +22,7 @@ fault NumberConversion
 	MALFORMED_FLOAT,
 	FLOAT_OUT_OF_RANGE,
 }
+
 fn VarString join(String[] s, String joiner)
 {
 	if (!s.len) return (VarString)null;
@@ -335,7 +336,7 @@ fn String! utf16to8(Char16[] utf16, Allocator* allocator = mem::current_allocato
 	return data[:len];
 }
 
-fn String copy(String s, Allocator* allocator = mem::current_allocator())
+	fn String copy(String s, Allocator* allocator = mem::current_allocator())
 {
     usz len = s.len;
     ZString str_copy = copy_zstring(s, allocator) @inline;
diff --git a/lib/std/core/string.c3 b/lib/std/core/string.c3
index a393161fe..a995c240d 100644
--- a/lib/std/core/string.c3
+++ b/lib/std/core/string.c3
@@ -4,7 +4,6 @@ import libc;
 typedef VarString = distinct void*;
 typedef DynStr = VarString;
 typedef DynString = VarString;
-typedef DString = VarString;
 typedef VString = VarString;
 typedef Text = VarString;
 
diff --git a/lib/std/io/io.c3 b/lib/std/io/io.c3
index 00951e431..140b78816 100644
--- a/lib/std/io/io.c3
+++ b/lib/std/io/io.c3
@@ -57,6 +57,8 @@ macro void print(x)
 		catch(stdout().print(x));
 	$case ZString:
 		catch(stdout().print(x.as_str()));
+	$case DString:
+		catch(stdout().print(x.str()));
 	$case VarString:
 		catch(stdout().print(x.str()));
 	$default:
@@ -76,6 +78,8 @@ macro void printn(x = "")
 		catch(stdout().printn(x));
 	$case ZString:
 		catch(stdout().printn(x.as_str()));
+	$case DString:
+		catch(stdout().printn(x.str()));
 	$case VarString:
 		catch(stdout().printn(x.str()));
 	$default:
diff --git a/lib/std/io/io_file.c3 b/lib/std/io/io_file.c3
index be8f77756..3010af629 100644
--- a/lib/std/io/io_file.c3
+++ b/lib/std/io/io_file.c3
@@ -131,9 +131,9 @@ fn usz! File.println(File file, String string) => file.printn(string);
  * @param [&in] file
  * @require file.file `File must be initialized`
  */
-fn VarString File.getline(File* file, Allocator* allocator = mem::current_allocator())
+fn DString File.getline(File* file, Allocator* allocator = mem::current_allocator())
 {
-	VarString s = string::new_with_capacity(120, allocator);
+	DString s = dstring::new_with_capacity(120, allocator);
 	while (!file.eof())
 	{
 		int c = libc::fgetc(file.file);
diff --git a/lib/std/io/io_printf.c3 b/lib/std/io/io_printf.c3
index 8e8f08be5..cb9492313 100644
--- a/lib/std/io/io_printf.c3
+++ b/lib/std/io/io_printf.c3
@@ -236,6 +236,10 @@ fn void! Formatter.out_str(Formatter* this, variant arg) @private
 			{
 				return this.out_substr(((VarString*)arg).str());
 			}
+			if (arg.type == DString.typeid)
+			{
+				return this.out_substr(((DString*)arg).str());
+			}
         	return this.out_str(variant { arg.ptr, arg.type.inner });
 		case POINTER:
 			if (this.print_with_function(arg)?) return;