diff --git a/vlib/builtin/cfns.c.v b/vlib/builtin/cfns.c.v
index 82dd3292aa..7e5b06dc81 100644
--- a/vlib/builtin/cfns.c.v
+++ b/vlib/builtin/cfns.c.v
@@ -1,7 +1,7 @@
 module builtin
 
 // <string.h>
-fn C.memcpy(byteptr, byteptr, int) voidptr
+fn C.memcpy(dest byteptr, src byteptr, n int) voidptr
 
 fn C.memcmp(byteptr, byteptr, int) int
 
diff --git a/vlib/builtin/map.v b/vlib/builtin/map.v
index d2ca3e59fb..b962e8cbe6 100644
--- a/vlib/builtin/map.v
+++ b/vlib/builtin/map.v
@@ -94,107 +94,92 @@ fn fast_string_eq(a string, b string) bool {
 
 // Dynamic array with very low growth factor
 struct DenseArray {
+	key_bytes   int
 	value_bytes int
+	slot_bytes  int // sum of 2 fields above
 mut:
-	cap      u32
-	len      u32
-	deletes  u32
-	keys     &string
-	values   byteptr
+	cap      int
+	len      int
+	deletes  u32 // count
+	data     byteptr // array of interspersed key data and value data
 }
 
 [inline]
 [unsafe]
-fn new_dense_array(value_bytes int) DenseArray {
-	s8size := int(8 * sizeof(string))
+fn new_dense_array(key_bytes int, value_bytes int) DenseArray {
+	slot_bytes := key_bytes + value_bytes
+	cap := 8
 	return DenseArray{
+		key_bytes: key_bytes
 		value_bytes: value_bytes
-		cap: 8
+		slot_bytes: slot_bytes
+		cap: cap
 		len: 0
 		deletes: 0
-		keys: &string(malloc(s8size))
-		values: malloc(8 * value_bytes)
+		data: malloc(cap * slot_bytes) 
 	}
 }
 
 [inline]
 fn (d &DenseArray) key(i int) voidptr {
-	return unsafe {voidptr(d.keys + i)}
+	return unsafe {d.data + i * d.slot_bytes}
 }
 
 // for cgen
 [inline]
 fn (d &DenseArray) value(i int) voidptr {
-	return unsafe {voidptr(d.values + i * d.value_bytes)}
+	return unsafe {d.data + i * d.slot_bytes + d.key_bytes}
 }
 
 [inline]
 fn (d &DenseArray) has_index(i int) bool {
-	pkey := unsafe {d.keys + i}
+	// assume string keys for now
+	pkey := unsafe {&string(d.key(i))}
 	return pkey.str != 0
 }
 
 // Push element to array and return index
 // The growth-factor is roughly 1.125 `(x + (x >> 3))`
 [inline]
-fn (mut d DenseArray) push(key string, value voidptr) u32 {
+fn (mut d DenseArray) push(key voidptr, value voidptr) int {
 	if d.cap == d.len {
 		d.cap += d.cap >> 3
 		unsafe {
-			x := v_realloc(byteptr(d.keys), int(sizeof(string) * d.cap))
-			d.keys = &string(x)
-			d.values = v_realloc(byteptr(d.values), d.value_bytes * int(d.cap))
+			d.data = v_realloc(d.data, d.slot_bytes * d.cap)
 		}
 	}
 	push_index := d.len
 	unsafe {
-		d.keys[push_index] = key
-		C.memcpy(d.values + push_index * u32(d.value_bytes), value, d.value_bytes)
+		ptr := d.key(push_index)
+		C.memcpy(ptr, key, d.key_bytes)
+		C.memcpy(byteptr(ptr) + d.key_bytes, value, d.value_bytes)
 	}
 	d.len++
 	return push_index
 }
 
-fn (d DenseArray) get(i int) voidptr {
-	$if !no_bounds_checking? {
-		if i < 0 || i >= int(d.len) {
-			panic('DenseArray.get: index out of range (i == $i, d.len == $d.len)')
-		}
-	}
-	unsafe {
-		return byteptr(d.keys) + i * int(sizeof(string))
-	}
-}
-
 // Move all zeros to the end of the array and resize array
 fn (mut d DenseArray) zeros_to_end() {
-	mut tmp_value := malloc(d.value_bytes)
-	mut count := u32(0)
-	for i in 0 .. int(d.len) {
-		if unsafe {d.keys[i]}.str != 0 {
-			// swap keys
+	// TODO alloca?
+	mut tmp_buf := malloc(d.slot_bytes)
+	mut count := 0
+	for i in 0 .. d.len {
+		if d.has_index(i) {
+			// swap (TODO: optimize)
 			unsafe {
-				tmp_key := d.keys[count]
-				d.keys[count] = d.keys[i]
-				d.keys[i] = tmp_key
-			}
-			// swap values (TODO: optimize)
-			unsafe {
-				C.memcpy(tmp_value, d.values + count * u32(d.value_bytes), d.value_bytes)
-				C.memcpy(d.values + count * u32(d.value_bytes), d.values + i * d.value_bytes, d.value_bytes)
-				C.memcpy(d.values + i * d.value_bytes, tmp_value, d.value_bytes)
+				C.memcpy(tmp_buf, d.key(count), d.slot_bytes)
+				C.memcpy(d.key(count), d.key(i), d.slot_bytes)
+				C.memcpy(d.key(i), tmp_buf, d.slot_bytes)
 			}
 			count++
 		}
 	}
-	free(tmp_value)
+	free(tmp_buf)
 	d.deletes = 0
 	d.len = count
-	d.cap = if count < 8 { u32(8) } else { count }
+	d.cap = if count < 8 { 8 } else { count }
 	unsafe {
-		x := v_realloc(byteptr(d.keys), int(sizeof(string) * d.cap))
-		d.keys = &string(x)
-		d.values = v_realloc(byteptr(d.values), d.value_bytes * int(d.cap))
+		d.data = v_realloc(d.data, d.slot_bytes * d.cap)
 	}
 }
 
@@ -229,7 +214,7 @@ fn new_map_1(value_bytes int) map {
 		cap: init_cap
 		cached_hashbits: max_cached_hashbits
 		shift: init_log_capicity
-		key_values: new_dense_array(value_bytes)
+		key_values: new_dense_array(int(sizeof(string)), value_bytes)
 		metas: &u32(vcalloc(metasize))
 		extra_metas: extra_metas_inc
 		len: 0
@@ -324,10 +309,12 @@ fn (mut m map) set(k string, value voidptr) {
 	index,meta = m.meta_less(index, meta)
 	// While we might have a match
 	for meta == unsafe {m.metas[index]} {
-		kv_index := unsafe {m.metas[index + 1]}
-		if fast_string_eq(key, unsafe {m.key_values.keys[kv_index]}) {
+		kv_index := int(unsafe {m.metas[index + 1]})
+		pkey := unsafe {&string(m.key_values.key(kv_index))}
+		if fast_string_eq(key, *pkey) {
 			unsafe {
-				C.memcpy(m.key_values.values + kv_index * u32(m.value_bytes), value, m.value_bytes)
+				pval := pkey + 1 // skip string
+				C.memcpy(pval, value, m.value_bytes)
 			}
 			return
 		}
@@ -335,7 +322,7 @@ fn (mut m map) set(k string, value voidptr) {
 		meta += probe_inc
 	}
 	kv_index := m.key_values.push(key, value)
-	m.meta_greater(index, meta, kv_index)
+	m.meta_greater(index, meta, u32(kv_index))
 	m.len++
 }
 
@@ -367,13 +354,14 @@ fn (mut m map) rehash() {
 		m.metas = &u32(x)
 		C.memset(m.metas, 0, meta_bytes)
 	}
-	for i := u32(0); i < m.key_values.len; i++ {
-		if unsafe {m.key_values.keys[i]}.str == 0 {
+	for i := 0; i < m.key_values.len; i++ {
+		if !m.key_values.has_index(i) {
 			continue
 		}
-		mut index,mut meta := m.key_to_index(unsafe {m.key_values.keys[i]})
+		pkey := unsafe {&string(m.key_values.key(i))}
+		mut index,mut meta := m.key_to_index(*pkey)
 		index,meta = m.meta_less(index, meta)
-		m.meta_greater(index, meta, i)
+		m.meta_greater(index, meta, u32(i))
 	}
 }
 
@@ -403,18 +391,17 @@ fn (mut m map) cached_rehash(old_cap u32) {
 }
 
 // This method is used for assignment operators. If the argument-key
-// does not exist in the map, it's added to the map along with the zero/dafault value.
+// does not exist in the map, it's added to the map along with the zero/default value.
 // If the key exists, its respective value is returned.
 fn (mut m map) get_and_set(key string, zero voidptr) voidptr {
 	for {
 		mut index,mut meta := m.key_to_index(key)
 		for {
 			if meta == unsafe {m.metas[index]} {
-				kv_index := unsafe {m.metas[index + 1]}
-				if fast_string_eq(key, unsafe {m.key_values.keys[kv_index]}) {
-					unsafe {
-						return voidptr(m.key_values.values + kv_index * u32(m.value_bytes))
-					}
+				kv_index := int(unsafe {m.metas[index + 1]})
+				pkey := unsafe {&string(m.key_values.key(kv_index))}
+				if fast_string_eq(key, *pkey) {
+					return unsafe {byteptr(pkey) + m.key_values.key_bytes}
 				}
 			}
 			index += 2
@@ -435,11 +422,10 @@ fn (m map) get(key string, zero voidptr) voidptr {
 	mut index,mut meta := m.key_to_index(key)
 	for {
 		if meta == unsafe {m.metas[index]} {
-			kv_index := unsafe {m.metas[index + 1]}
-			if fast_string_eq(key, unsafe {m.key_values.keys[kv_index]}) {
-				unsafe {
-					return voidptr(m.key_values.values + kv_index * u32(m.value_bytes))
-				}
+			kv_index := int(unsafe {m.metas[index + 1]})
+			pkey := unsafe {&string(m.key_values.key(kv_index))}
+			if fast_string_eq(key, *pkey) {
+				return unsafe {byteptr(pkey) + m.key_values.key_bytes}
 			}
 		}
 		index += 2
@@ -454,9 +440,10 @@ fn (m map) exists(key string) bool {
 	mut index,mut meta := m.key_to_index(key)
 	for {
 		if meta == unsafe {m.metas[index]} {
-			kv_index := unsafe {m.metas[index + 1]}
-			if fast_string_eq(key, unsafe {m.key_values.keys[kv_index]}) {
-				return  true
+			kv_index := int(unsafe {m.metas[index + 1]})
+			pkey := unsafe {&string(m.key_values.key(kv_index))}
+			if fast_string_eq(key, *pkey) {
+				return true
 			}
 		}
 		index += 2
@@ -472,8 +459,9 @@ pub fn (mut m map) delete(key string) {
 	index,meta = m.meta_less(index, meta)
 	// Perform backwards shifting
 	for meta == unsafe {m.metas[index]} {
-		kv_index := unsafe {m.metas[index + 1]}
-		if fast_string_eq(key, unsafe {m.key_values.keys[kv_index]}) {
+		kv_index := int(unsafe {m.metas[index + 1]})
+		pkey := unsafe {&string(m.key_values.key(kv_index))}
+		if fast_string_eq(key, *pkey) {
 			for (unsafe {m.metas[index + 2]} >> hashbits) > 1 {
 				unsafe {
 					m.metas[index] = m.metas[index + 2] - probe_inc
@@ -488,8 +476,8 @@ pub fn (mut m map) delete(key string) {
 			m.key_values.deletes++
 			// Mark key as deleted
 			unsafe {
-				m.key_values.keys[kv_index].free()
-				C.memset(&m.key_values.keys[kv_index], 0, sizeof(string))
+				(*pkey).free()
+				C.memset(pkey, 0, sizeof(string))
 			}
 			if m.key_values.len <= 32 {
 				return
@@ -512,11 +500,12 @@ pub fn (mut m map) delete(key string) {
 pub fn (m &map) keys() []string {
 	mut keys := []string{ len:m.len }
 	mut j := 0
-	for i := u32(0); i < m.key_values.len; i++ {
-		if unsafe {m.key_values.keys[i]}.str == 0 {
+	for i := 0; i < m.key_values.len; i++ {
+		if !m.key_values.has_index(i) {
 			continue
 		}
-		keys[j] = unsafe {m.key_values.keys[i]}.clone()
+		pkey := unsafe {&string(m.key_values.key(i))}
+		keys[j] = pkey.clone()
 		j++
 	}
 	return keys
@@ -524,20 +513,16 @@ pub fn (m &map) keys() []string {
 
 [unsafe]
 pub fn (d DenseArray) clone() DenseArray {
-	ksize := int(d.cap * sizeof(string))
-	vsize := int(d.cap * u32(d.value_bytes))
 	res := DenseArray {
+		key_bytes:   d.key_bytes
 		value_bytes: d.value_bytes
+		slot_bytes:  d.slot_bytes
 		cap:         d.cap
 		len:         d.len
 		deletes:     d.deletes
-		keys:        unsafe {&string(malloc(ksize))}
-		values:      unsafe {byteptr(malloc(vsize))}
-	}
-	unsafe {
-		C.memcpy(res.keys, d.keys, ksize)
-		C.memcpy(res.values, d.values, vsize)
+		data:        unsafe {memdup(d.data, d.cap * d.slot_bytes)}
 	}
+	// FIXME clone each key
 	return res
 }
 
@@ -552,7 +537,7 @@ pub fn (m map) clone() map {
 		key_values:      unsafe {m.key_values.clone()}
 		metas:           &u32(malloc(metasize))
 		extra_metas:     m.extra_metas
-		len:            m.len
+		len:             m.len
 	}
 	unsafe {
 		C.memcpy(res.metas, m.metas, metasize)
@@ -565,17 +550,17 @@ pub fn (m &map) free() {
 	unsafe {
 		free(m.metas)
 	}
-	for i := u32(0); i < m.key_values.len; i++ {
-		if unsafe {m.key_values.keys[i]}.str == 0 {
+	for i := 0; i < m.key_values.len; i++ {
+		if !m.key_values.has_index(i) {
 			continue
 		}
 		unsafe {
-			m.key_values.keys[i].free()
+			pkey := &string(m.key_values.key(i))
+			(*pkey).free()
 		}
 	}
 	unsafe {
-		free(m.key_values.keys)
-		free(m.key_values.values)
+		free(m.key_values.data)
 	}
 }
 
diff --git a/vlib/v/gen/auto_str_methods.v b/vlib/v/gen/auto_str_methods.v
index 0481a6b0d9..5b2f7f3d99 100644
--- a/vlib/v/gen/auto_str_methods.v
+++ b/vlib/v/gen/auto_str_methods.v
@@ -264,7 +264,7 @@ fn (mut g Gen) gen_str_for_map(info table.Map, styp string, str_fn_name string)
 	g.auto_str_funcs.writeln('static string indent_${str_fn_name}($styp m, int indent_count) { /* gen_str_for_map */')
 	g.auto_str_funcs.writeln('\tstrings__Builder sb = strings__new_builder(m.key_values.len*10);')
 	g.auto_str_funcs.writeln('\tstrings__Builder_write(&sb, _SLIT("{"));')
-	g.auto_str_funcs.writeln('\tfor (unsigned int i = 0; i < m.key_values.len; ++i) {')
+	g.auto_str_funcs.writeln('\tfor (int i = 0; i < m.key_values.len; ++i) {')
 	g.auto_str_funcs.writeln('\t\tif (!DenseArray_has_index(&m.key_values, i)) { continue; }')
 	g.auto_str_funcs.writeln('\t\tstring key = *(string*)DenseArray_key(&m.key_values, i);')
 	g.auto_str_funcs.writeln('\t\tstrings__Builder_write(&sb, _STR("\'%.*s\\000\'", 2, key));')
diff --git a/vlib/v/gen/cgen.v b/vlib/v/gen/cgen.v
index 460946be2f..ff1163cba6 100644
--- a/vlib/v/gen/cgen.v
+++ b/vlib/v/gen/cgen.v
@@ -1233,7 +1233,7 @@ fn (mut g Gen) for_in(it ast.ForInStmt) {
 		g.write('$atmp_styp $atmp = ')
 		g.expr(it.cond)
 		g.writeln(';')
-		g.writeln('for (int $idx = 0; $idx < (int)${atmp}.key_values.len; ++$idx) {')
+		g.writeln('for (int $idx = 0; $idx < ${atmp}.key_values.len; ++$idx) {')
 		g.writeln('\tif (!DenseArray_has_index(&${atmp}.key_values, $idx)) {continue;}')
 		if it.key_var != '_' {
 			key_styp := g.typ(it.key_type)