diff --git a/sync/README.md b/sync/README.md
index 73a698f..49cf534 100644
--- a/sync/README.md
+++ b/sync/README.md
@@ -6,8 +6,6 @@ Additional synchronization primitives:
 
 **Thread-safe map**
 ```
-New() Map
-
 Map.Len() int
 Map.Get(key K) (V, bool)
 Map.Set(key K, value V)
@@ -26,8 +24,6 @@ Wait()
 
 **Singleflight**
 ```
-New() Group
-
 Group.Do(key K, fun func() V) V
 ```
 
diff --git a/sync/muxmap/map.go b/sync/hatmap/map.go
similarity index 88%
rename from sync/muxmap/map.go
rename to sync/hatmap/map.go
index 7520727..d82e6b3 100644
--- a/sync/muxmap/map.go
+++ b/sync/hatmap/map.go
@@ -1,4 +1,4 @@
-package muxmap
+package hatmap
 
 import "sync"
 
@@ -10,16 +10,9 @@ type Map[K comparable, V any] struct {
 	mu   sync.RWMutex // protects data
 }
 
-// New creates a new map. Optional parameter is a size hint.
-func New[K comparable, V any](size ...int) Map[K, V] {
-	switch len(size) {
-	case 0:
-		return Map[K, V]{data: make(map[K]V, 0)}
-	case 1:
-		return Map[K, V]{data: make(map[K]V, size[0])}
-	default:
-		panic("ambiguous map size")
-	}
+// New creates a new map with size hint.
+func New[K comparable, V any](size int) Map[K, V] {
+	return Map[K, V]{data: make(map[K]V, size)}
 }
 
 // Len returns the number of elements in the map.
@@ -33,6 +26,9 @@ func (m *Map[K, V]) Len() int {
 // Set sets the value by the given key.
 func (m *Map[K, V]) Set(key K, value V) {
 	m.mu.Lock()
+	if m.data == nil {
+		m.data = make(map[K]V)
+	}
 	m.data[key] = value
 	m.mu.Unlock()
 }
@@ -63,6 +59,9 @@ func (m *Map[K, V]) SetIf(key K, cond func(value V, exists bool) bool, valfunc f
 	}
 
 	value = valfunc(value)
+	if m.data == nil {
+		m.data = make(map[K]V)
+	}
 	m.data[key] = value
 	return value, true
 }
diff --git a/sync/muxmap/map_test.go b/sync/hatmap/map_test.go
similarity index 93%
rename from sync/muxmap/map_test.go
rename to sync/hatmap/map_test.go
index 26f553a..2fe74a6 100644
--- a/sync/muxmap/map_test.go
+++ b/sync/hatmap/map_test.go
@@ -1,17 +1,17 @@
-package muxmap_test
+package hatmap_test
 
 import (
 	"reflect"
 	"sync"
 	"testing"
 
-	"github.com/Zamony/go/sync/muxmap"
+	"github.com/Zamony/go/sync/hatmap"
 )
 
 func TestMapSetGet(t *testing.T) {
 	t.Parallel()
 
-	m := muxmap.New[string, int]()
+	var m hatmap.Map[string, int]
 	m.Set("a", 1)
 
 	value, ok := m.SetIf("b", func(value int, exists bool) bool {
@@ -59,7 +59,7 @@ func TestMapSetGet(t *testing.T) {
 func TestMapSetDelete(t *testing.T) {
 	t.Parallel()
 
-	m := muxmap.New[string, int]()
+	m := hatmap.New[string, int](3)
 	m.Set("a", 1)
 	m.Set("b", 2)
 	m.Set("c", 3)
@@ -86,7 +86,7 @@ func TestMapSetDelete(t *testing.T) {
 func TestMapForEach(t *testing.T) {
 	t.Parallel()
 
-	m := muxmap.New[string, int]()
+	var m hatmap.Map[string, int]
 	m.Set("a", 1)
 	m.Set("b", 2)
 	m.Set("c", 3)
@@ -111,7 +111,7 @@ func TestMapConcurrent(t *testing.T) {
 	t.Parallel()
 
 	const key = "a"
-	m := muxmap.New[string, int]()
+	var m hatmap.Map[string, int]
 	var wg sync.WaitGroup
 	defer wg.Wait()
 
diff --git a/sync/singleflight/singleflight.go b/sync/singleflight/singleflight.go
index 3b029a7..2b43090 100644
--- a/sync/singleflight/singleflight.go
+++ b/sync/singleflight/singleflight.go
@@ -3,7 +3,7 @@ package singleflight
 import (
 	"sync/atomic"
 
-	"github.com/Zamony/go/sync/muxmap"
+	"github.com/Zamony/go/sync/hatmap"
 )
 
 type result[T any] struct {
@@ -16,12 +16,7 @@ type result[T any] struct {
 //
 // Group must not be copied after first use.
 type Group[K comparable, V any] struct {
-	results muxmap.Map[K, *result[V]]
-}
-
-// New creates a new singleflight Group.
-func New[K comparable, V any]() Group[K, V] {
-	return Group[K, V]{muxmap.New[K, *result[V]]()}
+	results hatmap.Map[K, *result[V]]
 }
 
 // Do executes and returns the results of the given function, making
diff --git a/sync/singleflight/singleflight_test.go b/sync/singleflight/singleflight_test.go
index b340d12..4292860 100644
--- a/sync/singleflight/singleflight_test.go
+++ b/sync/singleflight/singleflight_test.go
@@ -15,7 +15,7 @@ func TestSingleFlight(t *testing.T) {
 	var ncalls int64
 	var wg sync.WaitGroup
 	defer wg.Wait()
-	single := singleflight.New[string, int64]()
+	single := singleflight.Group[string, int64]{}
 	for i := 0; i < 5; i++ {
 		wg.Add(1)
 		go func() {