diff --git a/clock/Clock_test.go b/clock/Clock_test.go
index 9d57bb8..7182b75 100644
--- a/clock/Clock_test.go
+++ b/clock/Clock_test.go
@@ -59,7 +59,7 @@ func TestNow(t *testing.T) {
 			expTime := let.Time(s)
 
 			s.Before(func(t *testcase.T) {
-				timecop.Travel(t, expTime.Get(t).UTC(), timecop.Freeze())
+				timecop.Travel(t, expTime.Get(t).UTC(), timecop.Freeze)
 			})
 
 			s.Then("the time it just returned in the same Local as time.Now()", func(t *testcase.T) {
@@ -230,7 +230,7 @@ func TestAfter(t *testing.T) {
 
 	s.Test("no matter what, when the wait time is zero, clock.After returns instantly", func(t *testcase.T) {
 		timecop.SetSpeed(t, 0.001)
-		timecop.Travel(t, time.Second, timecop.Freeze())
+		timecop.Travel(t, time.Second, timecop.Freeze)
 		assert.Within(t, time.Millisecond, func(ctx context.Context) {
 			<-clock.After(0)
 		}, "expected to finish instantly")
diff --git a/clock/README.md b/clock/README.md
index ef1ab84..4cf8a23 100644
--- a/clock/README.md
+++ b/clock/README.md
@@ -63,7 +63,7 @@ func Test(t *testing.T) {
       CreatedAt: clock.TimeNow(),
    }
 
-   timecop.Travel(t, expected.CreatedAt, timecop.Freeze())
+   timecop.Travel(t, expected.CreatedAt, timecop.Freeze)
 
    assert.Equal(t, expected, MyFunc())
 }
diff --git a/clock/examples_test.go b/clock/examples_test.go
index 71159bf..caa1635 100644
--- a/clock/examples_test.go
+++ b/clock/examples_test.go
@@ -26,7 +26,7 @@ func ExampleTimeNow_freeze() {
 		CreatedAt: clock.Now(),
 	}
 
-	timecop.Travel(tb, expected.CreatedAt, timecop.Freeze())
+	timecop.Travel(tb, expected.CreatedAt, timecop.Freeze)
 
 	assert.Equal(tb, expected, MyFunc())
 }
@@ -43,7 +43,7 @@ func ExampleTimeNow_withTravelByDate() {
 	var tb testing.TB
 
 	date := time.Date(2022, 01, 01, 12, 0, 0, 0, time.Local)
-	timecop.Travel(tb, date, timecop.Freeze()) // freeze the time until it is read
+	timecop.Travel(tb, date, timecop.Freeze) // freeze the time until it is read
 	time.Sleep(time.Second)
 	_ = clock.Now() // equals with date
 }
diff --git a/clock/timecop/timecop.go b/clock/timecop/timecop.go
index 70e943f..de7599d 100644
--- a/clock/timecop/timecop.go
+++ b/clock/timecop/timecop.go
@@ -48,16 +48,20 @@ func travelByTime(tb testing.TB, target time.Time, opt internal.Option) {
 	tb.Cleanup(internal.SetTime(target, opt))
 }
 
-// Freeze instruct travel to freeze the time.
-func Freeze() TravelOption {
-	return fnTravelOption(func(o *internal.Option) {
-		o.Freeze = true
-	})
+// Freeze is a Travel TravelOption, and it instruct travel to freeze the time wherever it lands after the travelling..
+const Freeze = freeze(0)
+
+type freeze int
+
+func (freeze) configure(o *internal.Option) {
+	o.Freeze = true
 }
 
-// Unfreeze instruct travel to unfreeze the time.
-func Unfreeze() TravelOption {
-	return fnTravelOption(func(o *internal.Option) {
-		o.Unfreeze = true
-	})
+// Unfreeze is a Travel TravelOption, and it instruct travel that after the time travelling, the flow of time should continue.
+const Unfreeze = unfreeze(0)
+
+type unfreeze int
+
+func (unfreeze) configure(o *internal.Option) {
+	o.Unfreeze = true
 }
diff --git a/clock/timecop/timecop_test.go b/clock/timecop/timecop_test.go
index d54d859..eaf1ab3 100644
--- a/clock/timecop/timecop_test.go
+++ b/clock/timecop/timecop_test.go
@@ -52,7 +52,7 @@ func TestSetSpeed(t *testing.T) {
 	})
 	t.Run("on frozen time SetSpeed don't start the time", func(t *testing.T) {
 		now := time.Now()
-		timecop.Travel(t, now, timecop.Freeze())
+		timecop.Travel(t, now, timecop.Freeze)
 		timecop.SetSpeed(t, rnd.Float64())
 		time.Sleep(time.Microsecond)
 		got := clock.Now()
@@ -127,7 +127,7 @@ func TestTravel_timeTime(t *testing.T) {
 			nano   = rnd.IntB(1, int(time.Microsecond-1))
 		)
 		date := time.Date(year, month, day, hour, minute, second, nano, time.Local)
-		timecop.Travel(t, date, timecop.Freeze())
+		timecop.Travel(t, date, timecop.Freeze)
 		time.Sleep(time.Millisecond)
 		got := clock.Now()
 		assert.True(t, date.Equal(got))
@@ -146,13 +146,13 @@ func TestTravel_timeTime(t *testing.T) {
 			nano   = rnd.IntB(1, int(time.Microsecond-1))
 		)
 		date := time.Date(year, month, day, hour, minute, second, nano, time.Local)
-		timecop.Travel(t, date, timecop.Freeze())
+		timecop.Travel(t, date, timecop.Freeze)
 		time.Sleep(time.Millisecond)
 		got := clock.Now()
 		assert.True(t, date.Equal(got))
 		assert.Waiter{WaitDuration: time.Second}.Wait()
 		assert.True(t, date.Equal(clock.Now()))
-		timecop.Travel(t, clock.Now(), timecop.Unfreeze())
+		timecop.Travel(t, clock.Now(), timecop.Unfreeze)
 		assert.MakeRetry(time.Second).Assert(t, func(it assert.It) {
 			it.Must.False(date.Equal(clock.Now()))
 		})
@@ -162,7 +162,7 @@ func TestTravel_timeTime(t *testing.T) {
 func TestTravel_cleanup(t *testing.T) {
 	date := time.Now().AddDate(-10, 0, 0)
 	t.Run("", func(t *testing.T) {
-		timecop.Travel(t, date, timecop.Freeze())
+		timecop.Travel(t, date, timecop.Freeze)
 		assert.Equal(t, date.Year(), clock.Now().Year())
 	})
 	const msg = "was not expected that timecop travel leak out from the sub test"
diff --git a/examples_test.go b/examples_test.go
index 4df1551..ce7d864 100644
--- a/examples_test.go
+++ b/examples_test.go
@@ -1450,7 +1450,7 @@ func Example_clockTimeNow_withTimecop() {
 		CreatedAt: clock.Now(),
 	}
 
-	timecop.Travel(tb, expected.CreatedAt, timecop.Freeze())
+	timecop.Travel(tb, expected.CreatedAt, timecop.Freeze)
 
 	assert.Equal(tb, expected, MyFunc())
 }
@@ -1467,7 +1467,7 @@ func Example_clockTimeNow_withTravelByDate() {
 	var tb testing.TB
 
 	date := time.Date(2022, 01, 01, 12, 0, 0, 0, time.Local)
-	timecop.Travel(tb, date, timecop.Freeze()) // freeze the time until it is read
+	timecop.Travel(tb, date, timecop.Freeze) // freeze the time until it is read
 	time.Sleep(time.Second)
 	_ = clock.Now() // equals with date
 }