supported civil date for period

period.go

@@ -11,7 +11,7 @@ import (
 )
 
 type timeish[T TimeZone] interface {
-	Time[T] | time.Time | constraints.Bytes
+	Time[T] | time.Time | Date[T] | constraints.Bytes
 }
 
 var stringType = reflect.TypeOf("")
@@ -194,6 +194,8 @@ func convertTime[T TimeZone](arg any) (Time[T], error) {
 		return v, nil
 	case time.Time:
 		return In[T](v), nil
+	case Date[T]:
+		return v.Time(), nil
 	case string:
 		return ParseISO[T](v)
 	case []byte:

period_test.go

@@ -46,6 +46,27 @@ func TestPeriod_Slice(t *testing.T) {
 			t.Fatalf("(-want, +got)\n%s", diff)
 		}
 	})
+	t.Run("Date[UTC] params", func(t *testing.T) {
+		period, err := NewPeriod[tz.UTC](
+			Date[tz.UTC]{
+				Year:  2014,
+				Month: 2,
+				Day:   5,
+			},
+			Date[tz.UTC]{
+				Year:  2014,
+				Month: 2,
+				Day:   8,
+			},
+		)
+		if err != nil {
+			t.Fatal(err)
+		}
+		got := period.PeriodicDuration(24 * time.Hour).Slice()
+		if diff := cmp.Diff(want, got); diff != "" {
+			t.Fatalf("(-want, +got)\n%s", diff)
+		}
+	})
 	t.Run("time.Time params", func(t *testing.T) {
 		period, err := NewPeriod[tz.UTC](
 			time.Date(2014, 2, 5, 0, 0, 0, 0, time.UTC),