Support shuffle for iter

cities.go

@@ -7,8 +7,14 @@ import (
 	"strconv"
 )
 
-//go:embed upstream/cities.json
-var citiesbytes []byte
+var (
+	//go:embed upstream/cities.json
+	citiesbytes []byte
+
+	Cities []*City
+
+	idx []int
+)
 
 type City struct {
 	Country string  `json:"country"`
@@ -19,8 +25,6 @@ type City struct {
 	Admin2  string  `json:"admin2"`
 }
 
-var Cities []*City
-
 func init() {
 	type RawCity struct {
 		Country string `json:"country"`
@@ -35,7 +39,7 @@ func init() {
 	if err := json.Unmarshal(citiesbytes, &rawcities); err != nil {
 		panic(err)
 	}
-	for _, rawcity := range rawcities {
+	for i, rawcity := range rawcities {
 		lat, err := strconv.ParseFloat(rawcity.Lat, 64)
 		if err != nil {
 			panic(err)
@@ -52,5 +56,6 @@ func init() {
 			Admin1:  rawcity.Admin1,
 			Admin2:  rawcity.Admin2,
 		})
+		idx = append(idx, i)
 	}
 }

iter.go

@@ -3,22 +3,33 @@
 
 package gocitiesjson
 
-import "iter"
+import (
+	"iter"
+	"math/rand"
+)
 
-func All() iter.Seq[*City] {
+func All(shuffle bool) iter.Seq[*City] {
 	return func(yield func(*City) bool) {
-		for _, city := range Cities {
-			if !yield(city) {
+		var idxes []int
+		if shuffle {
+			idxes = make([]int, len(idx))
+			copy(idxes, idx)
+			rand.Shuffle(len(idxes), func(i, j int) { idxes[i], idxes[j] = idxes[j], idxes[i] })
+		} else {
+			idxes = idx
+		}
+		for _, i := range idxes {
+			if !yield(Cities[i]) {
 				return
 			}
 		}
 	}
 }
 
-func Filter(filter func(*City) bool) iter.Seq[*City] {
+func Filter(fn func(*City) bool, shuffle bool) iter.Seq[*City] {
 	return func(yield func(*City) bool) {
-		for _, city := range Cities {
-			if filter(city) {
+		for city := range All(shuffle) {
+			if fn(city) {
 				if !yield(city) {
 					return
 				}

iter_test.go

@@ -11,7 +11,7 @@ import (
 
 func ExampleAll() {
 	c := 0
-	for city := range gocitiesjson.All() {
+	for city := range gocitiesjson.All(false) {
 		_ = city
 		c++
 	}
@@ -25,7 +25,7 @@ func ExampleFilter() {
 	bboxFilter := func(city *gocitiesjson.City) bool {
 		return city.Lng > 0 && city.Lng < 10 && city.Lat > 0 && city.Lat < 10
 	}
-	for city := range gocitiesjson.Filter(bboxFilter) {
+	for city := range gocitiesjson.Filter(bboxFilter, false) {
 		_ = city
 		c++
 	}