From 9390e3839f847c11ec05e418d8b9473edd074d27 Mon Sep 17 00:00:00 2001
From: Rishabh Negi <nrishabh20@gmail.com>
Date: Mon, 25 Oct 2021 19:23:15 +0530
Subject: [PATCH 1/2] --add: randomOrNull()

---
 lib/src/collection/kt_collection.dart | 10 ++++++++++
 test/collection/collection_test.dart  | 26 ++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/lib/src/collection/kt_collection.dart b/lib/src/collection/kt_collection.dart
index f7d4ccc..743eab7 100644
--- a/lib/src/collection/kt_collection.dart
+++ b/lib/src/collection/kt_collection.dart
@@ -36,6 +36,16 @@ extension KtCollectionExtensions<T> on KtCollection<T> {
     return elementAt(r.nextInt(size));
   }
 
+  /// Returns a random element from this collection.
+  ///
+  /// returns null if this collection is empty.
+  T? randomOrNull([math.Random? random]) {
+    final r = random ?? math.Random();
+    final index = r.nextInt(size);
+    if (index >= size) return null;
+    return elementAt(index);
+  }
+
   /// Returns a [KtMutableList] filled with all elements of this collection.
   KtMutableList<T> toMutableList() => KtMutableList<T>.from(iter);
 }
diff --git a/test/collection/collection_test.dart b/test/collection/collection_test.dart
index 291e278..06360b5 100644
--- a/test/collection/collection_test.dart
+++ b/test/collection/collection_test.dart
@@ -140,6 +140,32 @@ void testCollection(KtCollection<T> Function<T>() emptyCollection,
     });
   });
 
+  group("randomOrNull", () {
+    test("random item or null with random parameter", () {
+      final collection = collectionOf(["a", "b", "c"]);
+
+      final firstPick = collection.randomOrNull(NotRandom()..next = 2);
+      final pos2 = collection.elementAt(2);
+      if (ordered) expect(pos2, "c");
+
+      expect(firstPick, pos2);
+
+      final pos0 = collection.elementAt(0);
+      if (ordered) expect(pos0, "a");
+
+      final secondPick = collection.randomOrNull(NotRandom()..next = 0);
+      expect(secondPick, pos0);
+
+      final outOfRangePick = collection.randomOrNull(NotRandom()..next = 3);
+      expect(outOfRangePick, null);
+    });
+
+    test("randomOrNull works without passing a Random", () {
+      final collection = collectionOf(["a", "b", "c"]);
+      expect(collection.randomOrNull(),
+          anyOf(equals("a"), equals("b"), equals("c"), equals(null)));
+    });
+  });
   group("toString", () {
     if (ordered) {
       test("default string representation", () {

From eda96a61d93a6dbdcd29775536b426feacf156ac Mon Sep 17 00:00:00 2001
From: Rishabh Negi <nrishabh20@gmail.com>
Date: Mon, 25 Oct 2021 19:50:53 +0530
Subject: [PATCH 2/2] --update: fix and test for empty collection for
 randomOrNull

---
 lib/src/collection/kt_collection.dart | 1 +
 test/collection/collection_test.dart  | 7 +++++++
 2 files changed, 8 insertions(+)

diff --git a/lib/src/collection/kt_collection.dart b/lib/src/collection/kt_collection.dart
index 743eab7..734f0b7 100644
--- a/lib/src/collection/kt_collection.dart
+++ b/lib/src/collection/kt_collection.dart
@@ -40,6 +40,7 @@ extension KtCollectionExtensions<T> on KtCollection<T> {
   ///
   /// returns null if this collection is empty.
   T? randomOrNull([math.Random? random]) {
+    if (!isNotEmpty()) return null;
     final r = random ?? math.Random();
     final index = r.nextInt(size);
     if (index >= size) return null;
diff --git a/test/collection/collection_test.dart b/test/collection/collection_test.dart
index 06360b5..91e8313 100644
--- a/test/collection/collection_test.dart
+++ b/test/collection/collection_test.dart
@@ -158,12 +158,19 @@ void testCollection(KtCollection<T> Function<T>() emptyCollection,
 
       final outOfRangePick = collection.randomOrNull(NotRandom()..next = 3);
       expect(outOfRangePick, null);
+
+      final emptyCollection = collectionOf([]);
+      final pick1 = emptyCollection.randomOrNull(NotRandom()..next = 0);
+      expect(pick1, null);
     });
 
     test("randomOrNull works without passing a Random", () {
       final collection = collectionOf(["a", "b", "c"]);
       expect(collection.randomOrNull(),
           anyOf(equals("a"), equals("b"), equals("c"), equals(null)));
+
+      final emptyCollection = collectionOf([]);
+      expect(emptyCollection.randomOrNull(), equals(null));
     });
   });
   group("toString", () {