From 9e878ab7ea445b540ea3b6a1c130eb3f6eb464b9 Mon Sep 17 00:00:00 2001
From: rishabhdeepsingh <rishabhdeepsingh98@gmail.com>
Date: Wed, 9 Jun 2021 00:05:03 +0530
Subject: [PATCH] added arithmetic plus and minus for num class

---
 example/main.dart         |  2 ++
 lib/dartx.dart            |  1 +
 lib/src/arithmetic.dart   | 15 ++++++++
 test/arithmetic_test.dart | 74 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 92 insertions(+)
 create mode 100644 lib/src/arithmetic.dart
 create mode 100644 test/arithmetic_test.dart

diff --git a/example/main.dart b/example/main.dart
index da45083..954be8d 100644
--- a/example/main.dart
+++ b/example/main.dart
@@ -28,6 +28,8 @@ void main() {
     [4, 5, 6]
   ];
   final flattened = nestedList.flatten(); // [1, 2, 3, 4, 5, 6]
+
+  123.0.minus(null); // 123.0
 }
 
 class Dog {
diff --git a/lib/dartx.dart b/lib/dartx.dart
index 4b159f4..2dc98fc 100644
--- a/lib/dartx.dart
+++ b/lib/dartx.dart
@@ -13,6 +13,7 @@ import 'package:crypto/crypto.dart' as crypto;
 export 'package:time/time.dart';
 export 'package:characters/characters.dart';
 
+part 'src/arithmetic.dart';
 part 'src/comparable.dart';
 part 'src/comparator.dart';
 part 'src/function.dart';
diff --git a/lib/src/arithmetic.dart b/lib/src/arithmetic.dart
new file mode 100644
index 0000000..57620fa
--- /dev/null
+++ b/lib/src/arithmetic.dart
@@ -0,0 +1,15 @@
+part of dartx;
+
+extension NumArithmeticX<T extends num> on T {
+  /// Minus val if if it not null else returns `this`
+  T? minus(T? val) => val == null ? this : this - val as T?;
+
+  /// returns null if val is null else returns `this` - val
+  T? minusOrNull(T? val) => val == null ? null : this - val as T?;
+
+  /// Adds val if if it not null else returns `this`
+  T? plus(T? val) => val == null ? this : this + val as T?;
+
+  /// returns null if val is null else returns `this` + val
+  T? plusOrNull(T? val) => val == null ? null : this + val as T?;
+}
diff --git a/test/arithmetic_test.dart b/test/arithmetic_test.dart
new file mode 100644
index 0000000..7a503d4
--- /dev/null
+++ b/test/arithmetic_test.dart
@@ -0,0 +1,74 @@
+import 'package:test/test.dart';
+import 'package:dartx/dartx.dart';
+
+void main() {
+  group('num', () {
+    test('num?.plus() and num?.minus()', () {
+      const num? value = null;
+      expect(value?.minus(1), null);
+      expect(value?.minus(1) ?? -1, -1);
+      expect((value ?? 0) - 1, -1);
+
+      expect(value?.plus(1), null);
+      expect(value?.plus(1) ?? 1, 1);
+      expect((value ?? 0) + 1, 1);
+    });
+    test('num?.plusOrNull() and num?.minusOrNull()', () {
+      const num? value = null;
+      const num one = 1;
+      expect(one.plus(value), 1);
+      expect(one.plusOrNull(value), null);
+      expect(one.plusOrNull(value) ?? 1, 1);
+
+      expect(one.minus(value), 1);
+      expect(one.minusOrNull(value), null);
+      expect(one.minusOrNull(value) ?? 1, 1);
+    });
+  });
+
+  group('int', () {
+    test('int?.plus() and int?.minus()', () {
+      const int? value = null;
+      expect(value?.minus(1), null);
+      expect(value?.minus(1) ?? -1, -1);
+      expect((value ?? 0) - 1, -1);
+
+      expect(value?.plus(1), null);
+      expect(value?.plus(1) ?? 1, 1);
+      expect((value ?? 0) + 1, 1);
+    });
+    test('int?.plusOrNull() and int?.minusOrNull()', () {
+      const int? value = null;
+      expect(1.plus(value), 1);
+      expect(1.plusOrNull(value), null);
+      expect(1.plusOrNull(value) ?? 1, 1);
+
+      expect(1.minus(value), 1);
+      expect(1.minusOrNull(value), null);
+      expect(1.minusOrNull(value) ?? 1, 1);
+    });
+  });
+
+  group('double', () {
+    test('double?.plus() and double?.minus()', () {
+      const double? value = null;
+      expect(value?.minus(1), null);
+      expect(value?.minus(1) ?? -1, -1);
+      expect((value ?? 0) - 1, -1);
+
+      expect(value?.plus(1), null);
+      expect(value?.plus(1) ?? 1, 1);
+      expect((value ?? 0) + 1, 1);
+    });
+    test('double?.plusOrNull() and double?.minusOrNull()', () {
+      const double? value = null;
+      expect(1.0.plus(value), 1.0);
+      expect(1.0.plusOrNull(value), null);
+      expect(1.0.plusOrNull(value) ?? 1.0, 1.0);
+
+      expect(1.0.minus(value), 1.0);
+      expect(1.0.minusOrNull(value), null);
+      expect(1.0.minusOrNull(value) ?? 1.0, 1.0);
+    });
+  });
+}