Merge pull request #133 from rishabhdeepsingh/nullable_num

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 {

lib/dartx.dart

@@ -13,6 +13,7 @@ import 'package:crypto/crypto.dart' as crypto;
 export 'package:characters/characters.dart';
 export 'package:time/time.dart';
 
+part 'src/arithmetic.dart';
 part 'src/comparable.dart';
 part 'src/comparator.dart';
 part 'src/function.dart';

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?;
+}

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);
+    });
+  });
+}