Avoid unnecessary observable notifications of @observable `Iterable…

…` or `Map` fields

mobx/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.2.2
+
+- Avoid unnecessary observable notifications of `@observable` `Iterable` or `Map` fields of Stores by [@amondnet](https://github.com/amondnet)
+
 ## 2.2.1
 
 - Reduces unnecessary iterations while using `Iterables` with `addAll`, `insertAll`, `replaceRange`, `setAll` and `setRange` methods. [#942](https://github.com/mobxjs/mobx.dart/pull/942).

mobx/lib/src/core/atom_extensions.dart

@@ -1,3 +1,4 @@
+import 'package:collection/collection.dart';
 import 'package:mobx/mobx.dart';
 
 extension AtomSpyReporter on Atom {
@@ -8,8 +9,9 @@ extension AtomSpyReporter on Atom {
 
   void reportWrite<T>(T newValue, T oldValue, void Function() setNewValue,
       {EqualityComparer<T>? equals}) {
-    final areEqual =
-        equals == null ? oldValue == newValue : equals(oldValue, newValue);
+    final areEqual = equals == null
+        ? _equals(oldValue, newValue)
+        : equals(oldValue, newValue);
 
     // Avoid unnecessary observable notifications of @observable fields of Stores
     if (areEqual) {
@@ -31,3 +33,19 @@ extension AtomSpyReporter on Atom {
     context.spyReport(EndedSpyEvent(type: 'observable', name: name));
   }
 }
+
+/// Determines whether [a] and [b] are equal.
+bool _equals<T>(T a, T b) {
+  if (identical(a, b)) return true;
+  if (a is Iterable || a is Map) {
+    if (!_equality.equals(a, b)) return false;
+  } else if (a.runtimeType != b.runtimeType) {
+    return false;
+  } else if (a != b) {
+    return false;
+  }
+
+  return true;
+}
+
+const DeepCollectionEquality _equality = DeepCollectionEquality();

mobx/pubspec.yaml

@@ -1,5 +1,5 @@
 name: mobx
-version: 2.2.1
+version: 2.2.2
 description: "MobX is a library for reactively managing the state of your applications. Use the power of observables, actions, and reactions to supercharge your Dart and Flutter apps."
 
 homepage: https://github.com/mobxjs/mobx.dart
@@ -10,10 +10,10 @@ environment:
 
 dependencies:
   meta: ^1.3.0
+  collection: ^1.15.0
 
 dev_dependencies:
   build_runner: ^2.0.6
-  collection: ^1.15.0
   coverage: ^1.0.1
   fake_async: ^1.2.0
   lints: ^2.0.0

mobx/test/atom_extensions_test.dart

@@ -68,6 +68,54 @@ void main() {
 
     expect(autorunResults, ['first', 'second']);
   });
+
+  test(
+      'when write to @observable iterable field with unchanged value, should not trigger notifications for downstream',
+      () {
+    final store = _ExampleStore();
+
+    final autorunResults = <List<String>>[];
+    autorun((_) => autorunResults.add(store.list));
+
+    store.list = ['first'];
+    expect(autorunResults, [
+      ['first']
+    ]);
+
+    store.list = ['first'];
+    expect(autorunResults, [
+      ['first']
+    ]);
+
+    store.list = ['first'];
+    expect(autorunResults, [
+      ['first']
+    ]);
+  });
+
+  test(
+      'when write to @observable map field with unchanged value, should not trigger notifications for downstream',
+      () {
+    final store = _ExampleStore();
+
+    final autorunResults = <Map<String, int>>[];
+    autorun((_) => autorunResults.add(store.map));
+
+    store.map = {'first': 1};
+    expect(autorunResults, [
+      {'first': 1}
+    ]);
+
+    store.map = {'first': 1};
+    expect(autorunResults, [
+      {'first': 1}
+    ]);
+
+    store.map = {'first': 1};
+    expect(autorunResults, [
+      {'first': 1}
+    ]);
+  });
 }
 
 class _ExampleStore = __ExampleStore with _$_ExampleStore;
@@ -83,6 +131,12 @@ abstract class __ExampleStore with Store {
 
   @MakeObservable(equals: _equals)
   String value3 = 'first';
+
+  @observable
+  List<String> list = ['first'];
+
+  @observable
+  Map<String, int> map = {'first': 1};
 }
 
 // This is what typically a mobx codegen will generate.
@@ -138,4 +192,36 @@ mixin _$_ExampleStore on __ExampleStore, Store {
         equals: (String? oldValue, String? newValue) =>
             oldValue?.length == newValue?.length);
   }
+
+  // ignore: non_constant_identifier_names
+  late final _$listAtom = Atom(name: '__ExampleStore.list', context: context);
+
+  @override
+  List<String> get list {
+    _$listAtom.reportRead();
+    return super.list;
+  }
+
+  @override
+  set list(List<String> value) {
+    _$listAtom.reportWrite(value, super.list, () {
+      super.list = value;
+    });
+  }
+
+  // ignore: non_constant_identifier_names
+  late final _$mapAtom = Atom(name: '__ExampleStore.map', context: context);
+
+  @override
+  Map<String, int> get map {
+    _$mapAtom.reportRead();
+    return super.map;
+  }
+
+  @override
+  set map(Map<String, int> value) {
+    _$mapAtom.reportWrite(value, super.map, () {
+      super.map = value;
+    });
+  }
 }