Allow a custom equals parameter for observable collections

mobx/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.2.4
+
+- Allow a custom equals parameter for observable collections( ObservableList, ObservableMap, ObservableSet ) - [@amondnet](https://github.com/amondnet)
+
 ## 2.2.3
 
 - Avoid unnecessary observable notifications of `@observable` `Iterable` or `Map` fields of Stores by [@amondnet](https://github.com/amondnet)  in [#951](https://github.com/mobxjs/mobx.dart/pull/951)

mobx/lib/src/api/observable_collections.dart

@@ -1,8 +1,10 @@
 import 'dart:collection';
 import 'dart:math';
 
+import 'package:collection/collection.dart';
 import 'package:meta/meta.dart';
 import 'package:mobx/mobx.dart';
+import 'package:mobx/src/utils.dart';
 
 part 'observable_collections/observable_list.dart';
 part 'observable_collections/observable_map.dart';

mobx/lib/src/api/observable_collections/observable_list.dart

@@ -25,20 +25,23 @@
         ListMixin<T>
     implements
         Listenable<ListChange<T>> {
-  ObservableList({ReactiveContext? context, String? name})
-      : this._wrap(context, _observableListAtom<T>(context, name), []);
+  ObservableList(
+      {ReactiveContext? context, String? name, EqualityComparer<T>? equals})
+      : this._wrap(context, _observableListAtom<T>(context, name), [], equals);
 
   ObservableList.of(Iterable<T> elements,
-      {ReactiveContext? context, String? name})
+      {ReactiveContext? context, String? name, EqualityComparer<T>? equals})
       : this._wrap(context, _observableListAtom<T>(context, name),
-            List<T>.of(elements, growable: true));
+            List<T>.of(elements, growable: true), equals);
 
-  ObservableList._wrap(ReactiveContext? context, this._atom, this._list)
+  ObservableList._wrap(
+      ReactiveContext? context, this._atom, this._list, this._equals)
       : _context = context ?? mainContext;
 
   final ReactiveContext _context;
   final Atom _atom;
   final List<T> _list;
+  final EqualityComparer<T>? _equals;
 
   List<T> get nonObservableInner => _list;
 
@@ -96,7 +99,7 @@
     _context.conditionallyRunInAction(() {
       final oldValue = _list[index];
 
-      if (oldValue != value) {
+      if (!_areEquals(oldValue, value)) {
         _list[index] = value;
         _notifyElementUpdate(index, value, oldValue);
       }
@@ -167,10 +170,18 @@
   }
 
   @override
-  Map<int, T> asMap() => ObservableMap._wrap(_context, _list.asMap(), _atom);
+  Map<int, T> asMap() =>
+      ObservableMap._wrap(_context, _list.asMap(), _atom, _equals);
 
   @override
-  List<R> cast<R>() => ObservableList._wrap(_context, _atom, _list.cast<R>());
+  List<R> cast<R>([EqualityComparer<R>? equals]) => ObservableList._wrap(
+      _context,
+      _atom,
+      _list.cast<R>(),
+      equals ??
+          (_equals != null
+              ? (R? a, R? b) => _equals!(a as T?, b as T?)
+              : null));
 
   @override
   List<T> toList({bool growable = true}) {
@@ -184,7 +195,7 @@
   set first(T value) {
     _context.conditionallyRunInAction(() {
       final oldValue = _list.first;
-      if (oldValue != value) {
+      if (!_areEquals(oldValue, value)) {
         _list.first = value;
         _notifyElementUpdate(0, value, oldValue);
       }
@@ -376,7 +387,7 @@
         for (var i = 0; i < _list.length; ++i) {
           final oldValue = oldList[i];
           final newValue = _list[i];
-          if (newValue != oldValue) {
+          if (!_areEquals(oldValue, newValue)) {
             changes.add(ElementChange(
                 index: i, oldValue: oldValue, newValue: newValue));
           }
@@ -398,7 +409,7 @@
         for (var i = 0; i < _list.length; ++i) {
           final oldValue = oldList[i];
           final newValue = _list[i];
-          if (newValue != oldValue) {
+          if (!_areEquals(oldValue, newValue)) {
             changes.add(ElementChange(
                 index: i, oldValue: oldValue, newValue: newValue));
           }
@@ -456,6 +467,14 @@
 
     _listeners.notifyListeners(change);
   }
+
+  bool _areEquals(T? a, T? b) {
+    if (_equals != null) {
+      return _equals!(a, b);
+    } else {
+      return equatable(a, b);
+    }
+  }
 }
 
 typedef ListChangeListener<TNotification> = void Function(
@@ -520,4 +539,4 @@
 /// Used during testing for wrapping a regular `List<T>` as an `ObservableList<T>`
 @visibleForTesting
 ObservableList<T> wrapInObservableList<T>(Atom atom, List<T> list) =>
-    ObservableList._wrap(mainContext, atom, list);
+    ObservableList._wrap(mainContext, atom, list, null);

mobx/lib/src/api/observable_collections/observable_map.dart

@@ -26,37 +26,45 @@
         MapMixin<K, V>
     implements
         Listenable<MapChange<K, V>> {
-  ObservableMap({ReactiveContext? context, String? name})
+  ObservableMap(
+      {ReactiveContext? context, String? name, EqualityComparer<V>? equals})
       : _context = context ?? mainContext,
         _atom = _observableMapAtom<K, V>(context, name),
-        _map = <K, V>{};
+        _map = <K, V>{},
+        _equals = equals;
 
-  ObservableMap.of(Map<K, V> other, {ReactiveContext? context, String? name})
+  ObservableMap.of(Map<K, V> other,
+      {ReactiveContext? context, String? name, EqualityComparer<V>? equals})
       : _context = context ?? mainContext,
         _atom = _observableMapAtom<K, V>(context, name),
-        _map = Map.of(other);
+        _map = Map.of(other),
+        _equals = equals;
 
   ObservableMap.linkedHashMapFrom(Map<K, V> other,
-      {ReactiveContext? context, String? name})
+      {ReactiveContext? context, String? name, EqualityComparer<V>? equals})
       : _context = context ?? mainContext,
         _atom = _observableMapAtom<K, V>(context, name),
-        _map = LinkedHashMap.from(other);
+        _map = LinkedHashMap.from(other),
+        _equals = equals;
 
   ObservableMap.splayTreeMapFrom(Map<K, V> other,
       {int Function(K, K)? compare,
       // ignore: avoid_annotating_with_dynamic
       bool Function(dynamic)? isValidKey,
       ReactiveContext? context,
-      String? name})
+      String? name,
+      EqualityComparer<V>? equals})
       : _context = context ?? mainContext,
         _atom = _observableMapAtom<K, V>(context, name),
-        _map = SplayTreeMap.from(other, compare, isValidKey);
+        _map = SplayTreeMap.from(other, compare, isValidKey),
+        _equals = equals;
 
-  ObservableMap._wrap(this._context, this._map, this._atom);
+  ObservableMap._wrap(this._context, this._map, this._atom, this._equals);
 
   final ReactiveContext _context;
   final Atom _atom;
   final Map<K, V> _map;
+  final EqualityComparer<V>? _equals;
 
   Map<K, V> get nonObservableInner => _map;
 
@@ -94,7 +102,7 @@
         }
       }
 
-      if (!_map.containsKey(key) || value != oldValue) {
+      if (!_map.containsKey(key) || !_areEquals(value, oldValue)) {
         _map[key] = value;
         if (type == 'update') {
           _reportUpdate(key, value, oldValue);
@@ -127,8 +135,15 @@
   Iterable<K> get keys => MapKeysIterable(_map.keys, _atom);
 
   @override
-  Map<RK, RV> cast<RK, RV>() =>
-      ObservableMap._wrap(_context, super.cast(), _atom);
+  Map<RK, RV> cast<RK, RV>([EqualityComparer<RV>? equals]) =>
+      ObservableMap._wrap(
+          _context,
+          super.cast(),
+          _atom,
+          equals ??
+              (_equals == null
+                  ? null
+                  : (RV? a, RV? b) => _equals!(a as V?, b as V?)));
 
   @override
   V? remove(Object? key) {
@@ -231,13 +246,21 @@
     }
     return _listeners.add(listener);
   }
+
+  bool _areEquals(V? a, V? b) {
+    if (_equals != null) {
+      return _equals!(a, b);
+    } else {
+      return equatable(a, b);
+    }
+  }
 }
 
 /// A convenience method to wrap the standard `Map<K,V>` in an `ObservableMap<K,V>`.
 /// This is mostly to aid in testing.
 @visibleForTesting
 ObservableMap<K, V> wrapInObservableMap<K, V>(Atom atom, Map<K, V> map) =>
-    ObservableMap._wrap(mainContext, map, atom);
+    ObservableMap._wrap(mainContext, map, atom, null);
 
 typedef MapChangeListener<K, V> = void Function(MapChange<K, V>);