Add an IdentityStorageStrategy.

lib/src/graph/strategy.dart

@@ -1,3 +1,4 @@
+import 'strategy/identity.dart';
 import 'strategy/integer.dart';
 import 'strategy/object.dart';
 import 'strategy/positive_integer.dart';
@@ -10,6 +11,9 @@ abstract class StorageStrategy<T> {
  /// Returns a strategy using canonical collection objects.
  factory StorageStrategy.object() = ObjectStorageStrategy;
 
+ /// Returns a strategy using canonical collection objects and object identity.
+ factory StorageStrategy.identity() = IdentityStorageStrategy;
+
  /// Returns a strategy for [int] objects.
  static StorageStrategy<int> integer() => IntegerStorageStrategy();
 

lib/src/graph/strategy/identity.dart

@@ -0,0 +1,12 @@
+import '../strategy.dart';
+
+/// Strategy using canonical collection objects and identity comparison.
+class IdentityStorageStrategy<T> implements StorageStrategy<T> {
+ const IdentityStorageStrategy();
+
+ @override
+ Set<T> createSet() => Set<T>.identity();
+
+ @override
+ Map<T, R> createMap<R>() => Map<T, R>.identity();
+}

test/graph_test.dart

@@ -148,15 +148,34 @@ void main() {
  test('set', () {
  final set = strategy.createSet();
  set.addAll(['foo', 'bar', 'foo']);
- expect(set, ['foo', 'bar']);
+ expect(set, hasLength(2));
+ expect(set, unorderedEquals(['foo', 'bar']));
  });
  test('map', () {
  final map = strategy.createMap<int>();
  map['foo'] = 42;
  map['bar'] = 43;
+ expect(map, hasLength(2));
  expect(map, {'foo': 42, 'bar': 43});
  });
  });
+ group('identity', () {
+ final strategy = StorageStrategy<Point<int>>.identity();
+ final first = const Point(1, 2),
+ second = const Point(2, 3) - const Point(1, 1);
+ test('set', () {
+ final set = strategy.createSet();
+ set.addAll([first, second]);
+ expect(set, unorderedEquals([first, second]));
+ });
+ test('map', () {
+ final map = strategy.createMap<int>();
+ map[first] = 42;
+ map[second] = 43;
+ expect(map.keys, unorderedEquals([first, second]));
+ expect(map.values, unorderedEquals([42, 43]));
+ });
+ });
  group('integer', () {
  final strategy = StorageStrategy.integer();
  test('set', () {