refactor!: isEnabled getter and setter

packages/forge2d/lib/src/dynamics/contacts/contact.dart

@@ -161,19 +161,21 @@ abstract class Contact {
             this.indexB == indexA);
   }
 
-  /// Enable/disable this contact. This can be used inside the pre-solve contact
-  /// listener. The contact is only disabled for the current time step
-  /// (or sub-step in continuous collisions).
-  void setEnabled(bool enable) {
-    if (enable) {
+  /// Enable or disable this contact.
+  ///
+  /// This can be used inside [ContactListener.preSolve]. The contact is
+  /// only disabled for the current time step (or sub-step in continuous
+  /// collisions).
+  set isEnabled(bool value) {
+    if (value) {
       flags |= enabledFlag;
     } else {
       flags &= ~enabledFlag;
     }
   }
 
-  /// Has this contact been disabled?
-  bool isEnabled() => (flags & enabledFlag) == enabledFlag;
+  /// Whether this contact is enabled.
+  bool get isEnabled => (flags & enabledFlag) == enabledFlag;
 
   void resetFriction() {
     _friction = Contact.mixFriction(fixtureA.friction, fixtureB.friction);

packages/forge2d/lib/src/dynamics/world.dart

@@ -565,7 +565,7 @@ class World {
           }
 
           // Is this contact solid and touching?
-          if (contact.isEnabled() == false || contact.isTouching() == false) {
+          if (contact.isEnabled == false || contact.isTouching() == false) {
             continue;
           }
 
@@ -681,7 +681,7 @@ class World {
 
       for (final contact in contactManager.contacts) {
         // Is this contact disabled?
-        if (contact.isEnabled() == false) {
+        if (contact.isEnabled == false) {
           continue;
         }
 
@@ -798,9 +798,9 @@ class World {
       ++minContact.toiCount;
 
       // Is the contact solid?
-      if (minContact.isEnabled() == false || minContact.isTouching() == false) {
+      if (minContact.isEnabled == false || minContact.isTouching() == false) {
         // Restore the sweeps.
-        minContact.setEnabled(false);
+        minContact.isEnabled = false;
         bodyA.sweep.set(_backup1);
         bodyB.sweep.set(_backup2);
         bodyA.synchronizeTransform();
@@ -855,7 +855,7 @@ class World {
             contact.update(contactManager.contactListener);
 
             // Was the contact disabled by the user?
-            if (contact.isEnabled() == false) {
+            if (contact.isEnabled == false) {
               other.sweep.set(_backup1);
               other.synchronizeTransform();
               continue;

packages/forge2d/test/dynamics/contacts/contact_test.dart

@@ -0,0 +1,78 @@
+import 'package:forge2d/forge2d.dart';
+import 'package:mocktail/mocktail.dart';
+import 'package:test/test.dart';
+
+class _MockFixture extends Mock implements Fixture {}
+
+class _TestContact extends Contact {
+  _TestContact(
+    super.fixtureA,
+    super.indexA,
+    super.fixtureB,
+    super.indexB,
+  );
+
+  @override
+  void evaluate(_, __, ___) => throw UnimplementedError();
+}
+
+void main() {
+  group('Contact', () {
+    late Fixture fixtureA;
+    late int indexA;
+    late Fixture fixtureB;
+    late int indexB;
+
+    setUp(() {
+      fixtureA = _MockFixture();
+      when(() => fixtureA.friction).thenReturn(0);
+      when(() => fixtureA.restitution).thenReturn(0);
+
+      fixtureB = _MockFixture();
+      when(() => fixtureB.friction).thenReturn(0);
+      when(() => fixtureB.restitution).thenReturn(0);
+
+      indexA = 0;
+      indexB = 0;
+    });
+
+    test('can be instantiated', () {
+      expect(
+        _TestContact(
+          fixtureA,
+          indexA,
+          fixtureB,
+          indexB,
+        ),
+        isA<Contact>(),
+      );
+    });
+
+    group('isEnabled', () {
+      test('true by default', () {
+        final contact = _TestContact(
+          fixtureA,
+          indexA,
+          fixtureB,
+          indexB,
+        );
+
+        expect(contact.isEnabled, isTrue);
+      });
+
+      test('can change', () {
+        final contact = _TestContact(
+          fixtureA,
+          indexA,
+          fixtureB,
+          indexB,
+        );
+
+        final newIsEnabled = !contact.isEnabled;
+        contact.isEnabled = newIsEnabled;
+
+        expect(contact.isEnabled, equals(newIsEnabled));
+      });
+    });
+  });
+}