Merge pull request #120 from jinyus/guarded-disposal

Add disposal guard for beacons

packages/state_beacon_core/lib/src/extensions/wrap.dart

@@ -71,7 +71,7 @@ extension WritableWrap<T, U> on BeaconWrapper<T, U> {
       });
 
       onDispose(() {
-        if (isDisposing) return;
+        if (isDisposing || target._guarded) return;
         isDisposing = true;
         target.dispose();
       });

packages/state_beacon_core/lib/src/producer.dart

@@ -95,6 +95,23 @@ abstract class Producer<T> implements Disposable {
     }
   }
 
+  /// This is true if the beacon is guarded from being disposed by
+  /// its dependants.
+  bool _guarded = false;
+
+  /// Prevents the beacon from being disposed by its dependants.
+  /// The beacon will still be disposed if its dependencies are disposed.
+  ///
+  /// ```dart
+  /// final number = Beacon(0)..guard();
+  /// final doubled = number.map((value) => value * 2);
+  /// doubled.dispose();
+  /// number.disposed; // false
+  /// ```
+  void guard() {
+    _guarded = true;
+  }
+
   /// The number of listeners subscribed to this beacon.
   int get listenersCount => _observers.length;
 

packages/state_beacon_core/test/src/beacons/readable_test.dart

@@ -167,4 +167,26 @@ void main() {
     beacon.value = 1;
     beacon.value = 2;
   });
+
+  test('should not dispose when dependant is disposed when guarded', () {
+    final number = Beacon.writable(0);
+
+    number.guard();
+
+    final doubled = number.map((value) => value * 2);
+
+    doubled.dispose();
+
+    expect(number.isDisposed, false);
+  });
+
+  test('should dispose when dependant is disposed when not guarded', () {
+    final number = Beacon.writable(0);
+
+    final doubled = number.map((value) => value * 2);
+
+    doubled.dispose();
+
+    expect(number.isDisposed, true);
+  });
 }