Add effect: The signals way of creating side effects

mstniy · Dec 25, 2023 · db8b410 · db8b410
1 parent cc8669c
commit db8b410
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Showing 2 changed files with 22 additions and 0 deletions.
diff --git a/lib/computed.dart b/lib/computed.dart
@@ -35,6 +35,11 @@ class Computed<T> {
       {required T initialPrev, bool memoized = true, bool async = false})
       : _impl = ComputedImpl.withPrev(f, initialPrev, memoized, async);
 
+  /// Defines an "effect", which is a computation meant to have side effects.
+  static ComputedSubscription<void> effect(void Function() f) {
+    return Computed.async(f).listen(null, null);
+  }
+
   /// Subscribes to this computation.
   ///
   /// For non-memoized computations, the listener will be called every time

diff --git a/test/computed_test.dart b/test/computed_test.dart
@@ -22,6 +22,23 @@ void main() {
     expect(flag, true);
   });
 
+  test('effect works', () async {
+    final s = ValueStream(sync: true);
+    s.add(42);
+    int flag = 0;
+
+    final c = $(() => s.use);
+    final effect = Computed.effect(() => flag = c.use);
+
+    await Future.value();
+
+    expect(flag, 42);
+    s.add(43);
+    expect(flag, 43);
+
+    effect.cancel();
+  });
+
   group('streams', () {
     test('can be used as data source', () async {
       final controller = StreamController<int>.broadcast(