Adding package:listen

pkgs/listen/.gitignore

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+# Don’t commit the following directories created by pub.
+.buildlog
+.pub/
+.dart_tool/
+build/
+packages
+.packages
+
+# Or the files created by dart2js.
+*.dart.js
+*.js_
+*.js.deps
+*.js.map
+
+# Include when developing application packages.
+pubspec.lock

pkgs/listen/CHANGELOG.md

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+## 1.0.0-beta.0
+
+- First release.

pkgs/listen/LICENSE

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+Copyright 2014 The Flutter Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google Inc. nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

pkgs/listen/README.md

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+Very prototype package

pkgs/listen/analysis_options.yaml

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+# https://dart.dev/guides/language/analysis-options
+
+include: package:dart_flutter_team_lints/analysis_options.yaml
+
+analyzer:
+  language:
+    strict-raw-types: true
+
+linter:
+  rules:
+    - avoid_unused_constructor_parameters
+    - cancel_subscriptions
+    - literal_only_boolean_expressions
+    - missing_whitespace_between_adjacent_strings
+    - no_adjacent_strings_in_list
+    - no_runtimeType_toString
+    - unnecessary_await_in_return

pkgs/listen/lib/listen.dart

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+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/// An object that maintains a list of listeners.
+///
+/// The listeners are typically used to notify clients that the object has been
+/// updated.
+///
+/// There are two variants of this interface:
+///
+///  * [ValueListenable], an interface that augments the [Listenable] interface
+///    with the concept of a _current value_.
+///
+///  * [Animation], an interface that augments the [ValueListenable] interface
+///    to add the concept of direction (forward or reverse).
+///
+/// Many classes in the Flutter API use or implement these interfaces. The
+/// following subclasses are especially relevant:
+///
+///  * [ChangeNotifier], which can be subclassed or mixed in to create objects
+///    that implement the [Listenable] interface.
+///
+///  * [ValueNotifier], which implements the [ValueListenable] interface with
+///    a mutable value that triggers the notifications when modified.
+///
+/// The terms "notify clients", "send notifications", "trigger notifications",
+/// and "fire notifications" are used interchangeably.
+///
+/// See also:
+///
+///  * [AnimatedBuilder], a widget that uses a builder callback to rebuild
+///    whenever a given [Listenable] triggers its notifications. This widget is
+///    commonly used with [Animation] subclasses, hence its name, but is by no
+///    means limited to animations, as it can be used with any [Listenable]. It
+///    is a subclass of [AnimatedWidget], which can be used to create widgets
+///    that are driven from a [Listenable].
+///  * [ValueListenableBuilder], a widget that uses a builder callback to
+///    rebuild whenever a [ValueListenable] object triggers its notifications,
+///    providing the builder with the value of the object.
+///  * [InheritedNotifier], an abstract superclass for widgets that use a
+///    [Listenable]'s notifications to trigger rebuilds in descendant widgets
+///    that declare a dependency on them, using the [InheritedWidget] mechanism.
+///  * [Listenable.merge], which creates a [Listenable] that triggers
+///    notifications whenever any of a list of other [Listenable]s trigger their
+///    notifications.
+abstract class Listenable {
+  /// Abstract const constructor. This constructor enables subclasses to provide
+  /// const constructors so that they can be used in const expressions.
+  const Listenable();
+
+  /// Return a [Listenable] that triggers when any of the given [Listenable]s
+  /// themselves trigger.
+  ///
+  /// Once the factory is called, items must not be added or removed from the
+  /// iterable.
+  /// Doing so will lead to memory leaks or exceptions.
+  ///
+  /// The iterable may contain nulls; they are ignored.
+  factory Listenable.merge(Iterable<Listenable?> listenables) =
+      _MergingListenable;
+
+  /// Register a closure to be called when the object notifies its listeners.
+  void addListener(void Function() listener);
+
+  /// Remove a previously registered closure from the list of closures that the
+  /// object notifies.
+  void removeListener(void Function() listener);
+}
+
+/// An interface for subclasses of [Listenable] that expose a [value].
+///
+/// This interface is implemented by [ValueNotifier<T>] and [Animation<T>], and
+/// allows other APIs to accept either of those implementations interchangeably.
+///
+/// See also:
+///
+///  * [ValueListenableBuilder], a widget that uses a builder callback to
+///    rebuild whenever a [ValueListenable] object triggers its notifications,
+///    providing the builder with the value of the object.
+abstract class ValueListenable<T> extends Listenable {
+  /// Abstract const constructor. This constructor enables subclasses to provide
+  /// const constructors so that they can be used in const expressions.
+  const ValueListenable();
+
+  /// The current value of the object. When the value changes, the callbacks
+  /// registered with [addListener] will be invoked.
+  T get value;
+}
+
+class _MergingListenable extends Listenable {
+  _MergingListenable(this._children);
+
+  final Iterable<Listenable?> _children;
+
+  @override
+  void addListener(void Function() listener) {
+    for (final child in _children) {
+      child?.addListener(listener);
+    }
+  }
+
+  @override
+  void removeListener(void Function() listener) {
+    for (final child in _children) {
+      child?.removeListener(listener);
+    }
+  }
+
+  @override
+  String toString() {
+    return 'Listenable.merge([${_children.join(", ")}])';
+  }
+}

pkgs/listen/pubspec.yaml

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+name: listen
+version: 1.0.0-beta.0
+description: Includes core Flutter types Listenable and ValueListenable
+
+environment:
+  sdk: ^3.7.0
+
+dev_dependencies:
+  dart_flutter_team_lints: ^3.5.0
+  test: any

pkgs/listen/test/listen_test.dart

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+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:listen/listen.dart';
+import 'package:test/test.dart';
+
+import 'test_listenable.dart';
+
+void main() {
+  test('Listenable.merge', () {
+    final listenableA = TestListenable();
+    final listenableB = TestListenable();
+
+    final merged = Listenable.merge([listenableA, listenableB]);
+
+    var callCount = 0;
+
+    void testListener() {
+      callCount++;
+    }
+
+    merged.addListener(testListener);
+
+    expect(callCount, 0);
+
+    listenableA.notify();
+    expect(callCount, 1);
+
+    listenableB.notify();
+    expect(callCount, 2);
+
+    merged.removeListener(testListener);
+
+    listenableA.notify();
+    expect(callCount, 2);
+
+    listenableB.notify();
+    expect(callCount, 2);
+  });
+}

pkgs/listen/test/test_listenable.dart

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+import 'package:listen/listen.dart';
+
+class TestListenable extends Listenable {
+  final _listeners = <void Function()>{};
+
+  void notify() {
+    for (final listener in _listeners) {
+      listener();
+    }
+  }
+
+  @override
+  void addListener(void Function() listener) {
+    _listeners.add(listener);
+  }
+
+  @override
+  void removeListener(void Function() listener) {
+    _listeners.remove(listener);
+  }
+}