Add typed wrapper functions to delegate classes.

lib/src/typed/stream.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:collection/collection.dart';
+
+import '../utils.dart';
+import 'stream_subscription.dart';
+
+class TypeSafeStream<T> implements Stream<T> {
+  final Stream _stream;
+
+  Future<T> get first async => (await _stream.first) as T;
+  Future<T> get last async => (await _stream.last) as T;
+  Future<T> get single async => (await _stream.single) as T;
+
+  bool get isBroadcast => _stream.isBroadcast;
+  Future<bool> get isEmpty => _stream.isEmpty;
+  Future<int> get length => _stream.length;
+
+  TypeSafeStream(this._stream);
+
+  Stream<T> asBroadcastStream(
+      {void onListen(StreamSubscription<T> subscription),
+      void onCancel(StreamSubscription<T> subscription)}) {
+    return new TypeSafeStream<T>(_stream.asBroadcastStream(
+        onListen: onListen == null
+            ? null
+            : (subscription) =>
+                  onListen(new TypeSafeStreamSubscription<T>(subscription)),
+        onCancel: onCancel == null
+            ? null
+            : (subscription) =>
+                  onCancel(new TypeSafeStreamSubscription<T>(subscription))));
+  }
+
+  // TODO(nweiz): Give this a generic parameter when sdk#26125 is fixed.
+  Stream asyncExpand(Stream convert(T event)) =>
+      _stream.asyncExpand(_validateType(convert));
+
+  // TODO(nweiz): Give this a generic parameter when sdk#26125 is fixed.
+  Stream asyncMap(convert(T event)) => _stream.asyncMap(_validateType(convert));
+
+  Stream<T> distinct([bool equals(T previous, T next)]) =>
+      new TypeSafeStream<T>(_stream.distinct(equals == null
+          ? null
+          : (previous, next) => equals(previous as T, next as T)));
+
+  // TODO(nweiz): Give this a generic parameter when sdk#26125 is fixed.
+  Future drain([futureValue]) => _stream.drain(futureValue);
+
+  Stream/*<S>*/ expand/*<S>*/(Iterable/*<S>*/ convert(T value)) =>
+      _stream.expand(_validateType(convert));
+
+  Future firstWhere(bool test(T element), {Object defaultValue()}) =>
+      _stream.firstWhere(_validateType(test), defaultValue: defaultValue);
+
+  Future lastWhere(bool test(T element), {Object defaultValue()}) =>
+      _stream.lastWhere(_validateType(test), defaultValue: defaultValue);
+
+  Future<T> singleWhere(bool test(T element)) async =>
+      (await _stream.singleWhere(_validateType(test))) as T;
+
+  Future/*<S>*/ fold/*<S>*/(/*=S*/ initialValue,
+          /*=S*/ combine(/*=S*/ previous, T element)) =>
+      _stream.fold(initialValue,
+          (previous, element) => combine(previous, element as T));
+
+  Future forEach(void action(T element)) =>
+      _stream.forEach(_validateType(action));
+
+  Stream<T> handleError(Function onError, {bool test(error)}) =>
+      new TypeSafeStream<T>(_stream.handleError(onError, test: test));
+
+  StreamSubscription<T> listen(void onData(T value),
+          {Function onError, void onDone(), bool cancelOnError}) =>
+      new TypeSafeStreamSubscription<T>(_stream.listen(_validateType(onData),
+          onError: onError, onDone: onDone, cancelOnError: cancelOnError));
+
+  Stream/*<S>*/ map/*<S>*/(/*=S*/ convert(T event)) =>
+      _stream.map(_validateType(convert));
+
+  // Don't forward to `_stream.pipe` because we want the consumer to see the
+  // type-asserted stream.
+  Future pipe(StreamConsumer<T> consumer) =>
+      consumer.addStream(this).then((_) => consumer.close());
+
+  Future<T> reduce(T combine(T previous, T element)) async {
+    var result = await _stream.reduce(
+        (previous, element) => combine(previous as T, element as T));
+    return result as T;
+  }
+
+  Stream<T> skipWhile(bool test(T element)) =>
+      new TypeSafeStream<T>(_stream.skipWhile(_validateType(test)));
+
+  Stream<T> takeWhile(bool test(T element)) =>
+      new TypeSafeStream<T>(_stream.takeWhile(_validateType(test)));
+
+  Stream timeout(Duration timeLimit, {void onTimeout(EventSink sink)}) =>
+      _stream.timeout(timeLimit, onTimeout: onTimeout);
+
+  Future<List<T>> toList() async =>
+      DelegatingList.typed/*<T>*/(await _stream.toList());
+
+  Future<Set<T>> toSet() async =>
+      DelegatingSet.typed/*<T>*/(await _stream.toSet());
+
+  // Don't forward to `_stream.transform` because we want the transformer to see
+  // the type-asserted stream.
+  Stream/*<S>*/ transform/*<S>*/(
+          StreamTransformer<T, dynamic/*=S*/> transformer) =>
+      transformer.bind(this);
+
+  Stream<T> where(bool test(T element)) =>
+      new TypeSafeStream<T>(_stream.where(_validateType(test)));
+
+  Future<bool> every(bool test(T element)) =>
+      _stream.every(_validateType(test));
+
+  Future<bool> any(bool test(T element)) => _stream.any(_validateType(test));
+  Stream<T> skip(int count) => new TypeSafeStream<T>(_stream.skip(count));
+  Stream<T> take(int count) => new TypeSafeStream<T>(_stream.take(count));
+  Future<T> elementAt(int index) async => (await _stream.elementAt(index)) as T;
+  Future<bool> contains(Object needle) => _stream.contains(needle);
+  Future<String> join([String separator = ""]) => _stream.join(separator);
+  String toString() => _stream.toString();
+
+  /// Returns a version of [function] that asserts that its argument is an
+  /// instance of `T`.
+  UnaryFunction/*<dynamic, S>*/ _validateType/*<S>*/(
+          /*=S*/ function(T value)) =>
+      function == null ? null : (value) => function(value as T);
+}