Add typed wrapper functions to delegate classes.

lib/src/lazy_stream.dart

 // Copyright (c) 2015, 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 "stream_completer.dart";
+import "delegate/stream.dart";
 
 /// A [Stream] wrapper that forwards to another [Stream] that's initialized
 /// lazily.
 ///
 /// This class allows a concrete `Stream` to be created only once it has a
 /// listener. It's useful to wrapping APIs that do expensive computation to
 /// produce a `Stream`.
 class LazyStream<T> extends Stream<T> {
   /// The callback that's called to create the inner stream.
   ZoneCallback _callback;
@@ skipping 14 matching lines @@
     if (_callback == null) {
       throw new StateError("Stream has already been listened to.");
     }
 
     // Null out the callback before we invoke it to ensure that even while
     // running it, this can't be called twice.
     var callback = _callback;
     _callback = null;
     var result = callback();
 
-    Stream stream = result is Future
-        ? StreamCompleter.fromFuture(result)
-        : result;
+    Stream<T> stream;
+    if (result is Future) {
+      stream = StreamCompleter.fromFuture(result.then((stream) {
+        return DelegatingStream.typed/*<T>*/(stream as Stream);
+      }));

[Lasse Reichstein Nielsen, 2016/04/08 09:20:29]

I still don't like having an async function producing a stream - a
Future<Stream>.
The callback should be using a StreamCompleter instead and just return a Stream.

[nweiz, 2016/04/11 20:26:16]

I still think it's fine :).

+    } else {
+      stream = DelegatingStream.typed/*<T>*/(result as Stream);
+    }
 
     return stream.listen(onData,
         onError: onError, onDone: onDone, cancelOnError: cancelOnError);
   }
 }