Relax typing on Stream.transform

sdk/lib/async/stream.dart

 // Copyright (c) 2013, 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.
 
 part of dart.async;
 
 // -------------------------------------------------------------------
 // Core Stream types
 // -------------------------------------------------------------------
 
@@ skipping 597 matching lines @@
    * ```
    * stream.map(mapping).transform(transformation).toList()
    * ```
    * which can be more convenient than calling `bind` directly.
    *
    * The [streamTransformer] can return any stream.
    * Whether the returned stream is a broadcast stream or not,
    * and which elements it will contain,
    * is entirely up to the transformation.
    */
-  Stream<S> transform<S>(StreamTransformer<T, S> streamTransformer) {
-    return streamTransformer.bind(this);
+  Stream<S> transform<S>(StreamTransformer<dynamic, S> streamTransformer) {
+    return streamTransformer.bind(this.map<T>((x) => x));

[vsm, 2017/06/26 18:28:51]

Actually, not sure the map is necessary at this point.  Seems to work without
it.

[Lasse Reichstein Nielsen, 2017/06/27 05:45:18]

It should work, the transformer claims to handle all types, so there should be
no need to change the type of elements put into it. 

It's only due to implicit down-cast that the map operation is allowed. You are
implicitly casting `dynamic` to `T` in the `=> x` return, so you'll get a
dynamic check there.

   }
 
   /**
    * Combines a sequence of values by repeatedly applying [combine].
    *
    * Similar to [Iterable.reduce], this function maintains a value,
    * starting with the first element of the stream
    * and updated for each further element of this stream.
    * For each element after the first,
    * the value is updated to the result of calling [combine]
@@ skipping 1360 matching lines @@
   }
 
   void addError(error, [StackTrace stackTrace]) {
     _sink.addError(error, stackTrace);
   }
 
   void close() {
     _sink.close();
   }
 }