Warn when adding something to a closed sink and improve documentation

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
 // -------------------------------------------------------------------
 
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    * In case of an error the subscription will automatically cancel (even
    * when it was listening with `cancelOnError` set to `false`).
    *
    * In case of a `done` event the future completes with the given
    * [futureValue].
    */
   Future<E> asFuture<E>([E futureValue]);
 }
 
 /**
- * An interface that abstracts creation or handling of [Stream] events.
+ * A [Sink] that supports adding errors.
+ *
+ * This makes it suitable for capturing the results of asynchronous
+ * computations, which can complete with a value or an error.
+ *
+ * The [EventSink] has been designed to handle asynchronous events from
+ * [Stream]s. See, for example, [Stream.eventTransformed] which uses
+ * `EventSink`s to transform events.
  */
 abstract class EventSink<T> implements Sink<T> {
-  /** Send a data event to a stream. */
+  /**
+   * Adds a data [event] to the sink.
+   *
+   * Must not be called on a closed sink.
+   */
   void add(T event);
 
-  /** Send an async error to a stream. */
-  void addError(Object errorEvent, [StackTrace stackTrace]);
+  /**
+   * Adds an [error] to the sink.
+   *
+   * Must not be called on a closed sink.
+   */
+  void addError(Object error, [StackTrace stackTrace]);
 
-  /** Close the sink. No further events can be added after closing. */
+  /**
+   * Closes the sink.
+   *
+   * Calling this method more than once is allowed, but does nothing.
+   *
+   * Neither [add] nor [addError] must be called after this method.
+   */
   void close();
 }
 
 /** [Stream] wrapper that only exposes the [Stream] interface. */
 class StreamView<T> extends Stream<T> {
   final Stream<T> _stream;
 
   const StreamView(Stream<T> stream)
       : _stream = stream,
         super._internal();
@@ skipping 12 matching lines @@
   }
 }
 
 /**
  * Abstract interface for a "sink" accepting multiple entire streams.
  *
  * A consumer can accept a number of consecutive streams using [addStream],
  * and when no further data need to be added, the [close] method tells the
  * consumer to complete its work and shut down.
  *
- * This class is not just a [Sink<Stream>] because it is also combined with
- * other [Sink] classes, like it's combined with [EventSink] in the
- * [StreamSink] class.
- *
  * The [Stream.pipe] accepts a `StreamConsumer` and will pass the stream
  * to the consumer's [addStream] method. When that completes, it will
  * call [close] and then complete its own returned future.
  */
 abstract class StreamConsumer<S> {
   /**
    * Consumes the elements of [stream].
    *
    * Listens on [stream] and does something for each event.
    *
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    * Returns a future which is completed when the consumer has shut down.
    * If cleaning up can fail, the error may be reported in the returned future,
    * otherwise it completes with `null`.
    */
   Future close();
 }
 
 /**
  * A object that accepts stream events both synchronously and asynchronously.
  *
- * A [StreamSink] unifies the asynchronous methods from [StreamConsumer] and
- * the synchronous methods from [EventSink].
+ * A [StreamSink] combines the methods from [StreamConsumer] and [EventSink].
  *
  * The [EventSink] methods can't be used while the [addStream] is called.
  * As soon as the [addStream]'s [Future] completes with a value, the
  * [EventSink] methods can be used again.
  *
  * If [addStream] is called after any of the [EventSink] methods, it'll
  * be delayed until the underlying system has consumed the data added by the
  * [EventSink] methods.
  *
  * When [EventSink] methods are used, the [done] [Future] can be used to
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   }
 
   void addError(error, [StackTrace stackTrace]) {
     _sink.addError(error, stackTrace);
   }
 
   void close() {
     _sink.close();
   }
 }