Steps towards making the convert library strong-mode compliant.

sdk/lib/convert/chunked_conversion.dart

Index: sdk/lib/convert/chunked_conversion.dart
diff --git a/sdk/lib/convert/chunked_conversion.dart b/sdk/lib/convert/chunked_conversion.dart
index 4c962eb62c589db90f57512002408d7f12e931be..d450c75c06d36f0bef9daaa248e040042de97735 100644
--- a/sdk/lib/convert/chunked_conversion.dart
+++ b/sdk/lib/convert/chunked_conversion.dart
@@ -7,6 +7,57 @@ part of dart.convert;
 typedef void _ChunkedConversionCallback<T>(T accumulated);
 
 /**
+ * A converter that supports chunked conversions.
+ *
+ * In addition to immediate conversions from [S] to [T], a chunked converter
+ * also supports longer-running conversions from [S2] to [T2].
+ *
+ * Frequently, the source and target types are the same, but this is not a
+ * requirement. In particular, converters that work with lists in the
+ * immediate conversion, could flatten the type for the chunked conversion.
+ *
+ * For example, the [LineSplitter] class returns a `List<String>` for the
+ * immediate conversion, but returns individual `String`s in the chunked
+ * conversion.
+ */
+abstract class ChunkedConverter<S, T, S2, T2> extends Converter<S, T> {
+
+  const ChunkedConverter();
+
+  /**
+   * Starts a chunked conversion.
+   *
+   * The returned sink serves as input for the long-running conversion. The
+   * given [sink] serves as output.
+   */
+  ChunkedConversionSink<S2> startChunkedConversion(Sink<T2> sink) {
+    throw new UnsupportedError(
+        "This converter does not support chunked conversions: $this");
+  }
+
+  Stream<T2> bind(Stream<S2> stream) {
+    return new Stream<T2>.eventTransformed(
+        stream,
+        (EventSink<T2> sink) =>
+            new _ConverterStreamEventSink<S2, T2>(this, sink));
+  }
+
+  /**
+   * Fuses this instance with the given [other] converter.
+   *
+   * If [other] is a ChunkedConverter (with matching generic types), returns a
+   * [ChunkedConverter].
+   */
+  Converter<S, dynamic> fuse(Converter<T, dynamic> other) {
+    if (other is ChunkedConverter<T, dynamic, T2, dynamic>) {
+      return new _FusedChunkedConverter<S, T, dynamic, S2, T2, dynamic>(
+          this, other);
+    }
+    return super.fuse(other);
+  }
+}
+
+/**
  * A [ChunkedConversionSink] is used to transmit data more efficiently between
  * two converters during chunked conversions.
  *
@@ -55,7 +106,7 @@ class _SimpleCallbackSink<T> extends ChunkedConversionSink<T> {
 }
 
 /**
- * This class converts implements the logic for a chunked conversion as a
+ * This class implements the logic for a chunked conversion as a
  * stream transformer.
  *
  * It is used as strategy in the [EventTransformStream].
@@ -71,9 +122,11 @@ class _ConverterStreamEventSink<S, T> implements EventSink<S> {
    * The input sink for new data. All data that is received with
    * [handleData] is added into this sink.
    */
-  ChunkedConversionSink _chunkedSink;
+  ChunkedConversionSink<S> _chunkedSink;
 
-  _ConverterStreamEventSink(Converter converter, EventSink<T> sink)
+  _ConverterStreamEventSink(
+      Converter/*=ChunkedConverter<dynamic, dynamic, S, T>*/ converter,
+      EventSink<T> sink)
       : this._eventSink = sink,
         _chunkedSink = converter.startChunkedConversion(sink);
 
@@ -83,3 +136,20 @@ class _ConverterStreamEventSink<S, T> implements EventSink<S> {
   }
   void close() => _chunkedSink.close();
 }
+
+/**
+ * Fuses two chunked converters.
+ */
+class _FusedChunkedConverter<S, M, T, S2, M2, T2> extends
+    ChunkedConverter<S, T, S2, T2> {
+  final ChunkedConverter<S, M, S2, M2> _first;
+  final ChunkedConverter<M, T, M2, T2> _second;
+
+  _FusedChunkedConverter(this._first, this._second);
+
+  T convert(S input) => _second.convert(_first.convert(input));
+
+  ChunkedConversionSink<S2> startChunkedConversion(Sink<T2> sink) {
+    return _first.startChunkedConversion(_second.startChunkedConversion(sink));
+  }
+}