Change Hash subclasses to be Converters.

lib/src/digest_sink.dart

Index: lib/src/digest_sink.dart
diff --git a/lib/src/digest_sink.dart b/lib/src/digest_sink.dart
new file mode 100644
index 0000000000000000000000000000000000000000..0b24a51585c618584c9f3e28870142f8e97eb983
--- /dev/null
+++ b/lib/src/digest_sink.dart
@@ -0,0 +1,26 @@
+// 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.
+
+library crypto.digest_sink;
+
+import 'digest.dart';
+
+/// A sink used to get a digest value out of [Hash.startChunkedConversion].
+class DigestSink extends Sink<Digest> {
+  /// The value added to the sink, if any.
+  Digest get value {
+    assert(_value != null);
+    return _value;
+  }
+  Digest _value;
+
+  void add(Digest value) {

[Bob Nystrom, 2015/09/22 17:47:31]

Document that this can only be called once.

[nweiz, 2015/09/22 21:37:33]

Done.

+    assert(_value == null);
+    _value = value;
+  }
+
+  void close() {
+    assert(_value != null);
+  }
+}