Add a hexadecimal codec.

lib/src/hex.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.
+
+library convert.hex;
+
+import 'dart:convert';
+
+import 'hex/encoder.dart';
+import 'hex/decoder.dart';
+
+export 'hex/encoder.dart' hide hexEncoder;
+export 'hex/decoder.dart' hide hexDecoder;
+
+/// The canonical instance of [HexCodec].
+const hex = const HexCodec._();
+
+/// A codec that converts byte arrays to and from hexadecimal strings.
+///
+/// This should be used via the [hex] field.
+class HexCodec extends Codec<List<int>, String> {
+  final HexEncoder encoder = hexEncoder;

[Lasse Reichstein Nielsen, 2015/09/23 08:32:03]

I'd make these getters that return the encode/decoder instead of instance
fields. 

[nweiz, 2015/09/23 22:04:20]

Done.

+  final HexDecoder decoder = hexDecoder;
+
+  const HexCodec._();
+}