Make _IdentityConverter compatible with Dart SDK 1.x (flutter#18)

Fixes DDC compilation regression introduced by flutter#17

Author: aaronlademann-wf

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 2.1.1
+
+ * Fixed a DDC compilation regression for consumers using the Dart 1.x SDK that was introduced in `2.1.0`.
+
 ## 2.1.0
 
  * Added an `IdentityCodec<T>` which implements `Codec<T,T>` for use as default

lib/src/identity_codec.dart

@@ -1,7 +1,7 @@
 import 'dart:convert';
 
 class _IdentityConverter<T> extends Converter<T, T> {
-  const _IdentityConverter();
+  _IdentityConverter();
   T convert(T input) => input;
 }
 
@@ -17,8 +17,8 @@ class _IdentityConverter<T> extends Converter<T, T> {
 class IdentityCodec<T> extends Codec<T, T> {
   const IdentityCodec();
 
-  Converter<T, T> get decoder => _IdentityConverter<T>();
-  Converter<T, T> get encoder => _IdentityConverter<T>();
+  Converter<T, T> get decoder => new _IdentityConverter<T>();
+  Converter<T, T> get encoder => new _IdentityConverter<T>();
 
   /// Fuse with an other codec.
   ///

pubspec.yaml

@@ -1,5 +1,5 @@
 name: convert
-version: 2.1.0
+version: 2.1.1
 description: Utilities for converting between data representations.
 author: Dart Team <[email protected]>
 homepage: https://github.com/dart-lang/convert