Port of github.com/polymer/polymer.

pkg/polymer/lib/deserialize.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.
+
+library polymer.deserialize;
+
+import 'dart:convert' show JSON;
+import 'dart:mirrors' show reflect, TypeMirror;
+
+final _typeHandlers = () {
+  // TODO(jmesserly): switch to map and symbol literal form when supported.
+  var m = new Map();
+  m[const Symbol('dart.core.String')] = (x, _) => x;
+  m[const Symbol('dart.core.Null')] = (x, _) => x;
+  m[const Symbol('dart.core.DateTime')] = (x, _) {
+    // TODO(jmesserly): shouldn't need to try-catch here
+    // See: https://code.google.com/p/dart/issues/detail?id=1878
+    try {
+      return DateTime.parse(x);
+    } catch (e) {
+      return new DateTime.now();

[blois, 2013/09/27 21:40:52]

not the default value?

[Jennifer Messerly, 2013/09/30 17:44:37]

Yeah, agreed. I filed https://code.google.com/p/dart/issues/detail?id=13666 so
we can collect all of these comments.

+    }
+  };
+  m[const Symbol('dart.core.bool')] = (x, _) => x != 'false';
+  m[const Symbol('dart.core.int')] =
+      (x, def) => int.parse(x, onError: (_) => def);
+  m[const Symbol('dart.core.double')] =
+      (x, def) => double.parse(x, (_) => def);
+  return m;
+}();
+
+/**
+ * Convert representation of [value] based on type of [defaultValue].
+ */
+Object deserializeValue(String value, Object defaultValue, TypeMirror type) {
+  var handler = _typeHandlers[type.qualifiedName];

[blois, 2013/09/27 21:40:52]

Is this extensible? What would it take for someone to add a Color deserializer?

[Jennifer Messerly, 2013/09/30 17:44:37]

agreed, added to #13666

+  if (handler != null) return handler(value, defaultValue);
+
+  try {
+    // If the string is an object, we can parse is with the JSON library.
+    // include convenience replace for single-quotes. If the author omits
+    // quotes altogether, parse will fail.
+    return JSON.decode(value.replaceAll("'", '"'));
+
+    // TODO(jmesserly): deserialized JSON is not assignable to most objects in
+    // Dart. We should attempt to convert it appropriately.
+  } catch(e) {
+    // The object isn't valid JSON, return the raw value
+    return value;
+  }
+}