pkg/serialization: add format param to Serialization.read method

pkg/serialization/lib/serialization.dart

 // Copyright (c) 2012, 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.
 
 /**
  * This provides a general-purpose serialization facility for Dart objects. A
  * [Serialization] is defined in terms of [SerializationRule]s and supports
  * reading and writing to different formats.
  *
  * ## Installing ##
@@ skipping 343 matching lines @@
   void addRule(SerializationRule rule) {
     rule.number = rules.length;
     rules.add(rule);
   }
 
   /**
    * This writes out an object graph rooted at [object] and returns the result.
    * The [format] parameter determines the form of the result. The default
    * format returns a String in [json] format.
    */
-  write(Object object, [Format format]) {
+  write(Object object, {Format format}) {
     return newWriter(format).write(object);
   }
 
   /**
    * Return a new [Writer] object for this serialization. This is useful if you
    * want to do something more complex with the writer than just returning
    * the final result.
    */
-  Writer newWriter([Format format]) =>
-      new Writer(this, format);
+  Writer newWriter([Format format]) => new Writer(this, format);
 
   /**
    * Read the serialized data from [input] and return the root object
    * from the result. The [input] can be of any type that the [Format]
    * reads/writes, but normally will be a [List], [Map], or a simple type.
+   * The [format] parameter determines the form of the result. The default
+   * format returns a String in [json] format.
    * If there are objects that need to be resolved
    * in the current context, they should be provided in [externals] as a
    * Map from names to values. In particular, in the current implementation
    * any class mirrors needed should be provided in [externals] using the
    * class name as a key. In addition to the [externals] map provided here,
    * values will be looked up in the [namedObjects] map.
    */
-  read(input, [Map externals = const {}]) {
-    return newReader().read(input, externals);
+  read(input, {Format format, Map externals: const {}}) {
+    return newReader(format).read(input, externals);
   }
 
   /**
    * Return a new [Reader] object for this serialization. This is useful if
    * you want to do something more complex with the reader than just returning
    * the final result.
    */
   Reader newReader([Format format]) => new Reader(this, format);
 
   /**
@@ skipping 94 matching lines @@
     }
     return ifAbsent == null ? null : ifAbsent();
   }
 }
 
 /**
  * An exception class for errors during serialization.
  */
 class SerializationException implements Exception {
   final String message;
-  const SerializationException([this.message]);
-  toString() => "SerializationException($message)";
+  const SerializationException(this.message);
+  String toString() => "SerializationException($message)";
 }