Second round of cleanups for new optional parameter semantics.

pkg/args/lib/args.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 library lets you define parsers for parsing raw command-line arguments
  * into a set of options and values using [GNU][] and [POSIX][] style options.
  *
  * ## Defining options ##
  *
@@ skipping 224 matching lines @@
     _addOption(name, abbr, help, null, null, defaultsTo, callback,
         isFlag: true, negatable: negatable);
   }
 
   /**
    * Defines a value-taking option. Throws an [ArgumentError] if:
    *
    * * There is already an option with name [name].
    * * There is already an option using abbreviation [abbr].
    */
-  void addOption(String name, [String abbr, String help, List<String> allowed,
+  void addOption(String name, {String abbr, String help, List<String> allowed,
       Map<String, String> allowedHelp, String defaultsTo,
-      void callback(value), bool allowMultiple = false]) {
+      void callback(value), bool allowMultiple: false}) {
     _addOption(name, abbr, help, allowed, allowedHelp, defaultsTo,
         callback, isFlag: false, allowMultiple: allowMultiple);
   }
 
   void _addOption(String name, String abbr, String help, List<String> allowed,
       Map<String, String> allowedHelp, defaultsTo,
       void callback(value), {bool isFlag, bool negatable: false,
       bool allowMultiple: false}) {
     // Make sure the name isn't in use.
     if (_options.containsKey(name)) {
@@ skipping 518 matching lines @@
       allowedBuffer.add(allowed);
       if (allowed == option.defaultValue) {
         allowedBuffer.add(' (default)');
       }
       first = false;
     }
     allowedBuffer.add(']');
     return allowedBuffer.toString();
   }
 }