Wrote functions to convert collections and maps to strings and invoked

corelib/src/implementation/maps.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 /*
  * Helper class which implements complex [Map] operations
  * in term of basic ones ([Map.getKeys], [Map.operator []],
  * [Map.operator []=] and [Map.remove].)  Not all methods are
  * necessary to implement each particular operation.
  */
 class Maps {
@@ skipping 40 matching lines @@
     final result = [];
     for (final k in map.getKeys()) {
       result.add(map[k]);
     }
     return result;
   }
 
   static int length(Map map) => map.getKeys().length;
 
   static bool isEmpty(Map map) => length(map) == 0;
+
+  /**
+   * Returns a string representing the specified map. The returned string
+   * looks like this: [:"{key0: value0, key1: value1, ... keyN: valueN}":].
+   * The value returned by its [toString] method is used to represent each
+   * key or value.
+   *
+   * If the map collection contains a reference to itself, either
+   * directly as a key or value, or indirectly through other collections
+   * or maps, the contained reference is rendered as [:"{...}":]. This
+   * prevents the infinite regress that would otherwise occur. So, for example,
+   * calling this method on a map whose sole entry maps the string key "me"
+   * to a reference to the map would return [:"{me: {...}}":].
+   *
+   * A typical implementation of a map's [toString] method will
+   * simply return the results of this method applied to the collection.
+   */
+  static String mapToString(Map m) {
+    var result = new StringBuffer();
+    _emitMap(m, result, new List());
+    return result.toString();
+  }
+
+  /**
+   * Appends a string representing the specified map to the specified
+   * string buffer. The string is formatted as per [mapToString].
+   * The [:visiting:] list contains references to all of the enclosing
+   * collections and maps (which are currently in the process of being
+   * emitted into [:result:]). The [:visiting:] parameter allows this method
+   * to generate a [:"[...]":] or [:"{...}":] where required. In other words,
+   * it allows this method and [_emitCollection] to identify recursive maps
+   * and collections.
+   */
+  static void _emitMap(Map m, StringBuffer result, List visiting) {
+    visiting.add(m);
+    result.add("{");

[Bob Nystrom, 2012/02/06 18:23:17]

Either way is OK, but we generally default to single-quoted stings unless the
string happens to contain an apostrophe.

[jjb, 2012/02/06 19:10:03]

Interesting!  This is the opposite of what I'm used to from many other "curly
braces languages." Given that we're trying to appeal to JavaScript and Java
programmers, have we made the right choice?  If so, should we make this clear in
your style guide (http://www.dartlang.org/articles/idiomatic-dart)?

[Bob Nystrom, 2012/02/06 20:37:12]

I think so. We find that we very frequently have HTML inside string literals and
want to use double quotes for attributes. That's easy if you're in the habit of
using single quotes for your strings:  '<div class="blah">'.

That being said, I find it easy to trip up when using contractions: 'this isn't
right'.
I've got a note on my todo-list to add that. It isn't a huge priority (because
it's a pretty slight preference for single-quoted strings) but if I get a
chance, I'll probably add it.

[Ivan Posva, 2012/02/15 09:54:10]

I think the choice is really personal preference. As noted below there are
stumbling blocks with both defaults. The resolution of a project wide preference
should not block this change.

+
+    bool first = true;
+    m.forEach((k, v) {
+      if (!first) {
+        result.add(", ");
+      }
+      first = false;
+      Collections._emitObject(k, result, visiting);
+      result.add(": ");
+      Collections._emitObject(v, result, visiting);
+    });
+
+    result.add("}");
+    visiting.removeLast();
+  }
 }