Make JSON encoder take extra function argument to use instead of toJson calls.

sdk/lib/json/json.dart

Index: sdk/lib/json/json.dart
diff --git a/sdk/lib/json/json.dart b/sdk/lib/json/json.dart
index 8bd8ab215ebf6e72b5b6ecba08cbfe5bf9f97687..8cbf28bef21cf9fa17c080cd81870962643ad7e2 100644
--- a/sdk/lib/json/json.dart
+++ b/sdk/lib/json/json.dart
@@ -9,6 +9,7 @@
 library dart.json;
 
 import "dart:convert";
+import "dart:collection" show HashSet;
 export "dart:convert" show JsonUnsupportedObjectError, JsonCyclicError;
 
 // JSON parsing and serialization.
@@ -44,27 +45,30 @@ parse(String json, [reviver(var key, var value)]) {
  * For [List], the elements must all be serializable.
  * For [Map], the keys must be [String] and the values must be serializable.
  *
- * If a value is any other type is attempted serialized, a "toJson()" method
- * is invoked on the object and the result, which must be a directly
- * serializable value, is serialized instead of the original value.
+ * If a value is any other type is attempted serialized, the [convert] method
+ * is called with the object as argument, and the result, which must be a
+ * directly serializable value, is serialized instead of the original value.
+ * If [convert] is omitted, the default is to call `object.toJson()` on the
+ * object.
  *
- * If the object does not support this method, throws, or returns a
- * value that is not directly serializable, a [JsonUnsupportedObjectError]
- * exception is thrown. If the call throws (including the case where there
- * is no nullary "toJson" method, the error is caught and stored in the
+ * If the conversion throws, or returns a value that is not directly
+ * serializable, a [JsonUnsupportedObjectError] exception is thrown.
+ * If the call throws (including the case where there
+ * is no nullary "toJson" method), the error is caught and stored in the
  * [JsonUnsupportedObjectError]'s [:cause:] field.
  *
  * If a [List] or [Map] contains a reference to itself, directly or through
  * other lists or maps, it cannot be serialized and a [JsonCyclicError] is
  * thrown.
  *
- * Json Objects should not change during serialization.
+ * The objects being serialized should not change during serialization.
  * If an object is serialized more than once, [stringify] is allowed to cache
  * the JSON text for it. I.e., if an object changes after it is first
  * serialized, the new values may or may not be reflected in the result.
  */
-String stringify(Object object) {
-  return _JsonStringifier.stringify(object);
+String stringify(Object object, [convert(object)]) {

[floitsch, 2013/10/04 15:25:08]

You don't have the latest version (which now has deprecation notices).

But you should copy your changes into the json-package.

[Lasse Reichstein Nielsen, 2013/10/07 12:46:59]

Merging .... please hold. :)

I don't want to support the json package with new functionality.
We moved it to a package in case someone was using it, but that was mainly for
the custom parser, not the stringifier. Eventually we could make the stringifier
in pkg/json use the convert library instead.

I changed the lib/json version because that's the one we use in convert, and the
one we'll eventually move into the convert library when we drop the json
library.

New users of the json library at this time will know it's deprecated, and can
use the convert library instead.

+  if (convert == null) convert = _defaultConvert;
+  return _JsonStringifier.stringify(object, convert);
 }
 
 /**
@@ -76,8 +80,9 @@ String stringify(Object object) {
  * If serialization fails by throwing, some data might have been added to
  * [output], but it won't contain valid JSON text.
  */
-void printOn(Object object, StringSink output) {
-  return _JsonStringifier.printOn(object, output);
+void printOn(Object object, StringSink output, [ convert(object) ]) {
+  if (convert == null) convert = _defaultConvert;
+  return _JsonStringifier.printOn(object, output, convert);
 }
 
 //// Implementation ///////////////////////////////////////////////////////////
@@ -623,22 +628,25 @@ class JsonParser {
   }
 }
 
+Object _defaultConvert(object) => object.toJson();
 
 class _JsonStringifier {
-  StringSink sink;
-  List<Object> seen;  // TODO: that should be identity set.
+  final Function converter;
+  final StringSink sink;
+  final Set<Object> seen;
 
-  _JsonStringifier(this.sink) : seen = [];
+  _JsonStringifier(this.sink, this.converter)
+      : this.seen = new HashSet.identity();
 
-  static String stringify(final object) {
+  static String stringify(final object, convert(object)) {
     StringBuffer output = new StringBuffer();
-    _JsonStringifier stringifier = new _JsonStringifier(output);
+    _JsonStringifier stringifier = new _JsonStringifier(output, convert);
     stringifier.stringifyValue(object);
     return output.toString();
   }
 
-  static void printOn(final object, StringSink output) {
-    _JsonStringifier stringifier = new _JsonStringifier(output);
+  static void printOn(final object, StringSink output, convert(object)) {
+    _JsonStringifier stringifier = new _JsonStringifier(output, convert);
     stringifier.stringifyValue(object);
   }
 
@@ -695,11 +703,8 @@ class _JsonStringifier {
   }
 
   void checkCycle(final object) {
-    // TODO: use Iterables.
-    for (int i = 0; i < seen.length; i++) {
-      if (identical(seen[i], object)) {
-        throw new JsonCyclicError(object);
-      }
+    if (seen.contains(object)) {
+      throw new JsonCyclicError(object);
     }
     seen.add(object);
   }
@@ -711,11 +716,11 @@ class _JsonStringifier {
     if (!stringifyJsonValue(object)) {
       checkCycle(object);
       try {
-        var customJson = object.toJson();
+        var customJson = converter(object);
         if (!stringifyJsonValue(customJson)) {
           throw new JsonUnsupportedObjectError(object);
         }
-        seen.removeLast();
+        seen.remove(object);
       } catch (e) {
         throw new JsonUnsupportedObjectError(object, cause: e);
       }
@@ -760,7 +765,7 @@ class _JsonStringifier {
         }
       }
       sink.write(']');
-      seen.removeLast();
+      seen.remove(object);
       return true;
     } else if (object is Map) {
       checkCycle(object);
@@ -779,7 +784,7 @@ class _JsonStringifier {
         first = false;
       });
       sink.write('}');
-      seen.removeLast();
+      seen.remove(object);
       return true;
     } else {
       return false;