Make Exception a class, not an interface, and remove the const constructor.

sdk/lib/core/exceptions.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.
 
 // Exceptions are thrown either by the VM or from Dart code.
 
 /**
- * Interface implemented by all core library exceptions.
+ * Marker interface implemented by all core library exceptions.
  * Defaults to an implementation that only carries a simple message.
  */
-interface Exception default _ExceptionImplementation {
-  // TODO(lrn): This should be an abstract class, but we don't yet support
-  // redirecting factory constructors.
-  const Exception([var message]);
+abstract class Exception  {
+  factory Exception([var message]) => new _ExceptionImplementation(message);
 }
 
 
 /** Default implementation of [Exception] which carries a message. */
 class _ExceptionImplementation implements Exception {
   final message;
   const _ExceptionImplementation([this.message]);
   String toString() => (message == null) ? "Exception" : "Exception: $message";

[floitsch, 2012/11/14 15:43:22]

safeToString?

[Bob Nystrom, 2012/11/14 18:02:39]

Nit, but I would prefer it if "Exception: " were not included in the string. We
have to hack around that manually in pub to give nice user-friendly error
messages:
http://code.google.com/p/dart/source/browse/branches/bleeding_edge/dart/utils...

[Lasse Reichstein Nielsen, 2012/11/16 08:22:49]

It should be a String, but better safe than sorry.

[Lasse Reichstein Nielsen, 2012/11/19 13:18:53]

Seems some tests expect the exact output that we currently have. We should fix
those too eventually, and perhaps use safeToString, but not now.
I moved safeToString to Error, since it seems generally useful. It used to be in
NoSuchMethodError.

 }
 
 
 /**
  * Exception thrown when a string or some other data does not have an expected
  * format and cannot be parsed or processed.
  */
 class FormatException implements Exception {
   /**
    * A message describing the format error.
@@ skipping 42 matching lines @@
 }
 
 /**
  * Exception thrown when a runtime error occurs.
  */
 class RuntimeError implements Exception {
   final message;
   RuntimeError(this.message);
   String toString() => "RuntimeError: $message";
 }