Implement 'as' operator.

corelib/src/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.
  */
 interface Exception default ExceptionImplementation {
@@ skipping 20 matching lines @@
 }
 
 
 /**
  * Exception thrown because of non-existing receiver's method.
  */
 class NoSuchMethodException implements Exception {
   const NoSuchMethodException(Object this._receiver,
                               String this._functionName,
                               List this._arguments,
-                              [List existingArgumentNames = null]) : 
+                              [List existingArgumentNames = null]) :
                                 this._existingArgumentNames = existingArgumentNames;
 
   String toString() {
     StringBuffer sb = new StringBuffer();
     for (int i = 0; i < _arguments.length; i++) {
       if (i > 0) {
         sb.add(", ");
       }
       sb.add(_arguments[i]);
     }
@@ skipping 81 matching lines @@
     }
   }
 
   String get exceptionName() => "NullPointerException";
 
   final String functionName;
   final List arguments;
 }
 
 
+class CastException implements Exception {

[ahe, 2012/06/25 10:36:56]

We generally put fields before constructors which come before methods.

[Lasse Reichstein Nielsen, 2012/06/25 11:20:06]

I know. I was following the convention of the file.

[Lasse Reichstein Nielsen, 2012/06/25 15:16:07]

Ah, to heck with consistency. I'll move them up here.

+  // TODO(lrn): Change expectedType to "Type" when reified types are in.

[ahe, 2012/06/25 10:36:56]

This comment applies to the field below.

[Lasse Reichstein Nielsen, 2012/06/25 11:20:06]

True. I put the comment at the first instance of the name, but it should go
below.

+  CastException(this.actualValue, this.expectedType);
+  String toString() {
+    if (expectedType !== null) {
+      return "$exceptionName : Casting $actualValue to $expectedType";

[ahe, 2012/06/25 10:36:56]

You don't put a space after the exception. The above exceptions are a mess and
needs to be cleaned up. No need to repeat that.

What is actualValue? Is that the object that you're trying to cast? That seems
less helpful than the name of the type that is being cast.

Also, the error message is somewhat indirect. The problem is that $actualValue
is not a subtype of $expectedType.

[Lasse Reichstein Nielsen, 2012/06/25 11:20:06]

The actualValue is the value being cast, yes. As discussed offline, I'll change
it to the actualType instead, and change the message to "Cannot cast $actualType
to $expectedType".
And remove the space.

[Lasse Reichstein Nielsen, 2012/06/25 15:16:07]

I also removed the special casing for when the type wasn't provided. It should
never be necessary to do an explicit cast without an available type.

+    } else {
+      return "$exceptionName : Bad cast of $actualValue";
+    }
+  }
+
+  String get exceptionName() => "CastException";

[ahe, 2012/06/25 10:36:56]

What is this for? Localization doesn't work well with concatenated strings like
above.

[Lasse Reichstein Nielsen, 2012/06/25 11:20:06]

Again I'm following the surrounding code. I assume it is to allow sub-classes to
specialize the name.

[ahe, 2012/06/25 11:57:03]

That the surrounding code is broken is no excuse for copying it.

[Lasse Reichstein Nielsen, 2012/06/25 12:51:10]

I don't think the style guide makes any recommendations about the order of
members in classes. I think being consistent with the surrounding code is more
important than being consistent with code in other files. If the current
ordering isn't good enough, we should reorder the entire file/directory. That'll
be easier if ordering is at least internally consistent.

+
+  final Object actualValue;
+  final Object expectedType;
+}
+
+
 class NoMoreElementsException implements Exception {
   const NoMoreElementsException();
   String toString() => "NoMoreElementsException";
 }
 
 
 class EmptyQueueException implements Exception {
   const EmptyQueueException();
   String toString() => "EmptyQueueException";
 }
@@ skipping 20 matching lines @@
   String toString() => "IllegalJSRegExpException: '$_pattern' '$_errmsg'";
   final String _pattern;
   final String _errmsg;
 }
 
 
 class IntegerDivisionByZeroException implements Exception {
   const IntegerDivisionByZeroException();
   String toString() => "IntegerDivisionByZeroException";
 }