Implement 'as' operator.

corelib/src/exceptions.dart

Index: corelib/src/exceptions.dart
diff --git a/corelib/src/exceptions.dart b/corelib/src/exceptions.dart
index 3e95797999cb3a90cce1e2ea8a3e4cd1c8b00e35..da213b6cd7007b1f2dbda6dfc7755acc600af542 100644
--- a/corelib/src/exceptions.dart
+++ b/corelib/src/exceptions.dart
@@ -38,7 +38,7 @@ 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() {
@@ -140,6 +140,24 @@ class NullPointerException implements Exception {
 }
 
 
+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";