Implement 'as' operator.

lib/compiler/implementation/lib/js_helper.dart

Index: lib/compiler/implementation/lib/js_helper.dart
diff --git a/lib/compiler/implementation/lib/js_helper.dart b/lib/compiler/implementation/lib/js_helper.dart
index a7b2f06a280802240ec6c0f0e40707368b3c3077..a7322c040cef705ad3cbc17f44015ad8389e5061 100644
--- a/lib/compiler/implementation/lib/js_helper.dart
+++ b/lib/compiler/implementation/lib/js_helper.dart
@@ -978,8 +978,8 @@ getRuntimeTypeInfo(target) {
 
 /**
  * The following methods are called by the runtime to implement
- * checked mode. We specialize each primitive type (eg int, bool), and
- * use the compiler's convention to do is checks on regular objects.
+ * checked mode and casts. We specialize each primitive type (eg int, bool), and
+ * use the compiler's convention to do is-checks on regular objects.
  */
 stringTypeCheck(value) {
   if (value === null) return value;
@@ -987,42 +987,78 @@ stringTypeCheck(value) {
   throw new TypeError('$value does not implement String');
 }
 
+stringTypeCast(value) {
+  if (value is String || value === null) return value;
+  throw new CastException(value, 'String');
+}
+
 doubleTypeCheck(value) {
   if (value === null) return value;
   if (value is double) return value;
   throw new TypeError('$value does not implement double');
 }
 
+doubleTypeCast(value) {
+  if (value is double || value === null) return value;
+  throw new CastException(value, 'double');
+}
+
 numTypeCheck(value) {
   if (value === null) return value;
   if (value is num) return value;
   throw new TypeError('$value does not implement num');
 }
 
+numTypeCast(value) {
+  if (value is num || value === null) return value;
+  throw new CastException(value, 'num');
+}
+
 boolTypeCheck(value) {
   if (value === null) return value;
   if (value is bool) return value;
   throw new TypeError('$value does not implement bool');
 }
 
+boolTypeCast(value) {
+  if (value is bool || value === null) return value;
+  throw new CastException(value, 'bool');
+}
+
 functionTypeCheck(value) {
   if (value === null) return value;
   if (value is Function) return value;
   throw new TypeError('$value does not implement Function');
 }
 
+functionTypeCast(value) {
+  if (value is Function || value === null) return value;
+  throw new CastException(value, 'Function');
+}
+
 intTypeCheck(value) {
   if (value === null) return value;
   if (value is int) return value;
   throw new TypeError('$value does not implement int');
 }
 
+intTypeCast(value) {
+  if (value is int || value === null) return value;
+  throw new CastException(value, 'int');
+}
+
 void propertyTypeError(value, property) {
   // Cuts the property name to the class name.
   String name = property.substring(3, property.length);
   throw new TypeError('$value does not implement $name');
 }
 
+void propertyTypeCastError(value, property) {
+  // Cuts the property name to the class name.
+  String name = property.substring(3, property.length);
+  throw new CastException(value, name);
+}
+
 /**
  * For types that are not supertypes of native (eg DOM) types,
  * we emit a simple property check to check that an object implements
@@ -1034,6 +1070,11 @@ propertyTypeCheck(value, property) {
   propertyTypeError(value, property);
 }
 
+propertyTypeCast(Object value, Object property) {

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

Remove types from signature.

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

Why?

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

Why are they there?

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

For the same reasons we use them everywhere else (except, apparently, this file,
which I hear is not a reason to follow suit) - to document the expected argument
types.
I'm aware that using "Object" as opposed to "var" (or nothing) will not make a
difference in checked mode, but it will document that this code doesn't expect
any other properties of the arguments.

I should add a "void" return too.

[ahe, 2012/06/25 12:56:32]

Generally, you shouldn't use Object unless you're absolutely sure that is what
you mean. In this case it is not correct. Only String is a valid argument for
the second argument.
I would agree if it was correct that you only expected Object's properties.
That would be incorrect.

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

Ack, I agree.
There is no good type to use here.

+  if (value === null || JS('bool', '!!#[#]', value, property)) return value;
+  propertyTypeCastError(value, property);
+}
+
 /**
  * For types that are supertypes of native (eg DOM) types, we emit a
  * call because we cannot add a JS property to their prototype at load
@@ -1048,6 +1089,15 @@ callTypeCheck(value, property) {
   propertyTypeError(value, property);
 }
 
+callTypeCast(value, property) {

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

A comment would be nice here.

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

Will do.

+  if (value === null
+      || ((JS('bool', 'typeof # === "object"', value))
+          && JS('bool', '#[#]()', value, property))) {
+    return value;
+  }
+  propertyTypeCastError(value, property);
+}
+
 /**
  * Specialization of the type check for String and its supertype
  * since [value] can be a JS primitive.
@@ -1059,6 +1109,12 @@ stringSuperTypeCheck(value, property) {
   propertyTypeError(value, property);
 }
 
+stringSuperTypeCast(value, property) {
+  if (value is String || value === null) return value;
+  if (JS('bool', '!!#[#]', value, property)) return value;

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

This could be: return propertyTypeCast(value, property);

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

Well spotted.

+  propertyTypeCastError(value, property);
+}
+
 stringSuperNativeTypeCheck(value, property) {
   if (value === null) return value;
   if (value is String) return value;
@@ -1066,6 +1122,12 @@ stringSuperNativeTypeCheck(value, property) {
   propertyTypeError(value, property);
 }
 
+stringSuperNativeTypeCast(value, property) {
+  if (value is String || value === null) return value;
+  if (JS('bool', '#[#]()', value, property)) return value;

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

Should this call callTypeCast?

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

Don't you need to check for typeof value === 'object'?

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

I think it should follow the tringSuperNativeTypeCheck above. I don't claim to
understand what it does.

+  propertyTypeCastError(value, property);
+}
+
 /**
  * Specialization of the type check for List and its supertypes,
  * since [value] can be a JS array.
@@ -1076,6 +1138,11 @@ listTypeCheck(value) {
   throw new TypeError('$value does not implement List');
 }
 
+listTypeCast(value) {
+  if (value is List || value === null) return value;
+  throw new CastException(value, 'List');
+}
+
 listSuperTypeCheck(value, property) {
   if (value === null) return value;
   if (value is List) return value;
@@ -1083,6 +1150,12 @@ listSuperTypeCheck(value, property) {
   propertyTypeError(value, property);
 }
 
+listSuperTypeCast(value, property) {
+  if (value is List || value === null) return value;
+  if (JS('bool', '!!#[#]', value, property)) return value;

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

Call propertyTypeCast?

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

Will do.

+  propertyTypeCastError(value, property);
+}
+
 listSuperNativeTypeCheck(value, property) {
   if (value === null) return value;
   if (value is List) return value;
@@ -1090,6 +1163,12 @@ listSuperNativeTypeCheck(value, property) {
   propertyTypeError(value, property);
 }
 
+listSuperNativeTypeCast(value, property) {
+  if (value is List || value === null) return value;
+  if (JS('bool', '#[#]()', value, property)) return value;

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

Call callTypeCast?

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

That should work. And ditto for the check.

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

Actually, the "callTypeCast" does more tests than what we do here, so I'll just
change the ones that can be propertyTypeCast.

+  propertyTypeCastError(value, property);
+}
+
 /**
  * Special interface recognized by the compiler and implemented by DOM
  * objects that support integer indexing. This interface is not