Use the distinguished class, ApiFailure, to signal when a Dart_Result is

runtime/vm/object.h

 // Copyright (c) 2011, 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "vm/assert.h"
 #include "vm/dart.h"
 #include "vm/globals.h"
@@ skipping 121 matching lines @@
     kTokenStreamClass,
     kScriptClass,
     kLibraryClass,
     kLibraryPrefixClass,
     kCodeClass,
     kInstructionsClass,
     kPcDescriptorsClass,
     kExceptionHandlersClass,
     kContextClass,
     kContextScopeClass,
+    kApiFailureClass,
     kMaxId,
     kInvalidIndex = -1,
   };
 
   virtual ~Object() { }
 
   RawObject* raw() const { return raw_; }
   void operator=(RawObject* value) { SetRaw(value); }
 
   inline RawClass* clazz() const;
@@ skipping 79 matching lines @@
   static RawClass* library_class() { return library_class_; }
   static RawClass* library_prefix_class() { return library_prefix_class_; }
   static RawClass* code_class() { return code_class_; }
   static RawClass* instructions_class() { return instructions_class_; }
   static RawClass* pc_descriptors_class() { return pc_descriptors_class_; }
   static RawClass* exception_handlers_class() {
     return exception_handlers_class_;
   }
   static RawClass* context_class() { return context_class_; }
   static RawClass* context_scope_class() { return context_scope_class_; }
+  static RawClass* api_failure_class() { return api_failure_class_; }
 
   static int GetSingletonClassIndex(const RawClass* raw_class);
   static RawClass* GetSingletonClass(int index);
   static const char* GetSingletonClassName(int index);
 
   static void Init(Isolate* isolate);
   static void InitFromSnapshot(Isolate* isolate);
   static void InitOnce();
 
   static intptr_t InstanceSize() {
@@ skipping 72 matching lines @@
   static RawClass* token_stream_class_;  // Class of the TokenStream vm object.
   static RawClass* script_class_;  // Class of the Script vm object.
   static RawClass* library_class_;  // Class of the Library vm object.
   static RawClass* library_prefix_class_;  // Class of Library prefix vm object.
   static RawClass* code_class_;  // Class of the Code vm object.
   static RawClass* instructions_class_;  // Class of the Instructions vm object.
   static RawClass* pc_descriptors_class_;  // Class of PcDescriptors vm object.
   static RawClass* exception_handlers_class_;  // Class of ExceptionHandlers.
   static RawClass* context_class_;  // Class of the Context vm object.
   static RawClass* context_scope_class_;  // Class of ContextScope vm object.
+  static RawClass* api_failure_class_;  // Class of ApiFailure.
 
   friend class Class;
 
   // Disallow allocation.
   void* operator new(size_t size);
   // Disallow copy constructor.
   DISALLOW_COPY_AND_ASSIGN(Object);
 };
 
 
@@ skipping 1600 matching lines @@
 
  private:
   void set_exception(const Instance& exception) const;
   void set_stacktrace(const Instance& stacktrace) const;
 
   HEAP_OBJECT_IMPLEMENTATION(UnhandledException, Object);
   friend class Class;
 };
 
 
+class ApiFailure : public Object {
+ public:
+  RawString* message() const { return raw_ptr()->message_; }
+  static intptr_t message_offset() {
+    return OFFSET_OF(RawApiFailure, message_);
+  }
+
+  static intptr_t InstanceSize() {
+    return RoundedAllocationSize(sizeof(RawApiFailure));
+  }
+
+  static RawApiFailure* New(const String& message,
+                            Heap::Space space = Heap::kNew);
+
+ private:
+  void set_message(const String& message) const;
+
+  HEAP_OBJECT_IMPLEMENTATION(ApiFailure, Object);
+  friend class Class;
+};
+
+
 // Instance is the base class for all instance objects (aka the Object class
 // in Dart source code.
 class Instance : public Object {
  public:
   virtual bool Equals(const Instance& other) const;
   virtual RawInstance* Canonicalize() const;
 
   RawObject* GetField(const Field& field) const {
     return *FieldAddr(field);
   }
@@ skipping 880 matching lines @@
 }
 
 
 void Context::SetAt(intptr_t index, const Instance& value) const {
   StorePointer(InstanceAddr(index), value.raw());
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_