[runtime] We don't need an actual instance type for JSIteratorResult.

src/objects.h

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 411 matching lines @@
   V(JS_GLOBAL_PROXY_TYPE)                                       \
   V(JS_ARRAY_TYPE)                                              \
   V(JS_ARRAY_BUFFER_TYPE)                                       \
   V(JS_TYPED_ARRAY_TYPE)                                        \
   V(JS_DATA_VIEW_TYPE)                                          \
   V(JS_PROXY_TYPE)                                              \
   V(JS_SET_TYPE)                                                \
   V(JS_MAP_TYPE)                                                \
   V(JS_SET_ITERATOR_TYPE)                                       \
   V(JS_MAP_ITERATOR_TYPE)                                       \
-  V(JS_ITERATOR_RESULT_TYPE)                                    \
   V(JS_WEAK_MAP_TYPE)                                           \
   V(JS_WEAK_SET_TYPE)                                           \
   V(JS_PROMISE_TYPE)                                            \
   V(JS_REGEXP_TYPE)                                             \
                                                                 \
   V(JS_BOUND_FUNCTION_TYPE)                                     \
   V(JS_FUNCTION_TYPE)                                           \
   V(DEBUG_INFO_TYPE)                                            \
   V(BREAK_POINT_INFO_TYPE)
 
@@ skipping 273 matching lines @@
   JS_GLOBAL_OBJECT_TYPE,
   JS_GLOBAL_PROXY_TYPE,
   JS_ARRAY_TYPE,
   JS_ARRAY_BUFFER_TYPE,
   JS_TYPED_ARRAY_TYPE,
   JS_DATA_VIEW_TYPE,
   JS_SET_TYPE,
   JS_MAP_TYPE,
   JS_SET_ITERATOR_TYPE,
   JS_MAP_ITERATOR_TYPE,
-  JS_ITERATOR_RESULT_TYPE,
   JS_WEAK_MAP_TYPE,
   JS_WEAK_SET_TYPE,
   JS_PROMISE_TYPE,
   JS_REGEXP_TYPE,
   JS_BOUND_FUNCTION_TYPE,
   JS_FUNCTION_TYPE,  // LAST_JS_OBJECT_TYPE, LAST_JS_RECEIVER_TYPE
 
   // Pseudo-types
   FIRST_TYPE = 0x0,
   LAST_TYPE = JS_FUNCTION_TYPE,
@@ skipping 219 matching lines @@
   V(JSArray)                       \
   V(JSArrayBuffer)                 \
   V(JSArrayBufferView)             \
   V(JSTypedArray)                  \
   V(JSDataView)                    \
   V(JSProxy)                       \
   V(JSSet)                         \
   V(JSMap)                         \
   V(JSSetIterator)                 \
   V(JSMapIterator)                 \
-  V(JSIteratorResult)              \
   V(JSWeakCollection)              \
   V(JSWeakMap)                     \
   V(JSWeakSet)                     \
   V(JSRegExp)                      \
   V(HashTable)                     \
   V(Dictionary)                    \
   V(StringTable)                   \
   V(NormalizedMapCache)            \
   V(CompilationCacheTable)         \
   V(CodeCacheHashTable)            \
@@ skipping 1616 matching lines @@
   static const int kValueIndex = 0;
   static const int kWritableIndex = 1;
   static const int kEnumerableIndex = 2;
   static const int kConfigurableIndex = 3;
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSDataPropertyDescriptor);
 };
 
 
+// JSIteratorResult is just a JSObject with a specific initial map.
+// This initial map adds in-object properties for "done" and "value,
+// as specified by ES6 section 25.1.1.3 The IteratorResult Interface
+class JSIteratorResult: public JSObject {

[Yang, 2016/02/08 06:27:13]

do we want to keep the "final" keyword here?

[Benedikt Meurer, 2016/02/08 06:28:22]

Style fix :-)

+ public:
+  // Offsets of object fields.
+  static const int kValueOffset = JSObject::kHeaderSize;
+  static const int kDoneOffset = kValueOffset + kPointerSize;
+  static const int kSize = kDoneOffset + kPointerSize;
+  // Indices of in-object properties.
+  static const int kValueIndex = 0;
+  static const int kDoneIndex = 1;
+
+ private:
+  DISALLOW_IMPLICIT_CONSTRUCTORS(JSIteratorResult);
+};
+
+
 // Common superclass for FixedArrays that allow implementations to share
 // common accessors and some code paths.
 class FixedArrayBase: public HeapObject {
  public:
   // [length]: length of the array.
   inline int length() const;
   inline void set_length(int value);
 
   // Get and set the length using acquire loads and release stores.
   inline int synchronized_length() const;
@@ skipping 7260 matching lines @@
 
  private:
   // Returns the current value of the iterator. This should only be called when
   // |HasMore| returns true.
   inline Object* CurrentValue();
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSMapIterator);
 };
 
 
-// ES6 section 25.1.1.3 The IteratorResult Interface
-class JSIteratorResult final : public JSObject {
- public:
-  // [done]: This is the result status of an iterator next method call.  If the
-  // end of the iterator was reached done is true.  If the end was not reached
-  // done is false and a [value] is available.
-  DECL_ACCESSORS(done, Object)
-
-  // [value]: If [done] is false, this is the current iteration element value.
-  // If [done] is true, this is the return value of the iterator, if it supplied
-  // one.  If the iterator does not have a return value, value is undefined.
-  // In that case, the value property may be absent from the conforming object
-  // if it does not inherit an explicit value property.
-  DECL_ACCESSORS(value, Object)
-
-  // Dispatched behavior.
-  DECLARE_PRINTER(JSIteratorResult)
-  DECLARE_VERIFIER(JSIteratorResult)
-
-  DECLARE_CAST(JSIteratorResult)
-
-  static const int kValueOffset = JSObject::kHeaderSize;
-  static const int kDoneOffset = kValueOffset + kPointerSize;
-  static const int kSize = kDoneOffset + kPointerSize;
-
-  // Indices of in-object properties.
-  static const int kValueIndex = 0;
-  static const int kDoneIndex = 1;
-
- private:
-  DISALLOW_IMPLICIT_CONSTRUCTORS(JSIteratorResult);
-};
-
-
 // Base class for both JSWeakMap and JSWeakSet
 class JSWeakCollection: public JSObject {
  public:
   // [table]: the backing hash table mapping keys to values.
   DECL_ACCESSORS(table, Object)
 
   // [next]: linked list of encountered weak maps during GC.
   DECL_ACCESSORS(next, Object)
 
   static void Initialize(Handle<JSWeakCollection> collection, Isolate* isolate);
@@ skipping 883 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_