Create specific null read only handles for the frequently used types

runtime/vm/object.h

 // 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.
 
 #ifndef VM_OBJECT_H_
 #define VM_OBJECT_H_
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/utils.h"
@@ skipping 99 matching lines @@
     ASSERT(obj.Is##object());                                                  \
     return reinterpret_cast<const object&>(obj);                               \
   }                                                                            \
   static Raw##object* RawCast(RawObject* raw) {                                \
     ASSERT(Object::Handle(raw).Is##object());                                  \
     return reinterpret_cast<Raw##object*>(raw);                                \
   }                                                                            \
   static Raw##object* null() {                                                 \
     return reinterpret_cast<Raw##object*>(Object::null());                     \
   }                                                                            \
-  static const object& null_object() {                                         \
-    return reinterpret_cast<const object&>(Object::null_object());             \
-  }                                                                            \
   virtual const char* ToCString() const;                                       \
   static const ClassId kClassId = k##object##Cid;                              \
  private:  /* NOLINT */                                                        \
   /* Initialize the handle based on the raw_ptr in the presence of null. */    \
   static void initializeHandle(object* obj, RawObject* raw_ptr) {              \
     if (raw_ptr != Object::null()) {                                           \
       obj->SetRaw(raw_ptr);                                                    \
     } else {                                                                   \
       obj->raw_ = Object::null();                                              \
       object fake_object;                                                      \
@@ skipping 143 matching lines @@
 
   bool IsNotTemporaryScopedHandle() const;
 
   static RawObject* Clone(const Object& src, Heap::Space space = Heap::kNew);
 
   static Object& Handle(Isolate* isolate, RawObject* raw_ptr) {
     Object* obj = reinterpret_cast<Object*>(VMHandles::AllocateHandle(isolate));
     initializeHandle(obj, raw_ptr);
     return *obj;
   }
+  static Object* ReadOnlyHandle() {
+    Object* obj = reinterpret_cast<Object*>(
+        Dart::AllocateReadOnlyHandle());
+    initializeHandle(obj, Object::null());
+    return obj;
+  }
 
   static Object& Handle() {
     return Handle(Isolate::Current(), null_);
   }
 
   static Object& Handle(Isolate* isolate) {
     return Handle(isolate, null_);
   }
 
   static Object& Handle(RawObject* raw_ptr) {
@@ skipping 13 matching lines @@
 
   static Object& ZoneHandle(RawObject* raw_ptr) {
     return ZoneHandle(Isolate::Current(), raw_ptr);
   }
 
   static RawObject* null() { return null_; }
   static const Object& null_object() {
     ASSERT(null_object_ != NULL);
     return *null_object_;
   }
+  static const Array& null_array() {
+    ASSERT(null_array_ != NULL);
+    return *null_array_;
+  }
+  static const String& null_string() {
+    ASSERT(null_string_ != NULL);
+    return *null_string_;
+  }
+  static const Instance& null_instance() {
+    ASSERT(null_instance_ != NULL);
+    return *null_instance_;
+  }
+  static const AbstractTypeArguments& null_abstract_type_arguments() {
+    ASSERT(null_abstract_type_arguments_ != NULL);
+    return *null_abstract_type_arguments_;
+  }
   static const Array& empty_array() {
     ASSERT(empty_array_ != NULL);
     return *empty_array_;
   }
 
   // The sentinel is a value that cannot be produced by Dart code.
   // It can be used to mark special values, for example to distinguish
   // "uninitialized" fields.
   static const Instance& sentinel() {
     ASSERT(sentinel_ != NULL);
@@ skipping 214 matching lines @@
   static RawClass* megamorphic_cache_class_;  // Class of MegamorphiCache.
   static RawClass* subtypetestcache_class_;  // Class of SubtypeTestCache.
   static RawClass* api_error_class_;  // Class of ApiError.
   static RawClass* language_error_class_;  // Class of LanguageError.
   static RawClass* unhandled_exception_class_;  // Class of UnhandledException.
   static RawClass* unwind_error_class_;  // Class of UnwindError.
 
   // The static values below are read-only handle pointers for singleton
   // objects that are shared between the different isolates.
   static Object* null_object_;
+  static Array* null_array_;
+  static String* null_string_;
+  static Instance* null_instance_;
+  static AbstractTypeArguments* null_abstract_type_arguments_;
   static Array* empty_array_;
   static Instance* sentinel_;
   static Instance* transition_sentinel_;
   static Instance* unknown_constant_;
   static Instance* non_constant_;
   static Bool* bool_true_;
   static Bool* bool_false_;
   static Smi* smi_illegal_cid_;
   static LanguageError* snapshot_writer_error_;
 
@@ skipping 5277 matching lines @@
 
 
 RawObject* MegamorphicCache::GetTargetFunction(const Array& array,
                                                intptr_t index) {
   return array.At((index * kEntryLength) + kTargetFunctionIndex);
 }
 
 }  // namespace dart
 
 #endif  // VM_OBJECT_H_