1 files changed, 120 insertions, 0 deletions
diff --git a/deps/v8/src/maybe-handles.h b/deps/v8/src/maybe-handles.h
new file mode 100644
index 00000000000..d4b639e18ea
--- /dev/null
+++ b/deps/v8/src/maybe-handles.h
@@ -0,0 +1,120 @@
+// Copyright 2011 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_MAYBE_HANDLES_H_
+#define V8_MAYBE_HANDLES_H_
+
+#include <type_traits>
+
+#include "src/handles.h"
+
+namespace v8 {
+namespace internal {
+
+// ----------------------------------------------------------------------------
+// A Handle can be converted into a MaybeHandle. Converting a MaybeHandle
+// into a Handle requires checking that it does not point to nullptr.  This
+// ensures nullptr checks before use.
+//
+// Also note that Handles do not provide default equality comparison or hashing
+// operators on purpose. Such operators would be misleading, because intended
+// semantics is ambiguous between Handle location and object identity.
+template <typename T>
+class MaybeHandle final {
+ public:
+  V8_INLINE MaybeHandle() {}
+
+  // Constructor for handling automatic up casting from Handle.
+  // Ex. Handle<JSArray> can be passed when MaybeHandle<Object> is expected.
+  template <typename S, typename = typename std::enable_if<
+                            std::is_convertible<S*, T*>::value>::type>
+  V8_INLINE MaybeHandle(Handle<S> handle)
+      : location_(reinterpret_cast<T**>(handle.location_)) {}
+
+  // Constructor for handling automatic up casting.
+  // Ex. MaybeHandle<JSArray> can be passed when Handle<Object> is expected.
+  template <typename S, typename = typename std::enable_if<
+                            std::is_convertible<S*, T*>::value>::type>
+  V8_INLINE MaybeHandle(MaybeHandle<S> maybe_handle)
+      : location_(reinterpret_cast<T**>(maybe_handle.location_)) {}
+
+  V8_INLINE MaybeHandle(T* object, Isolate* isolate);
+
+  V8_INLINE void Assert() const { DCHECK_NOT_NULL(location_); }
+  V8_INLINE void Check() const { CHECK_NOT_NULL(location_); }
+
+  V8_INLINE Handle<T> ToHandleChecked() const {
+    Check();
+    return Handle<T>(location_);
+  }
+
+  // Convert to a Handle with a type that can be upcasted to.
+  template <typename S>
+  V8_INLINE bool ToHandle(Handle<S>* out) const {
+    if (location_ == nullptr) {
+      *out = Handle<T>::null();
+      return false;
+    } else {
+      *out = Handle<T>(location_);
+      return true;
+    }
+  }
+
+  // Returns the raw address where this handle is stored. This should only be
+  // used for hashing handles; do not ever try to dereference it.
+  V8_INLINE Address address() const { return bit_cast<Address>(location_); }
+
+  bool is_null() const { return location_ == nullptr; }
+
+ protected:
+  T** location_ = nullptr;
+
+  // MaybeHandles of different classes are allowed to access each
+  // other's location_.
+  template <typename>
+  friend class MaybeHandle;
+};
+
+// A handle which contains a potentially weak pointer. Keeps it alive (strongly)
+// while the MaybeObjectHandle is alive.
+class MaybeObjectHandle {
+ public:
+  inline MaybeObjectHandle();
+  inline MaybeObjectHandle(MaybeObject* object, Isolate* isolate);
+  inline MaybeObjectHandle(Object* object, Isolate* isolate);
+  inline explicit MaybeObjectHandle(Handle<Object> object);
+
+  static inline MaybeObjectHandle Weak(Object* object, Isolate* isolate);
+  static inline MaybeObjectHandle Weak(Handle<Object> object);
+
+  inline MaybeObject* operator*() const;
+  inline MaybeObject* operator->() const;
+  inline Handle<Object> object() const;
+
+  bool is_identical_to(const MaybeObjectHandle& other) const {
+    Handle<Object> this_handle;
+    Handle<Object> other_handle;
+    return reference_type_ == other.reference_type_ &&
+           handle_.ToHandle(&this_handle) ==
+               other.handle_.ToHandle(&other_handle) &&
+           this_handle.is_identical_to(other_handle);
+  }
+
+  bool is_null() const { return handle_.is_null(); }
+
+ private:
+  inline MaybeObjectHandle(Object* object,
+                           HeapObjectReferenceType reference_type,
+                           Isolate* isolate);
+  inline MaybeObjectHandle(Handle<Object> object,
+                           HeapObjectReferenceType reference_type);
+
+  HeapObjectReferenceType reference_type_;
+  MaybeHandle<Object> handle_;
+};
+
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_MAYBE_HANDLES_H_