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// 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.
#include <type_traits>
#include "src/handles/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 {
V8_INLINE MaybeHandle() = default;
// 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_(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_(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 {
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 reinterpret_cast<Address>(location_);
bool is_null() const { return location_ == nullptr; }
Address* 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 {
inline MaybeObjectHandle()
: reference_type_(HeapObjectReferenceType::STRONG) {}
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) &&
bool is_null() const { return handle_.is_null(); }
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