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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.
#ifndef V8_HANDLES_MAYBE_HANDLES_H_
#define V8_HANDLES_MAYBE_HANDLES_H_
#include <type_traits>
#include "src/handles/handles.h"
namespace v8 {
namespace internal {
struct NullMaybeHandleType {};
constexpr NullMaybeHandleType kNullMaybeHandle;
// ----------------------------------------------------------------------------
// 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 MaybeHandles 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() = default;
V8_INLINE MaybeHandle(NullMaybeHandleType) {}
// Constructor for handling automatic up casting from Handle.
// Ex. Handle<JSArray> can be passed when MaybeHandle<Object> is expected.
template <typename S, typename = std::enable_if_t<is_subtype_v<S, T>>>
V8_INLINE MaybeHandle(Handle<S> handle) : location_(handle.location_) {}
// Constructor for handling automatic up casting.
// Ex. MaybeHandle<JSArray> can be passed when MaybeHandle<Object> is
// expected.
template <typename S, typename = std::enable_if_t<is_subtype_v<S, T>>>
V8_INLINE MaybeHandle(MaybeHandle<S> maybe_handle)
: location_(maybe_handle.location_) {}
V8_INLINE MaybeHandle(Tagged<T> object, Isolate* isolate);
V8_INLINE MaybeHandle(Tagged<T> object, LocalHeap* local_heap);
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_WARN_UNUSED_RESULT V8_INLINE bool ToHandle(Handle<S>* out) const {
if (location_ == nullptr) {
*out = Handle<T>::null();
return false;
} else {
*out = Handle<T>(location_);
return true;
}
}
// Location equality.
bool equals(MaybeHandle<T> other) const {
return address() == other.address();
}
// 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; }
protected:
Address* location_ = nullptr;
// MaybeHandles of different classes are allowed to access each
// other's location_.
template <typename>
friend class MaybeHandle;
#ifdef V8_ENABLE_DIRECT_HANDLE
template <typename>
friend class MaybeDirectHandle;
#endif
};
template <typename T>
std::ostream& operator<<(std::ostream& os, MaybeHandle<T> handle);
// A handle which contains a potentially weak pointer. Keeps it alive (strongly)
// while the MaybeObjectHandle is alive.
class MaybeObjectHandle {
public:
inline MaybeObjectHandle()
: reference_type_(HeapObjectReferenceType::STRONG) {}
inline MaybeObjectHandle(MaybeObject object, Isolate* isolate);
inline MaybeObjectHandle(Tagged<Object> object, Isolate* isolate);
inline MaybeObjectHandle(MaybeObject object, LocalHeap* local_heap);
inline MaybeObjectHandle(Tagged<Object> object, LocalHeap* local_heap);
inline explicit MaybeObjectHandle(Handle<Object> object);
static inline MaybeObjectHandle Weak(Tagged<Object> object, Isolate* isolate);
static inline MaybeObjectHandle Weak(Handle<Object> object);
inline MaybeObject operator*() const;
inline MaybeObject operator->() const;
inline Handle<Object> object() const;
inline bool is_identical_to(const MaybeObjectHandle& other) const;
bool is_null() const { return handle_.is_null(); }
private:
inline MaybeObjectHandle(Tagged<Object> object,
HeapObjectReferenceType reference_type,
Isolate* isolate);
inline MaybeObjectHandle(Handle<Object> object,
HeapObjectReferenceType reference_type);
HeapObjectReferenceType reference_type_;
MaybeHandle<Object> handle_;
};
#ifdef V8_ENABLE_DIRECT_HANDLE
template <typename T>
class MaybeDirectHandle final {
public:
V8_INLINE MaybeDirectHandle() = default;
V8_INLINE MaybeDirectHandle(NullMaybeHandleType) {}
// Constructor for handling automatic up casting from DirectHandle.
// Ex. DirectHandle<JSArray> can be passed when MaybeDirectHandle<Object> is
// expected.
template <typename S, typename = std::enable_if_t<is_subtype_v<S, T>>>
V8_INLINE MaybeDirectHandle(DirectHandle<S> handle)
: location_(handle.address()) {}
// Constructor for handling automatic up casting from Handle.
// Ex. Handle<JSArray> can be passed when MaybeDirectHandle<Object> is
// expected.
template <typename S, typename = std::enable_if_t<is_subtype_v<S, T>>>
V8_INLINE MaybeDirectHandle(Handle<S> handle)
: MaybeDirectHandle(DirectHandle<S>(handle)) {}
// Constructor for handling automatic up casting.
// Ex. MaybeDirectHandle<JSArray> can be passed when MaybeDirectHandle<Object>
// is expected.
template <typename S, typename = std::enable_if_t<is_subtype_v<S, T>>>
V8_INLINE MaybeDirectHandle(MaybeDirectHandle<S> maybe_handle)
: location_(maybe_handle.location_) {}
// Constructor for handling automatic up casting from MaybeHandle.
// Ex. MaybeHandle<JSArray> can be passed when
// MaybeDirectHandle<Object> is expected.
template <typename S, typename = std::enable_if_t<is_subtype_v<S, T>>>
V8_INLINE MaybeDirectHandle(MaybeHandle<S> maybe_handle)
: location_(maybe_handle.location_ == nullptr ? kTaggedNullAddress
: *maybe_handle.location_) {
}
V8_INLINE MaybeDirectHandle(Tagged<T> object, Isolate* isolate);
V8_INLINE MaybeDirectHandle(Tagged<T> object, LocalHeap* local_heap);
V8_INLINE void Assert() const { DCHECK_NE(location_, kTaggedNullAddress); }
V8_INLINE void Check() const { CHECK_NE(location_, kTaggedNullAddress); }
V8_INLINE DirectHandle<T> ToHandleChecked() const {
Check();
return DirectHandle<T>(location_);
}
// Convert to a DirectHandle with a type that can be upcasted to.
template <typename S>
V8_WARN_UNUSED_RESULT V8_INLINE bool ToHandle(DirectHandle<S>* out) const {
if (location_ == kTaggedNullAddress) {
*out = DirectHandle<T>::null();
return false;
} else {
*out = DirectHandle<T>(location_);
return true;
}
}
// Returns the raw address where this direct handle is stored.
V8_INLINE Address address() const { return location_; }
bool is_null() const { return location_ == kTaggedNullAddress; }
protected:
Address location_ = kTaggedNullAddress;
// MaybeDirectHandles of different classes are allowed to access each
// other's location_.
template <typename>
friend class MaybeDirectHandle;
};
class MaybeObjectDirectHandle {
public:
inline MaybeObjectDirectHandle()
: reference_type_(HeapObjectReferenceType::STRONG) {}
inline MaybeObjectDirectHandle(MaybeObject object, Isolate* isolate);
inline MaybeObjectDirectHandle(Tagged<Object> object, Isolate* isolate);
inline MaybeObjectDirectHandle(MaybeObject object, LocalHeap* local_heap);
inline MaybeObjectDirectHandle(Tagged<Object> object, LocalHeap* local_heap);
inline explicit MaybeObjectDirectHandle(DirectHandle<Object> object);
static inline MaybeObjectDirectHandle Weak(Tagged<Object> object,
Isolate* isolate);
static inline MaybeObjectDirectHandle Weak(DirectHandle<Object> object);
inline MaybeObject operator*() const;
inline MaybeObject operator->() const;
inline DirectHandle<Object> object() const;
inline bool is_identical_to(const MaybeObjectDirectHandle& other) const;
bool is_null() const { return handle_.is_null(); }
private:
inline MaybeObjectDirectHandle(Tagged<Object> object,
HeapObjectReferenceType reference_type,
Isolate* isolate);
inline MaybeObjectDirectHandle(DirectHandle<Object> object,
HeapObjectReferenceType reference_type);
HeapObjectReferenceType reference_type_;
MaybeDirectHandle<Object> handle_;
};
#endif // V8_ENABLE_DIRECT_HANDLE
} // namespace internal
} // namespace v8
#endif // V8_HANDLES_MAYBE_HANDLES_H_
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