// 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 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() = 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 = 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 MaybeHandle(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; } } // 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; }; // 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(Object object, Isolate* isolate); inline MaybeObjectHandle(MaybeObject object, LocalHeap* local_heap); inline MaybeObjectHandle(Object object, LocalHeap* local_heap); 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; inline bool is_identical_to(const MaybeObjectHandle& other) const; 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_HANDLES_MAYBE_HANDLES_H_