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// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Provides a smart pointer class for intrusively reference-counted objects.
#ifndef FLUTTER_FML_MEMORY_REF_PTR_H_
#define FLUTTER_FML_MEMORY_REF_PTR_H_
#include <cstddef>
#include <functional>
#include <utility>
#include "flutter/fml/logging.h"
#include "flutter/fml/macros.h"
#include "flutter/fml/memory/ref_ptr_internal.h"
namespace fml {
// A smart pointer class for intrusively reference-counted objects (e.g., those
// subclassing |RefCountedThreadSafe| -- see ref_counted.h).
//
// Such objects require *adoption* to obtain the first |RefPtr|, which is
// accomplished using |AdoptRef| (see below). (This is due to such objects being
// constructed with a reference count of 1. The adoption requirement is
// enforced, at least in Debug builds, by assertions.)
//
// E.g., if |Foo| is an intrusively reference-counted class:
//
// // The |AdoptRef| may be put in a static factory method (e.g., if |Foo|'s
// // constructor is private).
// RefPtr<Foo> my_foo_ptr(AdoptRef(new Foo()));
//
// // Now OK, since "my Foo" has been adopted ...
// RefPtr<Foo> another_ptr_to_my_foo(my_foo_ptr.get());
//
// // ... though this would preferable in this situation.
// RefPtr<Foo> yet_another_ptr_to_my_foo(my_foo_ptr);
//
// Unlike Chromium's |scoped_refptr|, |RefPtr| is only explicitly constructible
// from a plain pointer (and not assignable). It is however implicitly
// constructible from |nullptr|. So:
//
// RefPtr<Foo> foo(plain_ptr_to_adopted_foo); // OK.
// foo = plain_ptr_to_adopted_foo; // Not OK (doesn't compile).
// foo = RefPtr<Foo>(plain_ptr_to_adopted_foo); // OK.
// foo = nullptr; // OK.
//
// And if we have |void MyFunction(RefPtr<Foo> foo)|, calling it using
// |MyFunction(nullptr)| is also valid.
//
// Implementation note: For copy/move constructors/operator=s, we often have
// templated versions, so that the operation can be done on a |RefPtr<U>|, where
// |U| is a subclass of |T|. However, we also have non-templated versions with
// |U = T|, since the templated versions don't count as copy/move
// constructors/operator=s for the purposes of causing the default copy
// constructor/operator= to be deleted. E.g., if we didn't declare any
// non-templated versions, we'd get the default copy constructor/operator= (we'd
// only not get the default move constructor/operator= by virtue of having a
// destructor)! (In fact, it'd suffice to only declare a non-templated move
// constructor or move operator=, which would cause the copy
// constructor/operator= to be deleted, but for clarity we include explicit
// non-templated versions of everything.)
template <typename T>
class RefPtr final {
public:
RefPtr() : ptr_(nullptr) {}
RefPtr(std::nullptr_t) // NOLINT(google-explicit-constructor)
: ptr_(nullptr) {}
// Explicit constructor from a plain pointer (to an object that must have
// already been adopted). (Note that in |T::T()|, references to |this| cannot
// be taken, since the object being constructed will not have been adopted
// yet.)
template <typename U>
explicit RefPtr(U* p) : ptr_(p) {
if (ptr_) {
ptr_->AddRef();
}
}
// Copy constructor.
RefPtr(const RefPtr<T>& r) // NOLINT(google-explicit-constructor)
: ptr_(r.ptr_) {
if (ptr_) {
ptr_->AddRef();
}
}
template <typename U>
RefPtr(const RefPtr<U>& r) // NOLINT(google-explicit-constructor)
: ptr_(r.ptr_) {
if (ptr_) {
ptr_->AddRef();
}
}
// Move constructor.
RefPtr(RefPtr<T>&& r) : ptr_(r.ptr_) { // NOLINT(google-explicit-constructor)
r.ptr_ = nullptr;
}
template <typename U>
RefPtr(RefPtr<U>&& r) : ptr_(r.ptr_) { // NOLINT(google-explicit-constructor)
r.ptr_ = nullptr;
}
// Destructor.
~RefPtr() {
if (ptr_) {
ptr_->Release();
}
}
T* get() const { return ptr_; }
T& operator*() const {
FML_DCHECK(ptr_);
return *ptr_;
}
T* operator->() const {
FML_DCHECK(ptr_);
return ptr_;
}
// Copy assignment.
RefPtr<T>& operator=(const RefPtr<T>& r) {
// Handle self-assignment.
if (r.ptr_ == ptr_) {
return *this;
}
if (r.ptr_) {
r.ptr_->AddRef();
}
T* old_ptr = ptr_;
ptr_ = r.ptr_;
if (old_ptr) {
old_ptr->Release();
}
return *this;
}
template <typename U>
RefPtr<T>& operator=(const RefPtr<U>& r) {
if (reinterpret_cast<T*>(r.ptr_) == ptr_) {
return *this;
}
if (r.ptr_) {
r.ptr_->AddRef();
}
T* old_ptr = ptr_;
ptr_ = r.ptr_;
if (old_ptr) {
old_ptr->Release();
}
return *this;
}
// Move assignment.
// Note: Like |std::shared_ptr|, we support self-move and move assignment is
// equivalent to |RefPtr<T>(std::move(r)).swap(*this)|.
RefPtr<T>& operator=(RefPtr<T>&& r) {
RefPtr<T>(std::move(r)).swap(*this);
return *this;
}
template <typename U>
RefPtr<T>& operator=(RefPtr<U>&& r) {
RefPtr<T>(std::move(r)).swap(*this);
return *this;
}
void swap(RefPtr<T>& r) {
T* p = ptr_;
ptr_ = r.ptr_;
r.ptr_ = p;
}
// Returns a new |RefPtr<T>| with the same contents as this pointer. Useful
// when a function takes a |RefPtr<T>&&| argument and the caller wants to
// retain its reference (rather than moving it).
RefPtr<T> Clone() const { return *this; }
explicit operator bool() const { return !!ptr_; }
template <typename U>
bool operator==(const RefPtr<U>& rhs) const {
return ptr_ == rhs.ptr_;
}
template <typename U>
bool operator!=(const RefPtr<U>& rhs) const {
return !operator==(rhs);
}
template <typename U>
bool operator<(const RefPtr<U>& rhs) const {
return ptr_ < rhs.ptr_;
}
private:
template <typename U>
friend class RefPtr;
friend RefPtr<T> AdoptRef<T>(T*);
enum AdoptTag { kAdopt };
RefPtr(T* ptr, AdoptTag) : ptr_(ptr) { FML_DCHECK(ptr_); }
T* ptr_;
};
// Adopts a newly-created |T|. Typically used in a static factory method, like:
//
// // static
// RefPtr<Foo> Foo::Create() {
// return AdoptRef(new Foo());
// }
template <typename T>
inline RefPtr<T> AdoptRef(T* ptr) {
#ifndef NDEBUG
ptr->Adopt();
#endif
return RefPtr<T>(ptr, RefPtr<T>::kAdopt);
}
// Constructs a |RefPtr<T>| from a plain pointer (to an object that must
// have already been adoped). Avoids having to spell out the full type name.
//
// Foo* foo = ...;
// auto foo_ref = Ref(foo);
//
// (|foo_ref| will be of type |RefPtr<Foo>|.)
template <typename T>
inline RefPtr<T> Ref(T* ptr) {
return RefPtr<T>(ptr);
}
// Creates an intrusively reference counted |T|, producing a |RefPtr<T>| (and
// performing the required adoption). Use like:
//
// auto my_foo = MakeRefCounted<Foo>(ctor_arg1, ctor_arg2);
//
// (|my_foo| will be of type |RefPtr<Foo>|.)
template <typename T, typename... Args>
RefPtr<T> MakeRefCounted(Args&&... args) {
return internal::MakeRefCountedHelper<T>::MakeRefCounted(
std::forward<Args>(args)...);
}
} // namespace fml
// Inject custom std::hash<> function object for |RefPtr<T>|.
namespace std {
template <typename T>
struct hash<fml::RefPtr<T>> {
using argument_type = fml::RefPtr<T>;
using result_type = std::size_t;
result_type operator()(const argument_type& ptr) const {
return std::hash<T*>()(ptr.get());
}
};
} // namespace std
#endif // FLUTTER_FML_MEMORY_REF_PTR_H_