blob: 659ee3426b0593d7b4d146a1ba8f335df345cb1a [file] [log] [blame]
// Copyright 2014 The Chromium 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 "base/compiler_specific.h"
#include "base/logging.h"
#include "base/memory/scoped_policy.h"
namespace base {
// ScopedTypeRef<> is patterned after std::unique_ptr<>, but maintains ownership
// of a reference to any type that is maintained by Retain and Release methods.
// The Traits structure must provide the Retain and Release methods for type T.
// A default ScopedTypeRefTraits is used but not defined, and should be defined
// for each type to use this interface. For example, an appropriate definition
// of ScopedTypeRefTraits for CGLContextObj would be:
// template<>
// struct ScopedTypeRefTraits<CGLContextObj> {
// static CGLContextObj InvalidValue() { return nullptr; }
// static CGLContextObj Retain(CGLContextObj object) {
// CGLContextRetain(object);
// return object;
// }
// static void Release(CGLContextObj object) { CGLContextRelease(object); }
// };
// For the many types that have pass-by-pointer create functions, the function
// InitializeInto() is provided to allow direct initialization and assumption
// of ownership of the object. For example, continuing to use the above
// CGLContextObj specialization:
// base::ScopedTypeRef<CGLContextObj> context;
// CGLCreateContext(pixel_format, share_group, context.InitializeInto());
// For initialization with an existing object, the caller may specify whether
// the ScopedTypeRef<> being initialized is assuming the caller's existing
// ownership of the object (and should not call Retain in initialization) or if
// it should not assume this ownership and must create its own (by calling
// Retain in initialization). This behavior is based on the |policy| parameter,
// with |ASSUME| for the former and |RETAIN| for the latter. The default policy
// is to |ASSUME|.
template <typename T>
struct ScopedTypeRefTraits;
template <typename T, typename Traits = ScopedTypeRefTraits<T>>
class ScopedTypeRef {
typedef T element_type;
explicit constexpr ScopedTypeRef(
__unsafe_unretained T object = Traits::InvalidValue(),
base::scoped_policy::OwnershipPolicy policy = base::scoped_policy::ASSUME)
: object_(object) {
if (object_ && policy == base::scoped_policy::RETAIN)
object_ = Traits::Retain(object_);
ScopedTypeRef(const ScopedTypeRef<T, Traits>& that) : object_(that.object_) {
if (object_)
object_ = Traits::Retain(object_);
// This allows passing an object to a function that takes its superclass.
template <typename R, typename RTraits>
explicit ScopedTypeRef(const ScopedTypeRef<R, RTraits>& that_as_subclass)
: object_(that_as_subclass.get()) {
if (object_)
object_ = Traits::Retain(object_);
ScopedTypeRef(ScopedTypeRef<T, Traits>&& that) : object_(that.object_) {
that.object_ = Traits::InvalidValue();
~ScopedTypeRef() {
if (object_)
ScopedTypeRef& operator=(const ScopedTypeRef<T, Traits>& that) {
reset(that.get(), base::scoped_policy::RETAIN);
return *this;
// This is to be used only to take ownership of objects that are created
// by pass-by-pointer create functions. To enforce this, require that the
// object be reset to NULL before this may be used.
T* InitializeInto() WARN_UNUSED_RESULT {
return &object_;
void reset(__unsafe_unretained T object = Traits::InvalidValue(),
base::scoped_policy::OwnershipPolicy policy =
base::scoped_policy::ASSUME) {
if (object && policy == base::scoped_policy::RETAIN)
object = Traits::Retain(object);
if (object_)
object_ = object;
bool operator==(__unsafe_unretained T that) const { return object_ == that; }
bool operator!=(__unsafe_unretained T that) const { return object_ != that; }
operator T() const __attribute((ns_returns_not_retained)) { return object_; }
T get() const __attribute((ns_returns_not_retained)) { return object_; }
void swap(ScopedTypeRef& that) {
__unsafe_unretained T temp = that.object_;
that.object_ = object_;
object_ = temp;
// ScopedTypeRef<>::release() is like std::unique_ptr<>::release. It is NOT
// a wrapper for Release(). To force a ScopedTypeRef<> object to call
// Release(), use ScopedTypeRef<>::reset().
T release() __attribute((ns_returns_not_retained)) WARN_UNUSED_RESULT {
__unsafe_unretained T temp = object_;
object_ = Traits::InvalidValue();
return temp;
__unsafe_unretained T object_;
} // namespace base