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// Copyright 2016 PDFium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
// Original code copyright 2014 Foxit Software Inc.
#include "core/fxcrt/fx_system.h"
#include "core/fxcrt/retain_ptr.h"
namespace fxcrt {
// A shared pointer to an object with Copy on Write semantics that makes it
// appear as if all instances were independent. |ObjClass| must implement the
// requirements of |Retainable| from retain_ptr.h, and must also provide a
// Clone() method. Often this will just call MakeRetain<>(*this) but will need
// to be virtual if |ObjClass| is subclassed.
template <class ObjClass>
class SharedCopyOnWrite {
SharedCopyOnWrite() {}
SharedCopyOnWrite(const SharedCopyOnWrite& other)
: m_pObject(other.m_pObject) {}
~SharedCopyOnWrite() {}
template <typename... Args>
ObjClass* Emplace(Args... params) {
m_pObject = pdfium::MakeRetain<ObjClass>(params...);
return m_pObject.Get();
SharedCopyOnWrite& operator=(const SharedCopyOnWrite& that) {
if (*this != that)
m_pObject = that.m_pObject;
return *this;
void SetNull() { m_pObject.Reset(); }
const ObjClass* GetObject() const { return m_pObject.Get(); }
template <typename... Args>
ObjClass* GetPrivateCopy(Args... params) {
if (!m_pObject)
return Emplace(params...);
if (!m_pObject->HasOneRef())
m_pObject = m_pObject->Clone();
return m_pObject.Get();
bool operator==(const SharedCopyOnWrite& that) const {
return m_pObject == that.m_pObject;
bool operator!=(const SharedCopyOnWrite& that) const {
return !(*this == that);
explicit operator bool() const { return !!m_pObject; }
RetainPtr<ObjClass> m_pObject;
} // namespace fxcrt
using fxcrt::SharedCopyOnWrite;