Add pdfium::MakeRetain<>() helper function.

core/fxcrt/cfx_retain_ptr.h

 // 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.
 
 #ifndef CORE_FXCRT_CFX_RETAIN_PTR_H_
 #define CORE_FXCRT_CFX_RETAIN_PTR_H_
 
 #include <memory>
+#include <utility>
 
 #include "core/fxcrt/fx_memory.h"
 
 template <class T>
 class CFX_RetainPtr {
  public:
   explicit CFX_RetainPtr(T* pObj) : m_pObj(pObj) {
     if (m_pObj)
       m_pObj->Retain();
   }
 
-  CFX_RetainPtr() : CFX_RetainPtr(nullptr) {}
+  CFX_RetainPtr() {}
   CFX_RetainPtr(const CFX_RetainPtr& that) : CFX_RetainPtr(that.Get()) {}
   CFX_RetainPtr(CFX_RetainPtr&& that) { Swap(that); }
 
   template <class U>
   CFX_RetainPtr(const CFX_RetainPtr<U>& that) : CFX_RetainPtr(that.Get()) {}
 
+  // Deliberately implicit to allow returning nullptrs.
+  CFX_RetainPtr(std::nullptr_t ptr) {}

[npm, 2016/11/29 22:25:30]

Can this go above, with the other constructors?

[Tom Sepez, 2016/11/29 22:36:23]

Done.  (Actually, the template at line 25 this is a ctor, too)

+
   void Reset(T* obj = nullptr) {
     if (obj)
       obj->Retain();
     m_pObj.reset(obj);
   }
 
   T* Get() const { return m_pObj.get(); }
   void Swap(CFX_RetainPtr& that) { m_pObj.swap(that.m_pObj); }
 
   CFX_RetainPtr& operator=(const CFX_RetainPtr& that) {
     if (*this != that)
       Reset(that.Get());
     return *this;
   }
 
   bool operator==(const CFX_RetainPtr& that) const {
     return Get() == that.Get();
   }
 
   bool operator!=(const CFX_RetainPtr& that) const { return !(*this == that); }
 
   explicit operator bool() const { return !!m_pObj; }
   T& operator*() const { return *m_pObj.get(); }
   T* operator->() const { return m_pObj.get(); }
 
  private:
   std::unique_ptr<T, ReleaseDeleter<T>> m_pObj;
 };
 
+// Trivial implementation - internal ref count with virtual destructor.
+class CFX_Retainable {
+ public:
+  void Retain() { ++m_nRefCount; }
+  void Release() {
+    if (--m_nRefCount == 0)
+      delete this;
+  }
+  bool HasOneRef() const { return m_nRefCount == 1; }
+
+ protected:
+  virtual ~CFX_Retainable() {}
+  intptr_t m_nRefCount = 0;
+};
+
+namespace pdfium {
+
+// Helper to make a CFX_RetainPtr along the lines of std::make_unique<>(),
+// or pdfium::MakeUnique<>(). Arguments are forwarded to T's constructor.
+template <typename T, typename... Args>
+CFX_RetainPtr<T> MakeRetain(Args&&... args) {
+  return CFX_RetainPtr<T>(new T(std::forward<Args>(args)...));
+}
+
+}  // namespace pdfium
+
 #endif  // CORE_FXCRT_CFX_RETAIN_PTR_H_