// -*- c++ -*-

#ifndef _cairo_REFPTR_H

#define _cairo_REFPTR_H

/* $Id: refptr.h,v 1.6 2006-09-27 18:38:57 murrayc Exp $ */

/* Copyright 2005 The cairomm Development Team

 *

 * This library is free software; you can redistribute it and/or

 * modify it under the terms of the GNU Library General Public

 * License as published by the Free Software Foundation; either

 * version 2 of the License, or (at your option) any later version.

 *

 * This library is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU

 * Library General Public License for more details.

 *

 * You should have received a copy of the GNU Library General Public

 * License along with this library; if not, write to the Free Software

 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA

 * 02110-1301, USA.

 */

#include <utility>

namespace Cairo

{

//TODO: Use std::shared_ptr<> instead when we can break ABI.

/** RefPtr<> is a reference-counting shared smartpointer.

 *

 * Reference counting means that a shared reference count is incremented each

 * time a RefPtr is copied, and decremented each time a RefPtr is destroyed,

 * for instance when it leaves its scope. When the reference count reaches

 * zero, the contained object is deleted

 *

 * cairomm uses RefPtr so that you don't need to remember

 * to delete the object explicitly, or know when a method expects you to delete 

 * the object that it returns, and to prevent any need to manually  reference 

 * and unreference() cairo objects.

 */

template <class T_CppObject>

class RefPtr

{

public:

  // Let the cast constructors and assignement operators access private data.

  template <typename T_CastFrom>

  friend class RefPtr;

  /** Default constructor

   *

   * Afterwards it will be null and use of -> will cause a segmentation fault.

   */

  inline RefPtr() noexcept;

  /// Destructor - decrements reference count.

  inline ~RefPtr() noexcept;

  /** For use only in the internal implementation of cairomm, gtkmm, etc.

   *

   * This takes ownership of @a pCppObject, so it will be deleted when the 

   * last RefPtr is deleted, for instance when it goes out of scope.

   *

   * This assumes that @a pCppObject already has a starting reference for its underlying cairo object,

   * so that destruction of @a @pCppObject will cause a corresponding unreference of its underlying 

   * cairo object. For instance, a cairo_*_create() function usually provides a starting reference, 

   * but a cairo_*_get_*() function requires the caller to manually reference the returned object.

   * In this case, you should call reference() on @a pCppObject before passing it to this constructor.

   */

  explicit inline RefPtr(T_CppObject* pCppObject) noexcept;

  ///  For use only in the internal implementation of sharedptr.

  explicit inline RefPtr(T_CppObject* pCppObject, int* refcount) noexcept;

  /** Move constructor

   */

  inline RefPtr(RefPtr&& src) noexcept;

  /** Move constructor (from different, but castable type).

   */

  template <class T_CastFrom>

  inline RefPtr(RefPtr<T_CastFrom>&& src) noexcept;

  /** Copy constructor

   *

   * This increments the shared reference count.

   */

  inline RefPtr(const RefPtr<T_CppObject>& src) noexcept;

  /** Copy constructor (from different, but castable type).

   *

   * Increments the reference count.

   */

  template <class T_CastFrom>

  inline RefPtr(const RefPtr<T_CastFrom>& src) noexcept;

  /** Swap the contents of two RefPtr<>.

   * This method swaps the internal pointers to T_CppObject.  This can be

   * done safely without involving a reference/unreference cycle and is

   * therefore highly efficient.

   */

  inline void swap(RefPtr<T_CppObject>& other) noexcept;

  /// Copy from another RefPtr:

  inline RefPtr<T_CppObject>& operator=(const RefPtr<T_CppObject>& src) noexcept;

  /** Copy from different, but castable type).

   *

   * Increments the reference count.

   */

  template <class T_CastFrom>

  inline RefPtr<T_CppObject>& operator=(const RefPtr<T_CastFrom>& src) noexcept;

  /// Move assignment operator:

  inline RefPtr& operator=(RefPtr&& src) noexcept;

  /// Move assignment operator (from different, but castable type):

  template <class T_CastFrom>

  inline RefPtr& operator=(RefPtr<T_CastFrom>&& src) noexcept;

  /// Tests whether the RefPtr<> point to the same underlying instance.

  inline bool operator==(const RefPtr<T_CppObject>& src) const noexcept;

  /// See operator==().

  inline bool operator!=(const RefPtr<T_CppObject>& src) const noexcept;

  /** Dereferencing.

   *

   * Use the methods of the underlying instance like so:

   * refptr->memberfun().

   */

  inline T_CppObject* operator->() const noexcept;

  /** Test whether the RefPtr<> points to any underlying instance.

   *

   * Mimics usage of ordinary pointers:

   * @code

   *   if (ptr)

   *     do_something();

   * @endcode

   */

  inline operator bool() const noexcept;

  /// Set underlying instance to 0, decrementing reference count of existing instance appropriately.

  inline void clear() noexcept;

  /** Dynamic cast to derived class.

   *

   * The RefPtr can't be cast with the usual notation so instead you can use

   * @code

   *   ptr_derived = RefPtr<Derived>::cast_dynamic(ptr_base);

   * @endcode

   */

  template <class T_CastFrom>

  static inline RefPtr<T_CppObject> cast_dynamic(const RefPtr<T_CastFrom>& src) noexcept;

  /** Static cast to derived class.

   *

   * Like the dynamic cast; the notation is 

   * @code

   *   ptr_derived = RefPtr<Derived>::cast_static(ptr_base);

   * @endcode

   */

  template <class T_CastFrom>

  static inline RefPtr<T_CppObject> cast_static(const RefPtr<T_CastFrom>& src) noexcept;

  /** Cast to non-const.

   *

   * The RefPtr can't be cast with the usual notation so instead you can use

   * @code

   *   ptr_unconst = RefPtr<UnConstType>::cast_const(ptr_const);

   * @endcode

   */

  template <class T_CastFrom>

  static inline RefPtr<T_CppObject> cast_const(const RefPtr<T_CastFrom>& src) noexcept;

#ifndef DOXYGEN_IGNORE_THIS

  // Warning: This is for internal use only.  Do not manually modify the

  // reference count with this pointer.

  inline int* refcount_() const noexcept { return pCppRefcount_; }

#endif // DOXYGEN_IGNORE_THIS

private:

  void unref() noexcept;

  T_CppObject* pCppObject_;

  mutable int* pCppRefcount_;

};

#ifndef DOXYGEN_IGNORE_THIS

// RefPtr<>::operator->() comes first here since it's used by other methods.

// If it would come after them it wouldn't be inlined.

template <class T_CppObject> inline

T_CppObject* RefPtr<T_CppObject>::operator->() const noexcept

{

  return pCppObject_;

}

template <class T_CppObject> inline

RefPtr<T_CppObject>::RefPtr() noexcept

:

  pCppObject_(nullptr),

  pCppRefcount_(0)

{}

template <class T_CppObject> inline

RefPtr<T_CppObject>::~RefPtr() noexcept

{

  unref();

}

template <class T_CppObject> inline

void RefPtr<T_CppObject>::unref() noexcept

{

  if(pCppRefcount_)

  {

    --(*pCppRefcount_);

    if(*pCppRefcount_ == 0)

    {

      if(pCppObject_)

      {

        delete pCppObject_;

        pCppObject_ = nullptr;

      }

      delete pCppRefcount_;

      pCppRefcount_ = nullptr;

    }

  }

}

template <class T_CppObject> inline

RefPtr<T_CppObject>::RefPtr(T_CppObject* pCppObject) noexcept

:

  pCppObject_(pCppObject),

  pCppRefcount_(0)

{

  if(pCppObject)

  {

    pCppRefcount_ = new int;

    *pCppRefcount_ = 1; //This will be decremented in the destructor.

  }

}

//Used by cast_*() implementations:

template <class T_CppObject> inline

RefPtr<T_CppObject>::RefPtr(T_CppObject* pCppObject, int* refcount) noexcept

:

  pCppObject_(pCppObject),

  pCppRefcount_(refcount)

{

  if(pCppObject_ && pCppRefcount_)

    ++(*pCppRefcount_);

}

template <class T_CppObject> inline

RefPtr<T_CppObject>::RefPtr(const RefPtr<T_CppObject>& src) noexcept

:

  pCppObject_ (src.pCppObject_),

  pCppRefcount_(src.pCppRefcount_)

{

  if(pCppObject_ && pCppRefcount_)

    ++(*pCppRefcount_);

}

template <class T_CppObject> inline

RefPtr<T_CppObject>::RefPtr(RefPtr&& src) noexcept

:

  pCppObject_ (src.pCppObject_),

  pCppRefcount_ (src.pCppRefcount_)

{

  src.pCppObject_ = nullptr;

  src.pCppRefcount_ = nullptr;

}

template <class T_CppObject>

  template <class T_CastFrom>

inline

RefPtr<T_CppObject>::RefPtr(RefPtr<T_CastFrom>&& src) noexcept

:

  pCppObject_ (src.pCppObject_),

  pCppRefcount_ (src.pCppRefcount_)

{

  src.pCppObject_ = nullptr;

  src.pCppRefcount_ = nullptr;

}

// The templated ctor allows copy construction from any object that's

// castable.  Thus, it does downcasts:

//   base_ref = derived_ref

template <class T_CppObject>

  template <class T_CastFrom>

inline

RefPtr<T_CppObject>::RefPtr(const RefPtr<T_CastFrom>& src) noexcept

:

  // Without the friend delaration,

  // a different RefPtr<> will not allow us access to pCppObject_.  We need

  // to add a get_underlying() for this, but that would encourage incorrect

  // use, so we use the less well-known operator->() accessor:

  pCppObject_ (src.operator->()),

  pCppRefcount_(src.refcount_())

{

  if(pCppObject_ && pCppRefcount_)

    ++(*pCppRefcount_);

}

template <class T_CppObject> inline

void RefPtr<T_CppObject>::swap(RefPtr<T_CppObject>& other) noexcept

{

  T_CppObject *const temp = pCppObject_;

  int* temp_count = pCppRefcount_; 

  pCppObject_ = other.pCppObject_;

  pCppRefcount_ = other.pCppRefcount_;

  other.pCppObject_ = temp;

  other.pCppRefcount_ = temp_count;

}

template <class T_CppObject> inline

RefPtr<T_CppObject>& RefPtr<T_CppObject>::operator=(const RefPtr<T_CppObject>& src) noexcept

{

  // In case you haven't seen the swap() technique to implement copy

  // assignment before, here's what it does:

  //

  // 1) Create a temporary RefPtr<> instance via the copy ctor, thereby

  //    increasing the reference count of the source object.

  //

  // 2) Swap the internal object pointers of *this and the temporary

  //    RefPtr<>.  After this step, *this already contains the new pointer,

  //    and the old pointer is now managed by temp.

  //

  // 3) The destructor of temp is executed, thereby unreferencing the

  //    old object pointer.

  //

  // This technique is described in Herb Sutter's "Exceptional C++", and

  // has a number of advantages over conventional approaches:

  //

  // - Code reuse by calling the copy ctor.

  // - Strong exception safety for free.

  // - Self assignment is handled implicitely.

  // - Simplicity.

  // - It just works and is hard to get wrong; i.e. you can use it without

  //   even thinking about it to implement copy assignment whereever the

  //   object data is managed indirectly via a pointer, which is very common.

  RefPtr<T_CppObject> temp (src);

  this->swap(temp);

  return *this;

}

template <class T_CppObject> inline

RefPtr<T_CppObject>& RefPtr<T_CppObject>::operator=(RefPtr&& src) noexcept

{

  RefPtr<T_CppObject> temp (std::move(src));

  this->swap(temp);

  src.pCppObject_ = nullptr;

  src.pCppRefcount_ = nullptr;

  return *this;

}

template <class T_CppObject>

  template <class T_CastFrom>

inline

RefPtr<T_CppObject>& RefPtr<T_CppObject>::operator=(RefPtr<T_CastFrom>&& src) noexcept

{

  RefPtr<T_CppObject> temp (std::move(src));

  this->swap(temp);

  src.pCppObject_ = nullptr;

  src.pCppRefcount_ = nullptr;

  return *this;

}

template <class T_CppObject>

  template <class T_CastFrom>

inline

RefPtr<T_CppObject>& RefPtr<T_CppObject>::operator=(const RefPtr<T_CastFrom>& src) noexcept

{

  RefPtr<T_CppObject> temp (src);

  this->swap(temp);

  return *this;

}

template <class T_CppObject> inline

bool RefPtr<T_CppObject>::operator==(const RefPtr<T_CppObject>& src) const noexcept

{

  return (pCppObject_ == src.pCppObject_);

}

template <class T_CppObject> inline

bool RefPtr<T_CppObject>::operator!=(const RefPtr<T_CppObject>& src) const noexcept

{

  return (pCppObject_ != src.pCppObject_);

}

template <class T_CppObject> inline

RefPtr<T_CppObject>::operator bool() const noexcept

{

  return (pCppObject_ != 0);

}

template <class T_CppObject> inline

void RefPtr<T_CppObject>::clear() noexcept

{

  RefPtr<T_CppObject> temp; // swap with an empty RefPtr<> to clear *this

  this->swap(temp);

}

template <class T_CppObject>

  template <class T_CastFrom>

inline

RefPtr<T_CppObject> RefPtr<T_CppObject>::cast_dynamic(const RefPtr<T_CastFrom>& src) noexcept

{

  T_CppObject *const pCppObject = dynamic_cast<T_CppObject*>(src.operator->());

  if(pCppObject) //Check whether dynamic_cast<> succeeded so we don't pass a null object with a used refcount:

    return RefPtr<T_CppObject>(pCppObject, src.refcount_());

  else

    return RefPtr<T_CppObject>();

}

template <class T_CppObject>

  template <class T_CastFrom>

inline

RefPtr<T_CppObject> RefPtr<T_CppObject>::cast_static(const RefPtr<T_CastFrom>& src) noexcept

{

  T_CppObject *const pCppObject = static_cast<T_CppObject*>(src.operator->());

  return RefPtr<T_CppObject>(pCppObject, src.refcount_());

}

template <class T_CppObject>

  template <class T_CastFrom>

inline

RefPtr<T_CppObject> RefPtr<T_CppObject>::cast_const(const RefPtr<T_CastFrom>& src) noexcept

{

  T_CppObject *const pCppObject = const_cast<T_CppObject*>(src.operator->());

  return RefPtr<T_CppObject>(pCppObject, src.refcount_());

}

#endif /* DOXYGEN_IGNORE_THIS */

/** @relates Glib::RefPtr */

template <class T_CppObject> inline

void swap(RefPtr<T_CppObject>& lhs, RefPtr<T_CppObject>& rhs) noexcept

{

  lhs.swap(rhs);

}

} // namespace Cairo

#endif /* _cairo_REFPTR_H */

// vim: ts=2 sw=2 et