// -*- 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:
* <code>refptr->memberfun()</code>.
*/
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