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livetrax/libs/glibmm2/glib/glibmm/refptr.h

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// -*- c++ -*-
#ifndef _GLIBMM_REFPTR_H
#define _GLIBMM_REFPTR_H
/* $Id: refptr.h 216 2005-04-07 08:28:46Z murrayc $ */
/* Copyright 2002 The gtkmm 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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/
namespace Glib
{
/** RefPtr<> is a reference-counting shared smartpointer.
*
* Some objects in gtkmm are obtained from a shared
* store. Consequently you cannot instantiate them yourself. Instead they
* return a RefPtr which behaves much like an ordinary pointer in that members
* can be reached with the usual <code>object_ptr->member</code> notation.
* Unlike most other smart pointers, RefPtr doesn't support dereferencing
* through <code>*object_ptr</code>.
*
* 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, meaning you don't need to remember
* to delete the object.
*
* RefPtr<> can store any class that has reference() and unreference() methods.
* In gtkmm, that is anything derived from Glib::ObjectBase, such as
* Gdk::Pixmap.
*
* See the "Memory Management" section in the "Programming with gtkmm"
* book for further information.
*/
template <class T_CppObject>
class RefPtr
{
public:
/** Default constructor
*
* Afterwards it will be null and use of -> will cause a segmentation fault.
*/
inline RefPtr();
/// Destructor - decrements reference count.
inline ~RefPtr();
/// For use only by the ::create() methods.
explicit inline RefPtr(T_CppObject* pCppObject);
/** Copy constructor
*
* This increments the shared reference count.
*/
inline RefPtr(const RefPtr<T_CppObject>& src);
/** Copy constructor (from different, but castable type).
*
* Increments the reference count.
*/
template <class T_CastFrom>
inline RefPtr(const RefPtr<T_CastFrom>& src);
/** 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);
/// Copy from another RefPtr:
inline RefPtr<T_CppObject>& operator=(const RefPtr<T_CppObject>& src);
/** Copy from different, but castable type).
*
* Increments the reference count.
*/
template <class T_CastFrom>
inline RefPtr<T_CppObject>& operator=(const RefPtr<T_CastFrom>& src);
/// Tests whether the RefPtr<> point to the same underlying instance.
inline bool operator==(const RefPtr<T_CppObject>& src) const;
/// See operator==().
inline bool operator!=(const RefPtr<T_CppObject>& src) const;
/** Dereferencing.
*
* Use the methods of the underlying instance like so:
* <code>refptr->memberfun()</code>.
*/
inline T_CppObject* operator->() const;
/** Test whether the RefPtr<> points to any underlying instance.
*
* Mimics usage of ordinary pointers:
* @code
* if (ptr)
* do_something();
* @endcode
*/
inline operator bool() const;
/// Set underlying instance to 0, decrementing reference count of existing instance appropriately.
inline void clear();
/** 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);
/** 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);
/** 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);
private:
T_CppObject* pCppObject_;
};
#ifndef DOXYGEN_SHOULD_SKIP_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
{
return pCppObject_;
}
template <class T_CppObject> inline
RefPtr<T_CppObject>::RefPtr()
:
pCppObject_ (0)
{}
template <class T_CppObject> inline
RefPtr<T_CppObject>::~RefPtr()
{
if(pCppObject_)
pCppObject_->unreference(); // This could cause pCppObject to be deleted.
}
template <class T_CppObject> inline
RefPtr<T_CppObject>::RefPtr(T_CppObject* pCppObject)
:
pCppObject_ (pCppObject)
{}
template <class T_CppObject> inline
RefPtr<T_CppObject>::RefPtr(const RefPtr<T_CppObject>& src)
:
pCppObject_ (src.pCppObject_)
{
if(pCppObject_)
pCppObject_->reference();
}
// 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)
:
// 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->())
{
if(pCppObject_)
pCppObject_->reference();
}
template <class T_CppObject> inline
void RefPtr<T_CppObject>::swap(RefPtr<T_CppObject>& other)
{
T_CppObject *const temp = pCppObject_;
pCppObject_ = other.pCppObject_;
other.pCppObject_ = temp;
}
template <class T_CppObject> inline
RefPtr<T_CppObject>& RefPtr<T_CppObject>::operator=(const RefPtr<T_CppObject>& src)
{
// 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>
template <class T_CastFrom>
inline
RefPtr<T_CppObject>& RefPtr<T_CppObject>::operator=(const RefPtr<T_CastFrom>& src)
{
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
{
return (pCppObject_ == src.pCppObject_);
}
template <class T_CppObject> inline
bool RefPtr<T_CppObject>::operator!=(const RefPtr<T_CppObject>& src) const
{
return (pCppObject_ != src.pCppObject_);
}
template <class T_CppObject> inline
RefPtr<T_CppObject>::operator bool() const
{
return (pCppObject_ != 0);
}
template <class T_CppObject> inline
void RefPtr<T_CppObject>::clear()
{
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)
{
T_CppObject *const pCppObject = dynamic_cast<T_CppObject*>(src.operator->());
if(pCppObject)
pCppObject->reference();
return RefPtr<T_CppObject>(pCppObject);
}
template <class T_CppObject>
template <class T_CastFrom>
inline
RefPtr<T_CppObject> RefPtr<T_CppObject>::cast_static(const RefPtr<T_CastFrom>& src)
{
T_CppObject *const pCppObject = static_cast<T_CppObject*>(src.operator->());
if(pCppObject)
pCppObject->reference();
return RefPtr<T_CppObject>(pCppObject);
}
template <class T_CppObject>
template <class T_CastFrom>
inline
RefPtr<T_CppObject> RefPtr<T_CppObject>::cast_const(const RefPtr<T_CastFrom>& src)
{
T_CppObject *const pCppObject = const_cast<T_CppObject*>(src.operator->());
if(pCppObject)
pCppObject->reference();
return RefPtr<T_CppObject>(pCppObject);
}
#endif /* DOXYGEN_SHOULD_SKIP_THIS */
/** @relates Glib::RefPtr */
template <class T_CppObject> inline
void swap(RefPtr<T_CppObject>& lhs, RefPtr<T_CppObject>& rhs)
{
lhs.swap(rhs);
}
} // namespace Glib
#endif /* _GLIBMM_REFPTR_H */