342 lines
9.6 KiB
C++
342 lines
9.6 KiB
C++
// -*- c++ -*-
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#ifndef _GLIBMM_REFPTR_H
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#define _GLIBMM_REFPTR_H
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/* $Id: refptr.h,v 1.4 2005/04/07 08:28:46 murrayc Exp $ */
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/* Copyright 2002 The gtkmm Development Team
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*
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* This library is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Library General Public
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* License as published by the Free Software Foundation; either
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* version 2 of the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Library General Public License for more details.
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*
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* You should have received a copy of the GNU Library General Public
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* License along with this library; if not, write to the Free
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* Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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namespace Glib
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{
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/** RefPtr<> is a reference-counting shared smartpointer.
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*
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* Some objects in gtkmm are obtained from a shared
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* store. Consequently you cannot instantiate them yourself. Instead they
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* return a RefPtr which behaves much like an ordinary pointer in that members
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* can be reached with the usual <code>object_ptr->member</code> notation.
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* Unlike most other smart pointers, RefPtr doesn't support dereferencing
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* through <code>*object_ptr</code>.
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*
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* Reference counting means that a shared reference count is incremented each
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* time a RefPtr is copied, and decremented each time a RefPtr is destroyed,
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* for instance when it leaves its scope. When the reference count reaches
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* zero, the contained object is deleted, meaning you don't need to remember
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* to delete the object.
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*
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* RefPtr<> can store any class that has reference() and unreference() methods.
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* In gtkmm, that is anything derived from Glib::ObjectBase, such as
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* Gdk::Pixmap.
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*
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* See the "Memory Management" section in the "Programming with gtkmm"
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* book for further information.
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*/
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template <class T_CppObject>
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class RefPtr
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{
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public:
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/** Default constructor
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*
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* Afterwards it will be null and use of -> will cause a segmentation fault.
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*/
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inline RefPtr();
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/// Destructor - decrements reference count.
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inline ~RefPtr();
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/// For use only by the ::create() methods.
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explicit inline RefPtr(T_CppObject* pCppObject);
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/** Copy constructor
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*
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* This increments the shared reference count.
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*/
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inline RefPtr(const RefPtr<T_CppObject>& src);
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/** Copy constructor (from different, but castable type).
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*
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* Increments the reference count.
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*/
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template <class T_CastFrom>
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inline RefPtr(const RefPtr<T_CastFrom>& src);
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/** Swap the contents of two RefPtr<>.
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* This method swaps the internal pointers to T_CppObject. This can be
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* done safely without involving a reference/unreference cycle and is
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* therefore highly efficient.
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*/
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inline void swap(RefPtr<T_CppObject>& other);
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/// Copy from another RefPtr:
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inline RefPtr<T_CppObject>& operator=(const RefPtr<T_CppObject>& src);
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/** Copy from different, but castable type).
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*
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* Increments the reference count.
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*/
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template <class T_CastFrom>
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inline RefPtr<T_CppObject>& operator=(const RefPtr<T_CastFrom>& src);
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/// Tests whether the RefPtr<> point to the same underlying instance.
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inline bool operator==(const RefPtr<T_CppObject>& src) const;
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/// See operator==().
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inline bool operator!=(const RefPtr<T_CppObject>& src) const;
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/** Dereferencing.
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*
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* Use the methods of the underlying instance like so:
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* <code>refptr->memberfun()</code>.
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*/
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inline T_CppObject* operator->() const;
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/** Test whether the RefPtr<> points to any underlying instance.
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*
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* Mimics usage of ordinary pointers:
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* @code
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* if (ptr)
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* do_something();
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* @endcode
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*/
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inline operator bool() const;
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/// Set underlying instance to 0, decrementing reference count of existing instance appropriately.
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inline void clear();
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/** Dynamic cast to derived class.
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*
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* The RefPtr can't be cast with the usual notation so instead you can use
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* @code
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* ptr_derived = RefPtr<Derived>::cast_dynamic(ptr_base);
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* @endcode
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*/
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template <class T_CastFrom>
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static inline RefPtr<T_CppObject> cast_dynamic(const RefPtr<T_CastFrom>& src);
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/** Static cast to derived class.
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*
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* Like the dynamic cast; the notation is
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* @code
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* ptr_derived = RefPtr<Derived>::cast_static(ptr_base);
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* @endcode
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*/
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template <class T_CastFrom>
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static inline RefPtr<T_CppObject> cast_static(const RefPtr<T_CastFrom>& src);
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/** Cast to non-const.
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*
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* The RefPtr can't be cast with the usual notation so instead you can use
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* @code
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* ptr_unconst = RefPtr<UnConstType>::cast_const(ptr_const);
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* @endcode
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*/
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template <class T_CastFrom>
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static inline RefPtr<T_CppObject> cast_const(const RefPtr<T_CastFrom>& src);
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private:
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T_CppObject* pCppObject_;
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};
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#ifndef DOXYGEN_SHOULD_SKIP_THIS
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// RefPtr<>::operator->() comes first here since it's used by other methods.
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// If it would come after them it wouldn't be inlined.
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template <class T_CppObject> inline
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T_CppObject* RefPtr<T_CppObject>::operator->() const
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{
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return pCppObject_;
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}
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template <class T_CppObject> inline
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RefPtr<T_CppObject>::RefPtr()
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:
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pCppObject_ (0)
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{}
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template <class T_CppObject> inline
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RefPtr<T_CppObject>::~RefPtr()
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{
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if(pCppObject_)
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pCppObject_->unreference(); // This could cause pCppObject to be deleted.
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}
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template <class T_CppObject> inline
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RefPtr<T_CppObject>::RefPtr(T_CppObject* pCppObject)
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:
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pCppObject_ (pCppObject)
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{}
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template <class T_CppObject> inline
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RefPtr<T_CppObject>::RefPtr(const RefPtr<T_CppObject>& src)
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:
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pCppObject_ (src.pCppObject_)
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{
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if(pCppObject_)
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pCppObject_->reference();
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}
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// The templated ctor allows copy construction from any object that's
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// castable. Thus, it does downcasts:
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// base_ref = derived_ref
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template <class T_CppObject>
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template <class T_CastFrom>
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inline
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RefPtr<T_CppObject>::RefPtr(const RefPtr<T_CastFrom>& src)
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:
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// A different RefPtr<> will not allow us access to pCppObject_. We need
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// to add a get_underlying() for this, but that would encourage incorrect
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// use, so we use the less well-known operator->() accessor:
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pCppObject_ (src.operator->())
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{
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if(pCppObject_)
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pCppObject_->reference();
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}
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template <class T_CppObject> inline
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void RefPtr<T_CppObject>::swap(RefPtr<T_CppObject>& other)
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{
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T_CppObject *const temp = pCppObject_;
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pCppObject_ = other.pCppObject_;
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other.pCppObject_ = temp;
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}
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template <class T_CppObject> inline
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RefPtr<T_CppObject>& RefPtr<T_CppObject>::operator=(const RefPtr<T_CppObject>& src)
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{
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// In case you haven't seen the swap() technique to implement copy
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// assignment before, here's what it does:
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//
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// 1) Create a temporary RefPtr<> instance via the copy ctor, thereby
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// increasing the reference count of the source object.
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//
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// 2) Swap the internal object pointers of *this and the temporary
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// RefPtr<>. After this step, *this already contains the new pointer,
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// and the old pointer is now managed by temp.
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//
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// 3) The destructor of temp is executed, thereby unreferencing the
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// old object pointer.
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//
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// This technique is described in Herb Sutter's "Exceptional C++", and
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// has a number of advantages over conventional approaches:
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//
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// - Code reuse by calling the copy ctor.
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// - Strong exception safety for free.
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// - Self assignment is handled implicitely.
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// - Simplicity.
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// - It just works and is hard to get wrong; i.e. you can use it without
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// even thinking about it to implement copy assignment whereever the
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// object data is managed indirectly via a pointer, which is very common.
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RefPtr<T_CppObject> temp (src);
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this->swap(temp);
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return *this;
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}
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template <class T_CppObject>
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template <class T_CastFrom>
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inline
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RefPtr<T_CppObject>& RefPtr<T_CppObject>::operator=(const RefPtr<T_CastFrom>& src)
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{
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RefPtr<T_CppObject> temp (src);
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this->swap(temp);
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return *this;
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}
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template <class T_CppObject> inline
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bool RefPtr<T_CppObject>::operator==(const RefPtr<T_CppObject>& src) const
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{
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return (pCppObject_ == src.pCppObject_);
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}
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template <class T_CppObject> inline
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bool RefPtr<T_CppObject>::operator!=(const RefPtr<T_CppObject>& src) const
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{
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return (pCppObject_ != src.pCppObject_);
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}
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template <class T_CppObject> inline
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RefPtr<T_CppObject>::operator bool() const
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{
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return (pCppObject_ != 0);
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}
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template <class T_CppObject> inline
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void RefPtr<T_CppObject>::clear()
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{
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RefPtr<T_CppObject> temp; // swap with an empty RefPtr<> to clear *this
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this->swap(temp);
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}
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template <class T_CppObject>
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template <class T_CastFrom>
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inline
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RefPtr<T_CppObject> RefPtr<T_CppObject>::cast_dynamic(const RefPtr<T_CastFrom>& src)
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{
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T_CppObject *const pCppObject = dynamic_cast<T_CppObject*>(src.operator->());
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if(pCppObject)
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pCppObject->reference();
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return RefPtr<T_CppObject>(pCppObject);
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}
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template <class T_CppObject>
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template <class T_CastFrom>
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inline
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RefPtr<T_CppObject> RefPtr<T_CppObject>::cast_static(const RefPtr<T_CastFrom>& src)
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{
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T_CppObject *const pCppObject = static_cast<T_CppObject*>(src.operator->());
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if(pCppObject)
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pCppObject->reference();
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return RefPtr<T_CppObject>(pCppObject);
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}
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template <class T_CppObject>
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template <class T_CastFrom>
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inline
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RefPtr<T_CppObject> RefPtr<T_CppObject>::cast_const(const RefPtr<T_CastFrom>& src)
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{
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T_CppObject *const pCppObject = const_cast<T_CppObject*>(src.operator->());
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if(pCppObject)
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pCppObject->reference();
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return RefPtr<T_CppObject>(pCppObject);
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}
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#endif /* DOXYGEN_SHOULD_SKIP_THIS */
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/** @relates Glib::RefPtr */
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template <class T_CppObject> inline
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void swap(RefPtr<T_CppObject>& lhs, RefPtr<T_CppObject>& rhs)
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{
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lhs.swap(rhs);
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}
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} // namespace Glib
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#endif /* _GLIBMM_REFPTR_H */
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