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Diffstat (limited to 'glib/glibmm/refptr.h')
-rw-r--r-- | glib/glibmm/refptr.h | 349 |
1 files changed, 349 insertions, 0 deletions
diff --git a/glib/glibmm/refptr.h b/glib/glibmm/refptr.h new file mode 100644 index 00000000..638a71b9 --- /dev/null +++ b/glib/glibmm/refptr.h @@ -0,0 +1,349 @@ +// -*- c++ -*- +#ifndef _GLIBMM_REFPTR_H +#define _GLIBMM_REFPTR_H + +/* $Id$ */ + +/* 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 is_null() will return true 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); + + // TODO: Get rid of this evilness. + /// For use only by the ::create() methods. + inline RefPtr<T_CppObject>& operator=(T_CppObject* pCppObject); + + /** 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; + + /// Test whether the RefPtr<> points to any underlying instance. + inline bool is_null() const; // whether there is no underlying instance + + + /// 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); + +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> inline +RefPtr<T_CppObject>& RefPtr<T_CppObject>::operator=(T_CppObject* pCppObject) +{ + RefPtr<T_CppObject> temp (pCppObject); + + // This extra reference is necessary because operator=(T_CppObject*) used + // to behave differently than the ctor RefPtr(T_CppObject*), i.e. it takes + // a reference. Unfortunately we can't fix it at this point. + // + // TODO: This assignment operator should be removed entirely at the next API break. + + if(pCppObject) + pCppObject->reference(); + + 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 +bool RefPtr<T_CppObject>::is_null() 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); +} + +#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 */ + |