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/* ScummVM - Graphic Adventure Engine
*
* ScummVM is the legal property of its developers, whose names
* are too numerous to list here. Please refer to the COPYRIGHT
* file distributed with this source distribution.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This program 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 General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* $URL$
* $Id$
*/
#ifndef COMMON_PTR_H
#define COMMON_PTR_H
#include "common/scummsys.h"
namespace Common {
/**
* A simple shared pointer implementation modelled after boost.
*
* This object keeps track of the assigned pointer and automatically
* frees it when no more SharedPtr references to it exist.
*
* To achieve that the object implements an internal reference counting.
* Thus you should try to avoid using the plain pointer after assigning
* it to a SharedPtr object for the first time. If you still use the
* plain pointer be sure you do not delete it on your own. You may also
* not use the plain pointer to create a new SharedPtr object, since that
* would result in a double deletion of the pointer sooner or later.
*
* Example creation:
* Common::SharedPtr<int> pointer(new int(1));
* would create a pointer to int. Later on usage via *pointer is the same
* as for a normal pointer. If you need to access the plain pointer value
* itself later on use the get method. The class also supplies a operator
* ->, which does the same as the -> operator on a normal pointer.
*
* Be sure you are using new to initialize the pointer you want to manage.
* Pointers pointing to memory not allocated by new, will cause undefined
* behavior on deletion. That is for example the case on pointers created
* with malloc (or similar) and new[]. This prevents the use of SharedPtr
* for arrays!
*
* Note that you have to specify the type itself not the pointer type as
* template parameter. You also need to have a real definition of the type
* you want to use, a simple forward definition is not enough.
*
* The class has implicit upcast support, so if you got a class B derived
* from class A, you can assign a pointer to B without any problems to a
* SharedPtr object with template parameter A. The very same applies to
* assigment of a SharedPtr<B> object to a SharedPtr<A> object.
*
* There are also operators != and == to compare two SharedPtr objects
* with compatible pointers.
*/
template<class T>
class SharedPtr {
template<class T2> friend class SharedPtr;
public:
typedef int RefValue;
typedef T ValueType;
typedef T *Pointer;
SharedPtr() : _refCount(0), _pointer(0) {}
template<class T2> explicit SharedPtr(T2 *p) : _refCount(new RefValue(1)), _pointer(p) {}
SharedPtr(const SharedPtr &r) : _refCount(r._refCount), _pointer(r._pointer) { if (_refCount) ++(*_refCount); }
template<class T2> SharedPtr(const SharedPtr<T2> &r) : _refCount(r._refCount), _pointer(r._pointer) { if (_refCount) ++(*_refCount); }
~SharedPtr() { decRef(); }
SharedPtr &operator =(const SharedPtr &r) {
if (r._refCount)
++(*r._refCount);
decRef();
_refCount = r._refCount;
_pointer = r._pointer;
return *this;
}
template<class T2>
SharedPtr &operator =(const SharedPtr<T2> &r) {
if (r._refCount)
++(*r._refCount);
decRef();
_refCount = r._refCount;
_pointer = r._pointer;
return *this;
}
ValueType &operator *() const { assert(_pointer); return *_pointer; }
Pointer operator ->() const { assert(_pointer); return _pointer; }
/**
* Returns the plain pointer value. Be sure you know what you
* do if you are continuing to use that pointer.
*
* @return the pointer the SharedPtr object manages
*/
Pointer get() const { return _pointer; }
operator bool() const { return _pointer != 0; }
/**
* Checks if the SharedPtr object is the only object refering
* to the assigned pointer. This should just be used for
* debugging purposes.
*/
bool unique() const { return refCount() == 1; }
/**
* Returns the number of references to the assigned pointer.
* This should just be used for debugging purposes.
*/
RefValue refCount() const { return _refCount ? *_refCount : 0; }
private:
void decRef() {
if (_refCount) {
--(*_refCount);
if (!*_refCount) {
delete _refCount;
delete _pointer;
_refCount = 0;
_pointer = 0;
}
}
}
RefValue *_refCount;
T *_pointer;
};
} // end of namespace Common
template<class T1, class T2>
bool operator ==(const Common::SharedPtr<T1> &l, const Common::SharedPtr<T2> &r) {
return l.get() == r.get();
}
template<class T1, class T2>
bool operator !=(const Common::SharedPtr<T1> &l, const Common::SharedPtr<T2> &r) {
return l.get() != r.get();
}
#endif
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