shared_ptr.h

/*          
 *             Copyright (C) 2005 Maarten Keijzer
 *
 *          This program is free software; you can redistribute it and/or modify
 *          it under the terms of version 2 of the GNU General Public License as 
 *          published by the Free Software Foundation. 
 *
 *          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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#ifndef _SHARED_PTR_H
#define _SHARED_PTR_H


template <class T> class weak_ptr;
    
template <class T>
class shared_ptr {
    private:
        T* ptr;
        unsigned* count; //

        /* special case, null pointer (nil-code) */
        static unsigned* nil() { static unsigned nil_counter(1); return &nil_counter; }
        
        void decref() { if (--(*count) == 0) { delete ptr; delete count; }} 
        void incref() { ++(*count); }
        
        friend class weak_ptr<T>;
        
    public:
        
        shared_ptr() : ptr(0), count(nil()) { incref(); }
        ~shared_ptr() { decref(); }
        
        shared_ptr(const shared_ptr<T>& o) : ptr(o.ptr), count(o.count) { incref(); }
        shared_ptr(T* p) : ptr(p), count(new unsigned(1)) {}
        explicit shared_ptr(const weak_ptr<T>& w) : ptr(w.ptr), count(w.count) { incref(); }
        
        shared_ptr<T>& operator=(const shared_ptr<T>& o) {
            if (ptr == o.ptr) return *this;
            decref();
            ptr = o.ptr;
            count = o.count;
            incref();
            return *this;
        }
        
        T* get() { return ptr; }
        T* operator->() { return ptr; }
        T& operator*()  { return *ptr; }

        const T* get() const { return ptr; }
        const T* operator->() const { return ptr; }
        const T& operator*() const { return *ptr; }

        bool operator==(const shared_ptr<T>& o) const { return ptr == o.ptr; }
        bool operator!=(const shared_ptr<T>& o) const { return ptr != o.ptr; }
        bool operator<(const shared_ptr<T>& o) const { return ptr < o.ptr; }    

        unsigned refcount() const { return *count; }
};

template <class T>
class weak_ptr {
        T* ptr;
        unsigned* count;
        
        friend class shared_ptr<T>;
        
    public:
        
        weak_ptr() : ptr(0), count(shared_ptr<T>::nil()) {}
        explicit weak_ptr( const shared_ptr<T>& s) : ptr(s.ptr), count(s.count) {}
        
        shared_ptr<T> lock() const { return shared_ptr<T>(*this); }

        
        T* get() { return ptr; }
        T* operator->() { return ptr; }
        T& operator*()  { return *ptr; }

        const T* get() const { return ptr; }
        const T* operator->() const { return ptr; }
        const T& operator*() const { return *ptr; }

        bool operator==(const shared_ptr<T>& o) const { return ptr == o.ptr; }
        bool operator!=(const shared_ptr<T>& o) const { return ptr != o.ptr; }
        bool operator<(const shared_ptr<T>& o) const { return ptr < o.ptr; }    
        
        unsigned refcount() const { return *count; }
        
};

#endif

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